difference between double dispatch and the method explains here
Hello, I just learned double dispatch. And now for the Robot challenge of exercism Tim has pointed me to this article(https://blog.metaobject.com/2019/04/accessors-have-message-obsession.html) but I fail to see how the move method looks like in that article. I had a conversation with Tim in the exercism channel and the way he explains it, it looks like double dispatch for me. Am I on the right track or do I oversee something here. Roelof
On 06/04/19 4:49 PM, Roelof Wobben wrote:
Hello,
I just learned double dispatch. And now for the Robot challenge of exercism Tim has pointed me to this article(https://blog.metaobject.com/2019/04/accessors-have-message-obsession.html)
but I fail to see how the move method looks like in that article. I had a conversation with Tim in the exercism channel and the way he explains it, it looks like double dispatch for me.
Am I on the right track or do I oversee something here. unary methods like moveRight perform specific ops and are not parametric, so only a single dispatch, depending on the receiver, is needed.
If you change it to move: aDistanceOrAngle, then performing requests like "move: 3 cms" or "move: 30 degrees" will depend not only on the receiver but also on the class of the argument. This would need double dispatch (aka multiple polymorphism). The first dispatch would be based on the receiver and the receiver's method would then dispatch it based on the class of the argument (i.e. Distance>>move or Angle>>move ) HTH .. Subbu
Op 6-4-2019 om 15:15 schreef K K Subbu:
On 06/04/19 4:49 PM, Roelof Wobben wrote:
Hello,
I just learned double dispatch. And now for the Robot challenge of exercism Tim has pointed me to this article(https://blog.metaobject.com/2019/04/accessors-have-message-obsession.html)
but I fail to see how the move method looks like in that article. I had a conversation with Tim in the exercism channel and the way he explains it, it looks like double dispatch for me.
Am I on the right track or do I oversee something here. unary methods like moveRight perform specific ops and are not parametric, so only a single dispatch, depending on the receiver, is needed.
If you change it to move: aDistanceOrAngle, then performing requests like "move: 3 cms" or "move: 30 degrees" will depend not only on the receiver but also on the class of the argument. This would need double dispatch (aka multiple polymorphism). The first dispatch would be based on the receiver and the receiver's method would then dispatch it based on the class of the argument (i.e. Distance>>move or Angle>>move )
HTH .. Subbu
hmm, still stuck I have now a class Direction with as instance variables north, south, east, west and made the accessors. then I thought I need a initialize like this : initialize   north = Direction( 0, -1).   east = Direction( 1, 0).   south = Direction( 0, 1).   west = Direction(-1, 0). but the Direction (0,-1) is a problem . the compiler does not like the (0,-1) part to give you the big picture. I have a Robot which can turnRight , turnLeft and moveForward and I try to understand how the page would work in my case. So I have a object Direction as described above and a Object MoveForward which is a subobject of Direction. MoveForward has only 1 method : IsMove   ^ 'A' Roelof
It would really REALLY **REALLY** help if we knew what the heck you were trying to do. There is an excellent chance that it is MUCH simpler than you think. If you cannot show us the Smalltalk version of the problem, can you show us the version for some other language? On Sun, 7 Apr 2019 at 20:15, Roelof Wobben <r.wobben@home.nl> wrote:
Op 6-4-2019 om 15:15 schreef K K Subbu:
On 06/04/19 4:49 PM, Roelof Wobben wrote:
Hello,
I just learned double dispatch. And now for the Robot challenge of exercism Tim has pointed me to this article( https://blog.metaobject.com/2019/04/accessors-have-message-obsession.html)
but I fail to see how the move method looks like in that article. I had a conversation with Tim in the exercism channel and the way he explains it, it looks like double dispatch for me.
Am I on the right track or do I oversee something here.
unary methods like moveRight perform specific ops and are not parametric, so only a single dispatch, depending on the receiver, is needed.
If you change it to move: aDistanceOrAngle, then performing requests like "move: 3 cms" or "move: 30 degrees" will depend not only on the receiver but also on the class of the argument. This would need double dispatch (aka multiple polymorphism). The first dispatch would be based on the receiver and the receiver's method would then dispatch it based on the class of the argument (i.e. Distance>>move or Angle>>move )
HTH .. Subbu
hmm, still stuck
I have now a class Direction with as instance variables north, south, east, west and made the accessors.
then I thought I need a initialize like this :
initialize north = Direction( 0, -1). east = Direction( 1, 0). south = Direction( 0, 1). west = Direction(-1, 0).
but the Direction (0,-1) is a problem . the compiler does not like the (0,-1) part
to give you the big picture. I have a Robot which can turnRight , turnLeft and moveForward and I try to understand how the page would work in my case.
So I have a object Direction as described above and a Object MoveForward which is a subobject of Direction. MoveForward has only 1 method :
IsMove ^ 'A'
Roelof
One thing I have often seen and lamented is students writing excessively complicated code with way too many classes. There is a huge difference between "A Robot knows its position and direction." and "A Robot has-a Position and has-a Direction." The first is the important one. The second is an over-commitment to too many classses. For a problem like this, you really really do not want a Direction class, and you certainly have no use for double dispatch. A position can be represented by a pair of integers x, y. It could also be represented by a Point with integer components. A direction could be represented by a pair of integers dx, dy such that |dx|+|dy| = 1. It could also be represented by a Point with integer components. For movement, you need to be able to add the direction to the location, which could be simply x := x + dx. y := y + dy. or it could be position := position + direction. For turning, you need to be able to rotate a direction vector by ninety degrees. Now it so happens that Point has methods #leftRotated and #rightRotated. So we can do the following: a Robot has position (a Point) and direction (aPoint) position := 0 @ 0. direction := 0 @ 1. To move forward without turning: position := position + direction. To turn left without moving: direction := direction leftRotated. To turn right without moving: direction := direction rightRotated. To obey a sequence of characters, commands: commands do: [:each | each caseOf: { [$A] -> [--move forward--]. [$L] -> [--turn left--]. [$R] -> [--turn right--] }]. One of the key ideas in extreme programming is "You Ain't Gonna Need It", abbreviated to YAGNI! The idea is *DON'T* generalise beyond your immediate needs. In this case, for example, the likelihood of *this* program needing to deal with more general kinds of movement is ZERO. And the only reason for using Point here instead of just using a few simple assignment statements is that Point already exists, so costs nothing to write, and as a familiar class, code using it should be easy to read. If someone challenges you to do something counter-productive, refuse the challenge. On Mon, 8 Apr 2019 at 17:21, Roelof Wobben <r.wobben@home.nl> wrote:
I can try to explain what I trying to solve.
I have a Robot which can turn left, turn right or moveForward.
now I have a string like 'LAR'
that means the robot needs to turn left (l) , move forward one place (A) and turn left. and I have to keep track to which direction the robot is facing and on which coordinate it stands.
so to summarize with the above string
lets say the robot is facing north on coordinate (0,0) then it has to turn left , so its facing east and still on coordinate (0,0) then it has to move forward, so its still facing east but are on coordinate(0,1) then it has to turn right, so its facing north and on coordinate (0,1)
and TimMacKinnon has challenged me to do this with double dispatch.
So I think now I need a object Direction, a sub object North and a sub - sub object TurnLeft, turnRight and moveForward.
So I can use double dispath first the direction North, East, South, West and then use double dispatch to find the right move.
Roelof
Op 8-4-2019 om 06:50 schreef Richard O'Keefe:
It would really REALLY **REALLY** help if we knew what the heck you were trying to do. There is an excellent chance that it is MUCH simpler than you think. If you cannot show us the Smalltalk version of the problem, can you show us the version for some other language?
On Sun, 7 Apr 2019 at 20:15, Roelof Wobben <r.wobben@home.nl> wrote:
Op 6-4-2019 om 15:15 schreef K K Subbu:
On 06/04/19 4:49 PM, Roelof Wobben wrote:
Hello,
I just learned double dispatch. And now for the Robot challenge of exercism Tim has pointed me to this article( https://blog.metaobject.com/2019/04/accessors-have-message-obsession.html)
but I fail to see how the move method looks like in that article. I had a conversation with Tim in the exercism channel and the way he explains it, it looks like double dispatch for me.
Am I on the right track or do I oversee something here.
unary methods like moveRight perform specific ops and are not parametric, so only a single dispatch, depending on the receiver, is needed.
If you change it to move: aDistanceOrAngle, then performing requests like "move: 3 cms" or "move: 30 degrees" will depend not only on the receiver but also on the class of the argument. This would need double dispatch (aka multiple polymorphism). The first dispatch would be based on the receiver and the receiver's method would then dispatch it based on the class of the argument (i.e. Distance>>move or Angle>>move )
HTH .. Subbu
hmm, still stuck
I have now a class Direction with as instance variables north, south, east, west and made the accessors.
then I thought I need a initialize like this :
initialize north = Direction( 0, -1). east = Direction( 1, 0). south = Direction( 0, 1). west = Direction(-1, 0).
but the Direction (0,-1) is a problem . the compiler does not like the (0,-1) part
to give you the big picture. I have a Robot which can turnRight , turnLeft and moveForward and I try to understand how the page would work in my case.
So I have a object Direction as described above and a Object MoveForward which is a subobject of Direction. MoveForward has only 1 method :
IsMove ^ 'A'
Roelof
The basic issue here is abstraction. An instance of "Robot" in your program is not a physical object. How could it possibly point North, South, or Nor-nor-west? It cannot. Its location and direction are abstract values *metaphorically* related to real world notions like position vectors and velocity vectors. "North" in this program is not a real thing, it is an *idea* which could be represented by 'North', 'north', #North, #north, $N, $n, 'Raki', 'raki', #Raki, #raki, $R, $r, 137, (0@ -1), a picture of the star Polaris, the colour red (the conventional colour for that end of a compass needle which points north), a sound recording of a lecture by Alfred North Whitehead, or anything you please, as long as, inside the program, it *acts* the way *you* want "north" to act (which is not necessarily the way the physical direction North acts, and in fact in this case it most certainly is not). Locations and movements in a 2D space are, in Smalltalk, commonly represented by Points. "Represented by." As for this method: test11_MovesTheRobotForward1SpaceInTheDirectionItIsPointingIncreasesTheYCoordinateOneWhenFacingNorth | result | result := robotSimulatorCalculator moveDirection: 'north' position: (Dictionary new add: 'x' -> 0; add: 'y' -> 0; yourself) instructions: 'A'. self assert: result equals: (Dictionary new add: 'direction' -> 'north'; add: 'position' -> (Dictionary new add: 'x' -> 0; add: 'y' -> 1; yourself); yourself) PLEASE tell me that is not what they are actually using. Let's start with (Dictionary new) add: k1 -> v1; ... add: kn -> vn; yourself Did you know that sending #add: to a dictionary is not portable? Storing actual Association objects inside Dictionaries was originally an encapsulation error and remains a performance error, so there are Smalltalks that do not make that mistake. The *portable* way to make a Dictionary is (Dictionary new) at: k1 put: v1; ... at: kn put: vn; yourself. And why in the name of sanity are the keys *strings* instead of *symbols*? This is not Smalltalk. It is Javascript in drag. Now exercism.io has a habit of insisting on particular implementations. For example, I completed the SML track, and found that the test code ONLY worked with Poly and not with any of the three SML implementations I already had on my machine. Since you are doing this in Pharo, I take it that exercism.io will insist on the Smalltalk track being done in Pharo, and in that case it is *nauseating* to use a Dictionary when you could use a Point. Old-fashioned Smalltalk style would have been to return something like #(<direction> <x> <y>) e.g. #(north 1 0), and I still prefer that. In fact *good* Smalltalk style for something like this would be test11_MovesTheRobotForward1SpaceInTheDirectionItIsPointingIncreasesTheYCoordinateOneWhenFacingNorth robotSimulatorCalculator moveTo: 0@0; head: #north; obey: 'A'. self assert: robotSimulatorCalculator heading equals: #north. self assert: robotSimulatorCalculator location equals: 0@1. -- We're starting to get the idea that identifiers like robotSimulatorCalculator are not a very good idea when simulatedRobot would do the job as well or better. (This is also pointing us towards Betrand Meyer's Command/Query Separation principle, but we shan't go there today.) This is important feedback to give to the exercism.io people. The test code should use a SMALLTALK interface, not a warmed-over JAVASCRIPT interface. Now, how do we map between direction *names* and direction *points*? Well, we have to start by laying down clearly what we *mean* by the directions. To move North one step is to add 1 to y and 0 to x. (We know that from the appalling test case above.) To move South one step is to add -1 to y and 0 to x. (South is the opposite of North.) To move East one step, oh we have a problem. THIS NEEDS SPELLING OUT. And one of the things the exercism.io exercises are HORRIBLY BAD AT is specifying the problem. Nearly every single exercise I have tried, I have been unable to tell what the problem is without examining the test cases, and that is not the way exercises are supposed to work. (Yeah, that's why I'm screaming about it. I've taught a class using exercises like this that were not of my writing and vague specifications really upset the students. People who had taken the class under someone else several years before were still angry about it.) The geometric classes in Smalltalk were written to support graphic user interfaces. And in user interfaces, the y coordinate increases DOWN. So if we take the compass rose and rotate it so that North is DOWN, it follows that West is right and East is left. So To move East one step is to add -1 to x and 0 to y. To move West one step is to add 1 to x and 0 to y. The chances are excellent that the problem specification is inconsistent with this. Sigh. Let's proceed, though. North 0@1 South 0@ -1 East -1@0 West 1@0 pointToName: aPoint ^aPoint x isZero ifTrue: [aPoint y > 0 ifTrue: [#north] ifFalse: [#south]] ifFalse: [aPoint x > 0 ifTrue: [#west ] ifFalse: [#east ]] nameToPoint: aSymbol aSymbol = #north ifTrue: [^0 @ 1]. aSymbol = #south ifTrue: [^0 @ -1]. aSymbol = #west ifTrue: [^1 @ 0]. aSymbol = #east ifTrue: [^-1 @ 0]. aSymbol error: 'not a compass direction in lower case'. Another problem I had with exercism was a "Space-Age" exercise where the README.md capitalised the planet names but test_Space-Age.<whatever> insisted on lower case. That might well happen here. Just for grins, Dictionary>> asPoint ^(self at: 'x') @ (self at: 'y') Point>> asDictionary ^(Dictionary new) at: 'x' put: self x; at: 'y' put: self y; yourself On Mon, 8 Apr 2019 at 22:15, Roelof Wobben <r.wobben@home.nl> wrote:
Richard thanks.
One thing I do not see direct.
you said :
A direction could be represented by a pair of integers dx, dy such that |dx|+|dy| = 1. It could also be represented by a Point with integer components.
for me a direction is the direction the robot is facing so something like north or east.
the challenge also wants a output like this :
test11_MovesTheRobotForward1SpaceInTheDirectionItIsPointingIncreasesTheYCoordinateOneWhenFacingNorth | result | result := robotSimulatorCalculator moveDirection: 'north' position: (Dictionary new add: 'x' -> 0; add: 'y' -> 0; yourself) instructions: 'A'. self assert: result equals: (Dictionary new add: 'direction' -> 'north'; add: 'position' -> (Dictionary new add: 'x' -> 0; add: 'y' -> 1; yourself); yourself)
so how do I "convert" the point you are using to the text.
Or do I misunderstood you somewhere wrong.
Roelof
Op 8-4-2019 om 10:57 schreef Richard O'Keefe:
One thing I have often seen and lamented is students writing excessively complicated code with way too many classes. There is a huge difference between "A Robot knows its position and direction." and "A Robot has-a Position and has-a Direction." The first is the important one. The second is an over-commitment to too many classses. For a problem like this, you really really do not want a Direction class, and you certainly have no use for double dispatch.
A position can be represented by a pair of integers x, y. It could also be represented by a Point with integer components.
A direction could be represented by a pair of integers dx, dy such that |dx|+|dy| = 1. It could also be represented by a Point with integer components.
For movement, you need to be able to add the direction to the location, which could be simply x := x + dx. y := y + dy. or it could be position := position + direction. For turning, you need to be able to rotate a direction vector by ninety degrees. Now it so happens that Point has methods #leftRotated and #rightRotated.
So we can do the following: a Robot has position (a Point) and direction (aPoint) position := 0 @ 0. direction := 0 @ 1. To move forward without turning: position := position + direction. To turn left without moving: direction := direction leftRotated. To turn right without moving: direction := direction rightRotated. To obey a sequence of characters, commands: commands do: [:each | each caseOf: { [$A] -> [--move forward--]. [$L] -> [--turn left--]. [$R] -> [--turn right--] }].
One of the key ideas in extreme programming is "You Ain't Gonna Need It", abbreviated to YAGNI! The idea is *DON'T* generalise beyond your immediate needs. In this case, for example, the likelihood of *this* program needing to deal with more general kinds of movement is ZERO. And the only reason for using Point here instead of just using a few simple assignment statements is that Point already exists, so costs nothing to write, and as a familiar class, code using it should be easy to read.
If someone challenges you to do something counter-productive, refuse the challenge.
On Mon, 8 Apr 2019 at 17:21, Roelof Wobben <r.wobben@home.nl> wrote:
I can try to explain what I trying to solve.
I have a Robot which can turn left, turn right or moveForward.
now I have a string like 'LAR'
that means the robot needs to turn left (l) , move forward one place (A) and turn left. and I have to keep track to which direction the robot is facing and on which coordinate it stands.
so to summarize with the above string
lets say the robot is facing north on coordinate (0,0) then it has to turn left , so its facing east and still on coordinate (0,0) then it has to move forward, so its still facing east but are on coordinate(0,1) then it has to turn right, so its facing north and on coordinate (0,1)
and TimMacKinnon has challenged me to do this with double dispatch.
So I think now I need a object Direction, a sub object North and a sub - sub object TurnLeft, turnRight and moveForward.
So I can use double dispath first the direction North, East, South, West and then use double dispatch to find the right move.
Roelof
Op 8-4-2019 om 06:50 schreef Richard O'Keefe:
It would really REALLY **REALLY** help if we knew what the heck you were trying to do. There is an excellent chance that it is MUCH simpler than you think. If you cannot show us the Smalltalk version of the problem, can you show us the version for some other language?
On Sun, 7 Apr 2019 at 20:15, Roelof Wobben <r.wobben@home.nl> wrote:
Op 6-4-2019 om 15:15 schreef K K Subbu:
On 06/04/19 4:49 PM, Roelof Wobben wrote:
Hello,
I just learned double dispatch. And now for the Robot challenge of exercism Tim has pointed me to this article( https://blog.metaobject.com/2019/04/accessors-have-message-obsession.html)
but I fail to see how the move method looks like in that article. I had a conversation with Tim in the exercism channel and the way he explains it, it looks like double dispatch for me.
Am I on the right track or do I oversee something here.
unary methods like moveRight perform specific ops and are not parametric, so only a single dispatch, depending on the receiver, is needed.
If you change it to move: aDistanceOrAngle, then performing requests like "move: 3 cms" or "move: 30 degrees" will depend not only on the receiver but also on the class of the argument. This would need double dispatch (aka multiple polymorphism). The first dispatch would be based on the receiver and the receiver's method would then dispatch it based on the class of the argument (i.e. Distance>>move or Angle>>move )
HTH .. Subbu
hmm, still stuck
I have now a class Direction with as instance variables north, south, east, west and made the accessors.
then I thought I need a initialize like this :
initialize north = Direction( 0, -1). east = Direction( 1, 0). south = Direction( 0, 1). west = Direction(-1, 0).
but the Direction (0,-1) is a problem . the compiler does not like the (0,-1) part
to give you the big picture. I have a Robot which can turnRight , turnLeft and moveForward and I try to understand how the page would work in my case.
So I have a object Direction as described above and a Object MoveForward which is a subobject of Direction. MoveForward has only 1 method :
IsMove ^ 'A'
Roelof
You are expected to use my code fragments for *ideas*, not to incorporate them *literally* in your code. As I explained, *without seeing the specification*, I have no way to tell whether the specification uses a left-handed or right-handed coordinate system. For what it's worth, here's a complete program in my Smalltalk dialect. It doesn't plug into the exercism testing framework because I can do not know what it looks like. But if it makes the code more complicated that this, it's doing it wrong. require: 'geometry.st' "Point" require: 'print.st' "OutputStream>>print:" Object subclass: #Robot instanceVariableNames: 'position direction' poolDirectionaries: 'FileStream' methods for: 'initialising' pvtPostNew position := 0@0. direction := 1@0. methods for: 'accessing' direction ^direction copy location ^location copy obey: commands commands do: [:each | each caseOf: { [$A] -> [position := position + direction]. [$L] -> [direction := direction leftRotated]. [$R] -> [direction := direction rightRotated] }]. class methods for: 'main' start [StdIn atEnd] whileFalse: [ |robot| robot := Robot new. Robot obey: StdIn nextLine. StdOut print: Robot location; cr]. On Tue, 9 Apr 2019 at 02:58, Roelof Wobben <r.wobben@home.nl> wrote:
yes, this is a real tests from the pharo track on exercism.io
I understand what you mean but maybe I overthinking things. But if we have a robot facing north and the robot turns to the left , im my oponion it faces now to the east.
like this test is saying :
test04_RotatesTheRobotsDirection90DegreesClockwiseChangesTheDirectionFromEastToSouth | result | result := robotSimulatorCalculator moveDirection: 'east' position: (Dictionary new add: 'x' -> 0; add: 'y' -> 0; yourself) instructions: 'R'. self assert: result equals: (Dictionary new add: 'direction' -> 'south'; add: 'position' -> (Dictionary new add: 'x' -> 0; add: 'y' -> 0; yourself); yourself)
but I cannot come to the same outcome with this code :
pointToName: aPoint ^aPoint x isZero ifTrue: [aPoint y > 0 ifTrue: [#north] ifFalse: [#south]] ifFalse: [aPoint x > 0 ifTrue: [#west ] ifFalse: [#east ]]
maybe exercism.io is not a good way to practice and learn smalltalk but I found not a better one. or smalltalk is not for me.
Roelof
Op 8-4-2019 om 16:44 schreef Richard O'Keefe:
The basic issue here is abstraction. An instance of "Robot" in your program is not a physical object. How could it possibly point North, South, or Nor-nor-west? It cannot. Its location and direction are abstract values *metaphorically* related to real world notions like position vectors and velocity vectors. "North" in this program is not a real thing, it is an *idea* which could be represented by 'North', 'north', #North, #north, $N, $n, 'Raki', 'raki', #Raki, #raki, $R, $r, 137, (0@ -1), a picture of the star Polaris, the colour red (the conventional colour for that end of a compass needle which points north), a sound recording of a lecture by Alfred North Whitehead, or anything you please, as long as, inside the program, it *acts* the way *you* want "north" to act (which is not necessarily the way the physical direction North acts, and in fact in this case it most certainly is not).
Locations and movements in a 2D space are, in Smalltalk, commonly represented by Points. "Represented by."
As for this method:
test11_MovesTheRobotForward1SpaceInTheDirectionItIsPointingIncreasesTheYCoordinateOneWhenFacingNorth | result | result := robotSimulatorCalculator moveDirection: 'north' position: (Dictionary new add: 'x' -> 0; add: 'y' -> 0; yourself) instructions: 'A'. self assert: result equals: (Dictionary new add: 'direction' -> 'north'; add: 'position' -> (Dictionary new add: 'x' -> 0; add: 'y' -> 1; yourself); yourself)
PLEASE tell me that is not what they are actually using. Let's start with (Dictionary new) add: k1 -> v1; ... add: kn -> vn; yourself Did you know that sending #add: to a dictionary is not portable? Storing actual Association objects inside Dictionaries was originally an encapsulation error and remains a performance error, so there are Smalltalks that do not make that mistake. The *portable* way to make a Dictionary is (Dictionary new) at: k1 put: v1; ... at: kn put: vn; yourself.
And why in the name of sanity are the keys *strings* instead of *symbols*? This is not Smalltalk. It is Javascript in drag.
Now exercism.io has a habit of insisting on particular implementations. For example, I completed the SML track, and found that the test code ONLY worked with Poly and not with any of the three SML implementations I already had on my machine. Since you are doing this in Pharo, I take it that exercism.io will insist on the Smalltalk track being done in Pharo, and in that case it is *nauseating* to use a Dictionary when you could use a Point. Old-fashioned Smalltalk style would have been to return something like #(<direction> <x> <y>) e.g. #(north 1 0), and I still prefer that.
In fact *good* Smalltalk style for something like this would be
test11_MovesTheRobotForward1SpaceInTheDirectionItIsPointingIncreasesTheYCoordinateOneWhenFacingNorth robotSimulatorCalculator moveTo: 0@0; head: #north; obey: 'A'. self assert: robotSimulatorCalculator heading equals: #north. self assert: robotSimulatorCalculator location equals: 0@1.
-- We're starting to get the idea that identifiers like robotSimulatorCalculator are not a very good idea when simulatedRobot would do the job as well or better.
(This is also pointing us towards Betrand Meyer's Command/Query Separation principle, but we shan't go there today.)
This is important feedback to give to the exercism.io people. The test code should use a SMALLTALK interface, not a warmed-over JAVASCRIPT interface.
Now, how do we map between direction *names* and direction *points*? Well, we have to start by laying down clearly what we *mean* by the directions.
To move North one step is to add 1 to y and 0 to x. (We know that from the appalling test case above.) To move South one step is to add -1 to y and 0 to x. (South is the opposite of North.) To move East one step, oh we have a problem. THIS NEEDS SPELLING OUT. And one of the things the exercism.io exercises are HORRIBLY BAD AT is specifying the problem. Nearly every single exercise I have tried, I have been unable to tell what the problem is without examining the test cases, and that is not the way exercises are supposed to work. (Yeah, that's why I'm screaming about it. I've taught a class using exercises like this that were not of my writing and vague specifications really upset the students. People who had taken the class under someone else several years before were still angry about it.)
The geometric classes in Smalltalk were written to support graphic user interfaces. And in user interfaces, the y coordinate increases DOWN. So if we take the compass rose and rotate it so that North is DOWN, it follows that West is right and East is left. So
To move East one step is to add -1 to x and 0 to y. To move West one step is to add 1 to x and 0 to y.
The chances are excellent that the problem specification is inconsistent with this. Sigh. Let's proceed, though.
North 0@1 South 0@ -1 East -1@0 West 1@0
pointToName: aPoint ^aPoint x isZero ifTrue: [aPoint y > 0 ifTrue: [#north] ifFalse: [#south]] ifFalse: [aPoint x > 0 ifTrue: [#west ] ifFalse: [#east ]]
nameToPoint: aSymbol aSymbol = #north ifTrue: [^0 @ 1]. aSymbol = #south ifTrue: [^0 @ -1]. aSymbol = #west ifTrue: [^1 @ 0]. aSymbol = #east ifTrue: [^-1 @ 0]. aSymbol error: 'not a compass direction in lower case'.
Another problem I had with exercism was a "Space-Age" exercise where the README.md capitalised the planet names but test_Space-Age.<whatever> insisted on lower case. That might well happen here.
Just for grins, Dictionary>> asPoint ^(self at: 'x') @ (self at: 'y')
Point>> asDictionary ^(Dictionary new) at: 'x' put: self x; at: 'y' put: self y; yourself
On Mon, 8 Apr 2019 at 22:15, Roelof Wobben <r.wobben@home.nl> wrote:
Richard thanks.
One thing I do not see direct.
you said :
A direction could be represented by a pair of integers dx, dy such that |dx|+|dy| = 1. It could also be represented by a Point with integer components.
for me a direction is the direction the robot is facing so something like north or east.
the challenge also wants a output like this :
test11_MovesTheRobotForward1SpaceInTheDirectionItIsPointingIncreasesTheYCoordinateOneWhenFacingNorth | result | result := robotSimulatorCalculator moveDirection: 'north' position: (Dictionary new add: 'x' -> 0; add: 'y' -> 0; yourself) instructions: 'A'. self assert: result equals: (Dictionary new add: 'direction' -> 'north'; add: 'position' -> (Dictionary new add: 'x' -> 0; add: 'y' -> 1; yourself); yourself)
so how do I "convert" the point you are using to the text.
Or do I misunderstood you somewhere wrong.
Roelof
Op 8-4-2019 om 10:57 schreef Richard O'Keefe:
One thing I have often seen and lamented is students writing excessively complicated code with way too many classes. There is a huge difference between "A Robot knows its position and direction." and "A Robot has-a Position and has-a Direction." The first is the important one. The second is an over-commitment to too many classses. For a problem like this, you really really do not want a Direction class, and you certainly have no use for double dispatch.
A position can be represented by a pair of integers x, y. It could also be represented by a Point with integer components.
A direction could be represented by a pair of integers dx, dy such that |dx|+|dy| = 1. It could also be represented by a Point with integer components.
For movement, you need to be able to add the direction to the location, which could be simply x := x + dx. y := y + dy. or it could be position := position + direction. For turning, you need to be able to rotate a direction vector by ninety degrees. Now it so happens that Point has methods #leftRotated and #rightRotated.
So we can do the following: a Robot has position (a Point) and direction (aPoint) position := 0 @ 0. direction := 0 @ 1. To move forward without turning: position := position + direction. To turn left without moving: direction := direction leftRotated. To turn right without moving: direction := direction rightRotated. To obey a sequence of characters, commands: commands do: [:each | each caseOf: { [$A] -> [--move forward--]. [$L] -> [--turn left--]. [$R] -> [--turn right--] }].
One of the key ideas in extreme programming is "You Ain't Gonna Need It", abbreviated to YAGNI! The idea is *DON'T* generalise beyond your immediate needs. In this case, for example, the likelihood of *this* program needing to deal with more general kinds of movement is ZERO. And the only reason for using Point here instead of just using a few simple assignment statements is that Point already exists, so costs nothing to write, and as a familiar class, code using it should be easy to read.
If someone challenges you to do something counter-productive, refuse the challenge.
On Mon, 8 Apr 2019 at 17:21, Roelof Wobben <r.wobben@home.nl> wrote:
I can try to explain what I trying to solve.
I have a Robot which can turn left, turn right or moveForward.
now I have a string like 'LAR'
that means the robot needs to turn left (l) , move forward one place (A) and turn left. and I have to keep track to which direction the robot is facing and on which coordinate it stands.
so to summarize with the above string
lets say the robot is facing north on coordinate (0,0) then it has to turn left , so its facing east and still on coordinate (0,0) then it has to move forward, so its still facing east but are on coordinate(0,1) then it has to turn right, so its facing north and on coordinate (0,1)
and TimMacKinnon has challenged me to do this with double dispatch.
So I think now I need a object Direction, a sub object North and a sub - sub object TurnLeft, turnRight and moveForward.
So I can use double dispath first the direction North, East, South, West and then use double dispatch to find the right move.
Roelof
Op 8-4-2019 om 06:50 schreef Richard O'Keefe:
It would really REALLY **REALLY** help if we knew what the heck you were trying to do. There is an excellent chance that it is MUCH simpler than you think. If you cannot show us the Smalltalk version of the problem, can you show us the version for some other language?
On Sun, 7 Apr 2019 at 20:15, Roelof Wobben <r.wobben@home.nl> wrote:
Op 6-4-2019 om 15:15 schreef K K Subbu:
On 06/04/19 4:49 PM, Roelof Wobben wrote:
Hello,
I just learned double dispatch. And now for the Robot challenge of exercism Tim has pointed me to this article( https://blog.metaobject.com/2019/04/accessors-have-message-obsession.html)
but I fail to see how the move method looks like in that article. I had a conversation with Tim in the exercism channel and the way he explains it, it looks like double dispatch for me.
Am I on the right track or do I oversee something here.
unary methods like moveRight perform specific ops and are not parametric, so only a single dispatch, depending on the receiver, is needed.
If you change it to move: aDistanceOrAngle, then performing requests like "move: 3 cms" or "move: 30 degrees" will depend not only on the receiver but also on the class of the argument. This would need double dispatch (aka multiple polymorphism). The first dispatch would be based on the receiver and the receiver's method would then dispatch it based on the class of the argument (i.e. Distance>>move or Angle>>move )
HTH .. Subbu
hmm, still stuck
I have now a class Direction with as instance variables north, south, east, west and made the accessors.
then I thought I need a initialize like this :
initialize north = Direction( 0, -1). east = Direction( 1, 0). south = Direction( 0, 1). west = Direction(-1, 0).
but the Direction (0,-1) is a problem . the compiler does not like the (0,-1) part
to give you the big picture. I have a Robot which can turnRight , turnLeft and moveForward and I try to understand how the page would work in my case.
So I have a object Direction as described above and a Object MoveForward which is a subobject of Direction. MoveForward has only 1 method :
IsMove ^ 'A'
Roelof
On this laptop I have - Squeak - Pharo - GNU Smalltalk - VisualAge Smalltalk - VisualWorks Smalltalk - Smalltalk/X plus some oddballs like susie, amber, and CSOM. On another laptop I have - Strongtalk - Dolphin And of course I have my own 'astc' Smalltalk-via-C compiler. I have to say that Dolphin is easily the most *beautiful* Smalltalk environment I've used. (Yes, I'm the kind of person who has four different C compilers on the same machine and uses them all. You don't want to know how many Javascript implementations...) The important thing here is that there are at least two aspects to "Smalltalk". There is Smalltalk-the-approach-to-OO and there is Smalltalk-the-many-related-but-different-IDEs. When it comes to productivity, the IDE is important. Really important. But when it comes to thinking about programming and solving tasks like exercism ones, it's the approach that matters. And that approach pays off in languages like Javascript and Ruby and Python as well. I used to be a University lecturer. Now I'm a (sub)contractor. I used to see a LOT of student code that - had way too many classes - did not use existing well-known classes when it should - failed to encapsulate private state - put responsibilities in the wrong places and that was Java code. What prepared me to see such issues in Java? Lots and lots of practice in Smalltalk. And lots of reading Smalltalk, and figuring out what made it easy or hard to read. I do not know how much time you have on your hands, but you might find it profitable to look at http://rosettacode.org/wiki/Rosetta_Code specifically http://rosettacode.org/wiki/Category:Smalltalk Look at the bottom of that page for a list of 258 problems solved in Smalltalk. On Tue, 9 Apr 2019 at 03:20, Roelof Wobben <r.wobben@home.nl> wrote:
Thanks,
for the discusson and lessons.
I will think about it and also think if smalltalk is for me. I did the pharo Mooc and still have a lot of problems making the smalltalk way click in my head so I can solve little problems like this.
Out of coriousy what dialect do you use?
Op 8-4-2019 om 17:11 schreef Richard O'Keefe:
You are expected to use my code fragments for *ideas*, not to incorporate them *literally* in your code. As I explained, *without seeing the specification*, I have no way to tell whether the specification uses a left-handed or right-handed coordinate system.
For what it's worth, here's a complete program in my Smalltalk dialect. It doesn't plug into the exercism testing framework because I can do not know what it looks like. But if it makes the code more complicated that this, it's doing it wrong.
require: 'geometry.st' "Point" require: 'print.st' "OutputStream>>print:"
Object subclass: #Robot instanceVariableNames: 'position direction' poolDirectionaries: 'FileStream'
methods for: 'initialising' pvtPostNew position := 0@0. direction := 1@0.
methods for: 'accessing' direction ^direction copy
location ^location copy
obey: commands commands do: [:each | each caseOf: { [$A] -> [position := position + direction]. [$L] -> [direction := direction leftRotated]. [$R] -> [direction := direction rightRotated] }].
class methods for: 'main' start [StdIn atEnd] whileFalse: [ |robot| robot := Robot new. Robot obey: StdIn nextLine. StdOut print: Robot location; cr].
On Tue, 9 Apr 2019 at 02:58, Roelof Wobben <r.wobben@home.nl> wrote:
yes, this is a real tests from the pharo track on exercism.io
I understand what you mean but maybe I overthinking things. But if we have a robot facing north and the robot turns to the left , im my oponion it faces now to the east.
like this test is saying :
test04_RotatesTheRobotsDirection90DegreesClockwiseChangesTheDirectionFromEastToSouth | result | result := robotSimulatorCalculator moveDirection: 'east' position: (Dictionary new add: 'x' -> 0; add: 'y' -> 0; yourself) instructions: 'R'. self assert: result equals: (Dictionary new add: 'direction' -> 'south'; add: 'position' -> (Dictionary new add: 'x' -> 0; add: 'y' -> 0; yourself); yourself)
but I cannot come to the same outcome with this code :
pointToName: aPoint ^aPoint x isZero ifTrue: [aPoint y > 0 ifTrue: [#north] ifFalse: [#south]] ifFalse: [aPoint x > 0 ifTrue: [#west ] ifFalse: [#east ]]
maybe exercism.io is not a good way to practice and learn smalltalk but I found not a better one. or smalltalk is not for me.
Roelof
Op 8-4-2019 om 16:44 schreef Richard O'Keefe:
The basic issue here is abstraction. An instance of "Robot" in your program is not a physical object. How could it possibly point North, South, or Nor-nor-west? It cannot. Its location and direction are abstract values *metaphorically* related to real world notions like position vectors and velocity vectors. "North" in this program is not a real thing, it is an *idea* which could be represented by 'North', 'north', #North, #north, $N, $n, 'Raki', 'raki', #Raki, #raki, $R, $r, 137, (0@ -1), a picture of the star Polaris, the colour red (the conventional colour for that end of a compass needle which points north), a sound recording of a lecture by Alfred North Whitehead, or anything you please, as long as, inside the program, it *acts* the way *you* want "north" to act (which is not necessarily the way the physical direction North acts, and in fact in this case it most certainly is not).
Locations and movements in a 2D space are, in Smalltalk, commonly represented by Points. "Represented by."
As for this method:
test11_MovesTheRobotForward1SpaceInTheDirectionItIsPointingIncreasesTheYCoordinateOneWhenFacingNorth | result | result := robotSimulatorCalculator moveDirection: 'north' position: (Dictionary new add: 'x' -> 0; add: 'y' -> 0; yourself) instructions: 'A'. self assert: result equals: (Dictionary new add: 'direction' -> 'north'; add: 'position' -> (Dictionary new add: 'x' -> 0; add: 'y' -> 1; yourself); yourself)
PLEASE tell me that is not what they are actually using. Let's start with (Dictionary new) add: k1 -> v1; ... add: kn -> vn; yourself Did you know that sending #add: to a dictionary is not portable? Storing actual Association objects inside Dictionaries was originally an encapsulation error and remains a performance error, so there are Smalltalks that do not make that mistake. The *portable* way to make a Dictionary is (Dictionary new) at: k1 put: v1; ... at: kn put: vn; yourself.
And why in the name of sanity are the keys *strings* instead of *symbols*? This is not Smalltalk. It is Javascript in drag.
Now exercism.io has a habit of insisting on particular implementations. For example, I completed the SML track, and found that the test code ONLY worked with Poly and not with any of the three SML implementations I already had on my machine. Since you are doing this in Pharo, I take it that exercism.io will insist on the Smalltalk track being done in Pharo, and in that case it is *nauseating* to use a Dictionary when you could use a Point. Old-fashioned Smalltalk style would have been to return something like #(<direction> <x> <y>) e.g. #(north 1 0), and I still prefer that.
In fact *good* Smalltalk style for something like this would be
test11_MovesTheRobotForward1SpaceInTheDirectionItIsPointingIncreasesTheYCoordinateOneWhenFacingNorth robotSimulatorCalculator moveTo: 0@0; head: #north; obey: 'A'. self assert: robotSimulatorCalculator heading equals: #north. self assert: robotSimulatorCalculator location equals: 0@1.
-- We're starting to get the idea that identifiers like robotSimulatorCalculator are not a very good idea when simulatedRobot would do the job as well or better.
(This is also pointing us towards Betrand Meyer's Command/Query Separation principle, but we shan't go there today.)
This is important feedback to give to the exercism.io people. The test code should use a SMALLTALK interface, not a warmed-over JAVASCRIPT interface.
Now, how do we map between direction *names* and direction *points*? Well, we have to start by laying down clearly what we *mean* by the directions.
To move North one step is to add 1 to y and 0 to x. (We know that from the appalling test case above.) To move South one step is to add -1 to y and 0 to x. (South is the opposite of North.) To move East one step, oh we have a problem. THIS NEEDS SPELLING OUT. And one of the things the exercism.io exercises are HORRIBLY BAD AT is specifying the problem. Nearly every single exercise I have tried, I have been unable to tell what the problem is without examining the test cases, and that is not the way exercises are supposed to work. (Yeah, that's why I'm screaming about it. I've taught a class using exercises like this that were not of my writing and vague specifications really upset the students. People who had taken the class under someone else several years before were still angry about it.)
The geometric classes in Smalltalk were written to support graphic user interfaces. And in user interfaces, the y coordinate increases DOWN. So if we take the compass rose and rotate it so that North is DOWN, it follows that West is right and East is left. So
To move East one step is to add -1 to x and 0 to y. To move West one step is to add 1 to x and 0 to y.
The chances are excellent that the problem specification is inconsistent with this. Sigh. Let's proceed, though.
North 0@1 South 0@ -1 East -1@0 West 1@0
pointToName: aPoint ^aPoint x isZero ifTrue: [aPoint y > 0 ifTrue: [#north] ifFalse: [#south]] ifFalse: [aPoint x > 0 ifTrue: [#west ] ifFalse: [#east ]]
nameToPoint: aSymbol aSymbol = #north ifTrue: [^0 @ 1]. aSymbol = #south ifTrue: [^0 @ -1]. aSymbol = #west ifTrue: [^1 @ 0]. aSymbol = #east ifTrue: [^-1 @ 0]. aSymbol error: 'not a compass direction in lower case'.
Another problem I had with exercism was a "Space-Age" exercise where the README.md capitalised the planet names but test_Space-Age.<whatever> insisted on lower case. That might well happen here.
Just for grins, Dictionary>> asPoint ^(self at: 'x') @ (self at: 'y')
Point>> asDictionary ^(Dictionary new) at: 'x' put: self x; at: 'y' put: self y; yourself
On Mon, 8 Apr 2019 at 22:15, Roelof Wobben <r.wobben@home.nl> wrote:
Richard thanks.
One thing I do not see direct.
you said :
A direction could be represented by a pair of integers dx, dy such that |dx|+|dy| = 1. It could also be represented by a Point with integer components.
for me a direction is the direction the robot is facing so something like north or east.
the challenge also wants a output like this :
test11_MovesTheRobotForward1SpaceInTheDirectionItIsPointingIncreasesTheYCoordinateOneWhenFacingNorth | result | result := robotSimulatorCalculator moveDirection: 'north' position: (Dictionary new add: 'x' -> 0; add: 'y' -> 0; yourself) instructions: 'A'. self assert: result equals: (Dictionary new add: 'direction' -> 'north'; add: 'position' -> (Dictionary new add: 'x' -> 0; add: 'y' -> 1; yourself); yourself)
so how do I "convert" the point you are using to the text.
Or do I misunderstood you somewhere wrong.
Roelof
Op 8-4-2019 om 10:57 schreef Richard O'Keefe:
One thing I have often seen and lamented is students writing excessively complicated code with way too many classes. There is a huge difference between "A Robot knows its position and direction." and "A Robot has-a Position and has-a Direction." The first is the important one. The second is an over-commitment to too many classses. For a problem like this, you really really do not want a Direction class, and you certainly have no use for double dispatch.
A position can be represented by a pair of integers x, y. It could also be represented by a Point with integer components.
A direction could be represented by a pair of integers dx, dy such that |dx|+|dy| = 1. It could also be represented by a Point with integer components.
For movement, you need to be able to add the direction to the location, which could be simply x := x + dx. y := y + dy. or it could be position := position + direction. For turning, you need to be able to rotate a direction vector by ninety degrees. Now it so happens that Point has methods #leftRotated and #rightRotated.
So we can do the following: a Robot has position (a Point) and direction (aPoint) position := 0 @ 0. direction := 0 @ 1. To move forward without turning: position := position + direction. To turn left without moving: direction := direction leftRotated. To turn right without moving: direction := direction rightRotated. To obey a sequence of characters, commands: commands do: [:each | each caseOf: { [$A] -> [--move forward--]. [$L] -> [--turn left--]. [$R] -> [--turn right--] }].
One of the key ideas in extreme programming is "You Ain't Gonna Need It", abbreviated to YAGNI! The idea is *DON'T* generalise beyond your immediate needs. In this case, for example, the likelihood of *this* program needing to deal with more general kinds of movement is ZERO. And the only reason for using Point here instead of just using a few simple assignment statements is that Point already exists, so costs nothing to write, and as a familiar class, code using it should be easy to read.
If someone challenges you to do something counter-productive, refuse the challenge.
On Mon, 8 Apr 2019 at 17:21, Roelof Wobben <r.wobben@home.nl> wrote:
I can try to explain what I trying to solve.
I have a Robot which can turn left, turn right or moveForward.
now I have a string like 'LAR'
that means the robot needs to turn left (l) , move forward one place (A) and turn left. and I have to keep track to which direction the robot is facing and on which coordinate it stands.
so to summarize with the above string
lets say the robot is facing north on coordinate (0,0) then it has to turn left , so its facing east and still on coordinate (0,0) then it has to move forward, so its still facing east but are on coordinate(0,1) then it has to turn right, so its facing north and on coordinate (0,1)
and TimMacKinnon has challenged me to do this with double dispatch.
So I think now I need a object Direction, a sub object North and a sub - sub object TurnLeft, turnRight and moveForward.
So I can use double dispath first the direction North, East, South, West and then use double dispatch to find the right move.
Roelof
Op 8-4-2019 om 06:50 schreef Richard O'Keefe:
It would really REALLY **REALLY** help if we knew what the heck you were trying to do. There is an excellent chance that it is MUCH simpler than you think. If you cannot show us the Smalltalk version of the problem, can you show us the version for some other language?
On Sun, 7 Apr 2019 at 20:15, Roelof Wobben <r.wobben@home.nl> wrote:
Op 6-4-2019 om 15:15 schreef K K Subbu:
On 06/04/19 4:49 PM, Roelof Wobben wrote:
Hello,
I just learned double dispatch. And now for the Robot challenge of exercism Tim has pointed me to this article( https://blog.metaobject.com/2019/04/accessors-have-message-obsession.html)
but I fail to see how the move method looks like in that article. I had a conversation with Tim in the exercism channel and the way
he
explains it, it looks like double dispatch for me.
Am I on the right track or do I oversee something here. unary methods like moveRight perform specific ops and are not parametric, so only a single dispatch, depending on the receiver, is needed.
If you change it to move: aDistanceOrAngle, then performing requests like "move: 3 cms" or "move: 30 degrees" will depend not only on the receiver but also on the class of the argument. This would need double dispatch (aka multiple polymorphism). The first dispatch would be based on the receiver and the receiver's method would then dispatch it based on the class of the argument (i.e. Distance>>move or Angle>>move )
HTH .. Subbu
hmm, still stuck
I have now a class Direction with as instance variables north, south, east, west and made the accessors.
then I thought I need a initialize like this :
initialize north = Direction( 0, -1). east = Direction( 1, 0). south = Direction( 0, 1). west = Direction(-1, 0).
but the Direction (0,-1) is a problem . the compiler does not like the (0,-1) part
to give you the big picture. I have a Robot which can turnRight , turnLeft and moveForward and I try to understand how the page would work in my case.
So I have a object Direction as described above and a Object MoveForward which is a subobject of Direction. MoveForward has only 1 method :
IsMove ^ 'A'
Roelof
Hi, Time to time I hear people like Richard saying âDolphin is the dialect most beautiful Smalltalk he usedâ and others praising it in different levels. As Pharo âarchitectâ (or whatever I am, but at least Iâm sure I have to pay attention to the IDE :P), Iâm interested to know what elements of Dolphin dialect you find âbeautifulâ, âenjoyableâ and productive. What it is? - the MVP? - integration with Windows? The way this integration is done? (If so⦠how is it done?) ⦠I am very interested on knowing this with some detail level. That doesnât mean I will react and do something, but I want to have a better understanding and put it in my radar to take inspiration to enhance the Pharo experience :P Esteban
On 10 Apr 2019, at 03:09, Richard O'Keefe <raoknz@gmail.com> wrote:
On this laptop I have - Squeak - Pharo - GNU Smalltalk - VisualAge Smalltalk - VisualWorks Smalltalk - Smalltalk/X plus some oddballs like susie, amber, and CSOM. On another laptop I have - Strongtalk - Dolphin And of course I have my own 'astc' Smalltalk-via-C compiler. I have to say that Dolphin is easily the most *beautiful* Smalltalk environment I've used. (Yes, I'm the kind of person who has four different C compilers on the same machine and uses them all. You don't want to know how many Javascript implementations...)
The important thing here is that there are at least two aspects to "Smalltalk". There is Smalltalk-the-approach-to-OO and there is Smalltalk-the-many-related-but-different-IDEs. When it comes to productivity, the IDE is important. Really important. But when it comes to thinking about programming and solving tasks like exercism ones, it's the approach that matters. And that approach pays off in languages like Javascript and Ruby and Python as well.
I used to be a University lecturer. Now I'm a (sub)contractor. I used to see a LOT of student code that - had way too many classes - did not use existing well-known classes when it should - failed to encapsulate private state - put responsibilities in the wrong places and that was Java code. What prepared me to see such issues in Java?
Lots and lots of practice in Smalltalk.
And lots of reading Smalltalk, and figuring out what made it easy or hard to read.
I do not know how much time you have on your hands, but you might find it profitable to look at http://rosettacode.org/wiki/Rosetta_Code <http://rosettacode.org/wiki/Rosetta_Code> specifically http://rosettacode.org/wiki/Category:Smalltalk <http://rosettacode.org/wiki/Category:Smalltalk>
Look at the bottom of that page for a list of 258 problems solved in Smalltalk.
On Tue, 9 Apr 2019 at 03:20, Roelof Wobben <r.wobben@home.nl <mailto:r.wobben@home.nl>> wrote: Thanks,
for the discusson and lessons.
I will think about it and also think if smalltalk is for me. I did the pharo Mooc and still have a lot of problems making the smalltalk way click in my head so I can solve little problems like this.
Out of coriousy what dialect do you use?
Op 8-4-2019 om 17:11 schreef Richard O'Keefe:
You are expected to use my code fragments for *ideas*, not to incorporate them *literally* in your code. As I explained, *without seeing the specification*, I have no way to tell whether the specification uses a left-handed or right-handed coordinate system.
For what it's worth, here's a complete program in my Smalltalk dialect. It doesn't plug into the exercism testing framework because I can do not know what it looks like. But if it makes the code more complicated that this, it's doing it wrong.
require: 'geometry.st <http://geometry.st/>' "Point" require: 'print.st <http://print.st/>' "OutputStream>>print:"
Object subclass: #Robot instanceVariableNames: 'position direction' poolDirectionaries: 'FileStream'
methods for: 'initialising' pvtPostNew position := 0@0. direction := 1@0.
methods for: 'accessing' direction ^direction copy
location ^location copy
obey: commands commands do: [:each | each caseOf: { [$A] -> [position := position + direction]. [$L] -> [direction := direction leftRotated]. [$R] -> [direction := direction rightRotated] }].
class methods for: 'main' start [StdIn atEnd] whileFalse: [ |robot| robot := Robot new. Robot obey: StdIn nextLine. StdOut print: Robot location; cr].
On Tue, 9 Apr 2019 at 02:58, Roelof Wobben <r.wobben@home.nl <mailto:r.wobben@home.nl>> wrote: yes, this is a real tests from the pharo track on exercism.io <http://exercism.io/>
I understand what you mean but maybe I overthinking things. But if we have a robot facing north and the robot turns to the left , im my oponion it faces now to the east.
like this test is saying :
test04_RotatesTheRobotsDirection90DegreesClockwiseChangesTheDirectionFromEastToSouth | result | result := robotSimulatorCalculator moveDirection: 'east' position: (Dictionary new add: 'x' -> 0; add: 'y' -> 0; yourself) instructions: 'R'. self assert: result equals: (Dictionary new add: 'direction' -> 'south'; add: 'position' -> (Dictionary new add: 'x' -> 0; add: 'y' -> 0; yourself); yourself)
but I cannot come to the same outcome with this code :
pointToName: aPoint ^aPoint x isZero ifTrue: [aPoint y > 0 ifTrue: [#north] ifFalse: [#south]] ifFalse: [aPoint x > 0 ifTrue: [#west ] ifFalse: [#east ]]
maybe exercism.io <http://exercism.io/> is not a good way to practice and learn smalltalk but I found not a better one. or smalltalk is not for me.
Roelof
Op 8-4-2019 om 16:44 schreef Richard O'Keefe:
The basic issue here is abstraction. An instance of "Robot" in your program is not a physical object. How could it possibly point North, South, or Nor-nor-west? It cannot. Its location and direction are abstract values *metaphorically* related to real world notions like position vectors and velocity vectors. "North" in this program is not a real thing, it is an *idea* which could be represented by 'North', 'north', #North, #north, $N, $n, 'Raki', 'raki', #Raki, #raki, $R, $r, 137, (0@ -1), a picture of the star Polaris, the colour red (the conventional colour for that end of a compass needle which points north), a sound recording of a lecture by Alfred North Whitehead, or anything you please, as long as, inside the program, it *acts* the way *you* want "north" to act (which is not necessarily the way the physical direction North acts, and in fact in this case it most certainly is not).
Locations and movements in a 2D space are, in Smalltalk, commonly represented by Points. "Represented by."
As for this method:
test11_MovesTheRobotForward1SpaceInTheDirectionItIsPointingIncreasesTheYCoordinateOneWhenFacingNorth | result | result := robotSimulatorCalculator moveDirection: 'north' position: (Dictionary new add: 'x' -> 0; add: 'y' -> 0; yourself) instructions: 'A'. self assert: result equals: (Dictionary new add: 'direction' -> 'north'; add: 'position' -> (Dictionary new add: 'x' -> 0; add: 'y' -> 1; yourself); yourself)
PLEASE tell me that is not what they are actually using. Let's start with (Dictionary new) add: k1 -> v1; ... add: kn -> vn; yourself Did you know that sending #add: to a dictionary is not portable? Storing actual Association objects inside Dictionaries was originally an encapsulation error and remains a performance error, so there are Smalltalks that do not make that mistake. The *portable* way to make a Dictionary is (Dictionary new) at: k1 put: v1; ... at: kn put: vn; yourself.
And why in the name of sanity are the keys *strings* instead of *symbols*? This is not Smalltalk. It is Javascript in drag.
Now exercism.io <http://exercism.io/> has a habit of insisting on particular implementations. For example, I completed the SML track, and found that the test code ONLY worked with Poly and not with any of the three SML implementations I already had on my machine. Since you are doing this in Pharo, I take it that exercism.io <http://exercism.io/> will insist on the Smalltalk track being done in Pharo, and in that case it is *nauseating* to use a Dictionary when you could use a Point. Old-fashioned Smalltalk style would have been to return something like #(<direction> <x> <y>) e.g. #(north 1 0), and I still prefer that.
In fact *good* Smalltalk style for something like this would be test11_MovesTheRobotForward1SpaceInTheDirectionItIsPointingIncreasesTheYCoordinateOneWhenFacingNorth robotSimulatorCalculator moveTo: 0@0; head: #north; obey: 'A'. self assert: robotSimulatorCalculator heading equals: #north. self assert: robotSimulatorCalculator location equals: 0@1.
-- We're starting to get the idea that identifiers like robotSimulatorCalculator are not a very good idea when simulatedRobot would do the job as well or better.
(This is also pointing us towards Betrand Meyer's Command/Query Separation principle, but we shan't go there today.)
This is important feedback to give to the exercism.io <http://exercism.io/> people. The test code should use a SMALLTALK interface, not a warmed-over JAVASCRIPT interface.
Now, how do we map between direction *names* and direction *points*? Well, we have to start by laying down clearly what we *mean* by the directions.
To move North one step is to add 1 to y and 0 to x. (We know that from the appalling test case above.) To move South one step is to add -1 to y and 0 to x. (South is the opposite of North.) To move East one step, oh we have a problem. THIS NEEDS SPELLING OUT. And one of the things the exercism.io <http://exercism.io/> exercises are HORRIBLY BAD AT is specifying the problem. Nearly every single exercise I have tried, I have been unable to tell what the problem is without examining the test cases, and that is not the way exercises are supposed to work. (Yeah, that's why I'm screaming about it. I've taught a class using exercises like this that were not of my writing and vague specifications really upset the students. People who had taken the class under someone else several years before were still angry about it.)
The geometric classes in Smalltalk were written to support graphic user interfaces. And in user interfaces, the y coordinate increases DOWN. So if we take the compass rose and rotate it so that North is DOWN, it follows that West is right and East is left. So
To move East one step is to add -1 to x and 0 to y. To move West one step is to add 1 to x and 0 to y.
The chances are excellent that the problem specification is inconsistent with this. Sigh. Let's proceed, though.
North 0@1 South 0@ -1 East -1@0 West 1@0
pointToName: aPoint ^aPoint x isZero ifTrue: [aPoint y > 0 ifTrue: [#north] ifFalse: [#south]] ifFalse: [aPoint x > 0 ifTrue: [#west ] ifFalse: [#east ]]
nameToPoint: aSymbol aSymbol = #north ifTrue: [^0 @ 1]. aSymbol = #south ifTrue: [^0 @ -1]. aSymbol = #west ifTrue: [^1 @ 0]. aSymbol = #east ifTrue: [^-1 @ 0]. aSymbol error: 'not a compass direction in lower case'.
Another problem I had with exercism was a "Space-Age" exercise where the README.md capitalised the planet names but test_Space-Age.<whatever> insisted on lower case. That might well happen here.
Just for grins, Dictionary>> asPoint ^(self at: 'x') @ (self at: 'y')
Point>> asDictionary ^(Dictionary new) at: 'x' put: self x; at: 'y' put: self y; yourself
On Mon, 8 Apr 2019 at 22:15, Roelof Wobben <r.wobben@home.nl <mailto:r.wobben@home.nl>> wrote: Richard thanks.
One thing I do not see direct.
you said :
A direction could be represented by a pair of integers dx, dy such that |dx|+|dy| = 1. It could also be represented by a Point with integer components.
for me a direction is the direction the robot is facing so something like north or east.
the challenge also wants a output like this :
test11_MovesTheRobotForward1SpaceInTheDirectionItIsPointingIncreasesTheYCoordinateOneWhenFacingNorth | result | result := robotSimulatorCalculator moveDirection: 'north' position: (Dictionary new add: 'x' -> 0; add: 'y' -> 0; yourself) instructions: 'A'. self assert: result equals: (Dictionary new add: 'direction' -> 'north'; add: 'position' -> (Dictionary new add: 'x' -> 0; add: 'y' -> 1; yourself); yourself)
so how do I "convert" the point you are using to the text.
Or do I misunderstood you somewhere wrong.
Roelof
Op 8-4-2019 om 10:57 schreef Richard O'Keefe:
One thing I have often seen and lamented is students writing excessively complicated code with way too many classes. There is a huge difference between "A Robot knows its position and direction." and "A Robot has-a Position and has-a Direction." The first is the important one. The second is an over-commitment to too many classses. For a problem like this, you really really do not want a Direction class, and you certainly have no use for double dispatch.
A position can be represented by a pair of integers x, y. It could also be represented by a Point with integer components.
A direction could be represented by a pair of integers dx, dy such that |dx|+|dy| = 1. It could also be represented by a Point with integer components.
For movement, you need to be able to add the direction to the location, which could be simply x := x + dx. y := y + dy. or it could be position := position + direction. For turning, you need to be able to rotate a direction vector by ninety degrees. Now it so happens that Point has methods #leftRotated and #rightRotated.
So we can do the following: a Robot has position (a Point) and direction (aPoint) position := 0 @ 0. direction := 0 @ 1. To move forward without turning: position := position + direction. To turn left without moving: direction := direction leftRotated. To turn right without moving: direction := direction rightRotated. To obey a sequence of characters, commands: commands do: [:each | each caseOf: { [$A] -> [--move forward--]. [$L] -> [--turn left--]. [$R] -> [--turn right--] }].
One of the key ideas in extreme programming is "You Ain't Gonna Need It", abbreviated to YAGNI! The idea is *DON'T* generalise beyond your immediate needs. In this case, for example, the likelihood of *this* program needing to deal with more general kinds of movement is ZERO. And the only reason for using Point here instead of just using a few simple assignment statements is that Point already exists, so costs nothing to write, and as a familiar class, code using it should be easy to read.
If someone challenges you to do something counter-productive, refuse the challenge.
On Mon, 8 Apr 2019 at 17:21, Roelof Wobben <r.wobben@home.nl <mailto:r.wobben@home.nl>> wrote: I can try to explain what I trying to solve.
I have a Robot which can turn left, turn right or moveForward.
now I have a string like 'LAR'
that means the robot needs to turn left (l) , move forward one place (A) and turn left. and I have to keep track to which direction the robot is facing and on which coordinate it stands.
so to summarize with the above string
lets say the robot is facing north on coordinate (0,0) then it has to turn left , so its facing east and still on coordinate (0,0) then it has to move forward, so its still facing east but are on coordinate(0,1) then it has to turn right, so its facing north and on coordinate (0,1)
and TimMacKinnon has challenged me to do this with double dispatch.
So I think now I need a object Direction, a sub object North and a sub - sub object TurnLeft, turnRight and moveForward.
So I can use double dispath first the direction North, East, South, West and then use double dispatch to find the right move.
Roelof
Op 8-4-2019 om 06:50 schreef Richard O'Keefe:
It would really REALLY **REALLY** help if we knew what the heck you were trying to do. There is an excellent chance that it is MUCH simpler than you think. If you cannot show us the Smalltalk version of the problem, can you show us the version for some other language?
On Sun, 7 Apr 2019 at 20:15, Roelof Wobben <r.wobben@home.nl <mailto:r.wobben@home.nl>> wrote: Op 6-4-2019 om 15:15 schreef K K Subbu:
On 06/04/19 4:49 PM, Roelof Wobben wrote:
Hello,
I just learned double dispatch. And now for the Robot challenge of exercism Tim has pointed me to this article(https://blog.metaobject.com/2019/04/accessors-have-message-obsession.html <https://blog.metaobject.com/2019/04/accessors-have-message-obsession.html>)
but I fail to see how the move method looks like in that article. I had a conversation with Tim in the exercism channel and the way he explains it, it looks like double dispatch for me.
Am I on the right track or do I oversee something here. unary methods like moveRight perform specific ops and are not parametric, so only a single dispatch, depending on the receiver, is needed.
If you change it to move: aDistanceOrAngle, then performing requests like "move: 3 cms" or "move: 30 degrees" will depend not only on the receiver but also on the class of the argument. This would need double dispatch (aka multiple polymorphism). The first dispatch would be based on the receiver and the receiver's method would then dispatch it based on the class of the argument (i.e. Distance>>move or Angle>>move )
HTH .. Subbu
hmm, still stuck
I have now a class Direction with as instance variables north, south, east, west and made the accessors.
then I thought I need a initialize like this :
initialize north = Direction( 0, -1). east = Direction( 1, 0). south = Direction( 0, 1). west = Direction(-1, 0).
but the Direction (0,-1) is a problem . the compiler does not like the (0,-1) part
to give you the big picture. I have a Robot which can turnRight , turnLeft and moveForward and I try to understand how the page would work in my case.
So I have a object Direction as described above and a Object MoveForward which is a subobject of Direction. MoveForward has only 1 method :
IsMove ^ 'A'
Roelof
Esteban, I can, of course, only speak for myself and I must admit I never really used Dolphin for more extensive projects. What I always was envious of as a long-time VA Smalltalk-user was the nice look & feel of Dolphin. It just felt like Windows, acted and looked like Windows and offered all those neat little "newer" widgets (at the time) that IBM simply ignored and let their users dry off from. The very same reason once made me excited about Ambrai Smalltalk, which was nicely integrated with MacOS X at the day. Like Dolphin, which more or less capitulated from the .net transition, Ambrai died because it was based on Carbon and coult not easily be adapted to Cocoa. I'd like to not start a flame war, but one thing that (I think) turns people away from most Smalltalks is that they neither look nor feel like a native application on any of the platforms they support. The only one that does is probably ObjectStudio. The web seemed to change the game, but then we fell behind all those frontend technologies that run in the Browser. Smalltalk is not very present/prominent in that field (yet?). The first impression of Pharo and almost all other Smalltalks is probably that if that thing looks so "different" and maybe even "old fashioned", how can that possibly be a modern, highly productive development environment? I personally like the Approach of WindowBuilder and/or SWT for building GUIs, but MVP also works very well and had a few nice side effects when it comes to exchanging teh presentation of a ViewModel. So MVP is probably also a sweet spot of Dolphin. I once was a big fan of IBM's Composition editor, but these days I'd go for WindowBuilder rather than CompEditor. I like the ability to change both code and visual representation, whatever fits my needs. Just my 2 cents Joachim Am 10.04.19 um 08:25 schrieb Esteban Lorenzano:
Hi,
Time to time I hear people like Richard saying âDolphin is the dialect most beautiful Smalltalk he usedâ and others praising it in different levels. As Pharo âarchitectâ (or whatever I am, but at least Iâm sure I have to pay attention to the IDE :P), Iâm interested to know what elements of Dolphin dialect you find âbeautifulâ, âenjoyableâ and productive. What it is?
- the MVP? - integration with Windows? The way this integration is done? (If so⦠how is it done?) â¦
I am very interested on knowing this with some detail level. That doesnât mean I will react and do something, but I want to have a better understanding and put it in my radar to take inspiration to enhance the Pharo experience :P
Esteban
On 10 Apr 2019, at 03:09, Richard O'Keefe <raoknz@gmail.com <mailto:raoknz@gmail.com>> wrote:
On this laptop I have  - Squeak  - Pharo  - GNU Smalltalk  - VisualAge Smalltalk  - VisualWorks Smalltalk  - Smalltalk/X plus some oddballs like susie, amber, and CSOM. On another laptop I have  - Strongtalk  - Dolphin And of course I have my own 'astc' Smalltalk-via-C compiler. I have to say that Dolphin is easily the most *beautiful* Smalltalk environment I've used. (Yes, I'm the kind of person who has four different C compilers on the same machine and uses them all. You don't want to know how many Javascript implementations...)
The important thing here is that there are at least two aspects to "Smalltalk". There is Smalltalk-the-approach-to-OO and there is Smalltalk-the-many-related-but-different-IDEs. When it comes to productivity, the IDE is important. Really important. But when it comes to thinking about programming and solving tasks like exercism ones, it's the approach that matters. And that approach pays off in languages like Javascript and Ruby and Python as well.
I used to be a University lecturer. Now I'm a (sub)contractor. I used to see a LOT of student code that  - had way too many classes  - did not use existing well-known classes when it should  - failed to encapsulate private state  - put responsibilities in the wrong places and that was Java code. What prepared me to see such issues in Java?
Lots and lots of practice in Smalltalk.
And lots of reading Smalltalk, and figuring out what made it easy or hard to read.
I do not know how much time you have on your hands, but you might find it profitable to look at http://rosettacode.org/wiki/Rosetta_Code specifically http://rosettacode.org/wiki/Category:Smalltalk
Look at the bottom of that page for a list of 258 problems solved in Smalltalk.
On Tue, 9 Apr 2019 at 03:20, Roelof Wobben <r.wobben@home.nl <mailto:r.wobben@home.nl>> wrote:
Thanks,
for the discusson and lessons.
I will think about it and also think if smalltalk is for me. I did the pharo Mooc and still have a lot of problems making the smalltalk way click in my head so I can solve little problems like this.
Out of coriousy what dialect do you use?
Op 8-4-2019 om 17:11 schreef Richard O'Keefe:
You are expected to use my code fragments for *ideas*, not to incorporate them *literally* in your code. As I explained, *without seeing the specification*, I have no way to tell whether the specification uses a left-handed or right-handed coordinate system.
For what it's worth, here's a complete program in my Smalltalk dialect. It doesn't plug into the exercism testing framework because I can do not know what it looks like. But if it makes the code more complicated that this, it's doing it wrong.
require: 'geometry.st <http://geometry.st/>' "Point" require: 'print.st <http://print.st/>' "OutputStream>>print:"
Object subclass: #Robot  instanceVariableNames: 'position direction'  poolDirectionaries:   'FileStream'
 methods for: 'initialising'    pvtPostNew      position := 0@0.      direction := 1@0.
 methods for: 'accessing'    direction      ^direction copy
   location      ^location copy
   obey: commands      commands do: [:each |        each caseOf: {          [$A] -> [position := position + direction].          [$L] -> [direction := direction leftRotated].          [$R] -> [direction := direction rightRotated]        }].
 class methods for: 'main'    start      [StdIn atEnd] whileFalse: [         |robot|         robot := Robot new.         Robot obey: StdIn nextLine.         StdOut print: Robot location; cr].
On Tue, 9 Apr 2019 at 02:58, Roelof Wobben <r.wobben@home.nl <mailto:r.wobben@home.nl>> wrote:
yes, this is a real tests from the pharo track on exercism.io <http://exercism.io/>
I understand what you mean but maybe I overthinking things. But if we have a robot facing north and the robot turns to the left , im my oponion it faces now to the east.
like this test is saying :
test04_RotatesTheRobotsDirection90DegreesClockwiseChangesTheDirectionFromEastToSouth    | result |    result := robotSimulatorCalculator       moveDirection: 'east'       position:          (Dictionary new             add: 'x' -> 0;             add: 'y' -> 0;             yourself)       instructions: 'R'.    self       assert: result       equals:          (Dictionary new             add: 'direction' -> 'south';             add:                'position'                   ->                      (Dictionary new                         add: 'x' -> 0;                         add: 'y' -> 0;                         yourself);             yourself)
but I cannot come to the same outcome with this code :
pointToName: aPoint ^aPoint x isZero ifTrue:Â [aPoint y > 0 ifTrue: [#north] ifFalse: [#south]] ifFalse: [aPoint x > 0 ifTrue: [#west ] ifFalse: [#east ]]
maybe exercism.io <http://exercism.io/> is not a good way to practice and learn smalltalk but I found not a better one. or smalltalk is not for me.
Roelof
Op 8-4-2019 om 16:44 schreef Richard O'Keefe:
The basic issue here is abstraction. An instance of "Robot" in your program is not a physical object. How could it possibly point North, South, or Nor-nor-west? It cannot. Its location and direction are abstract values *metaphorically* related to real world notions like position vectors and velocity vectors. "North" in this program is not a real thing, it is an *idea* which could be represented by 'North', 'north', #North, #north, $N, $n, 'Raki', 'raki', #Raki, #raki, $R, $r, 137, (0@ -1), a picture of the star Polaris, the colour red (the conventional colour for that end of a compass needle which points north), a sound recording of a lecture by Alfred North Whitehead, or anything you please, as long as, inside the program, it *acts* the way *you* want "north" to act (which is not necessarily the way the physical direction North acts, and in fact in this case it most certainly is not).
Locations and movements in a 2D space are, in Smalltalk, commonly represented by Points. "Represented by."
As for this method:
test11_MovesTheRobotForward1SpaceInTheDirectionItIsPointingIncreasesTheYCoordinateOneWhenFacingNorth    | result |    result := robotSimulatorCalculator       moveDirection: 'north'       position:          (Dictionary new             add: 'x' -> 0;             add: 'y' -> 0;             yourself)       instructions: 'A'.    self       assert: result       equals:          (Dictionary new             add: 'direction' -> 'north';             add:                'position'                   -> (Dictionary new                         add: 'x' -> 0;                         add: 'y' -> 1; yourself);             yourself)
PLEASE tell me that is not what they are actually using. Let's start with (Dictionary new) add: k1 -> v1; ... add: kn -> vn; yourself Did you know that sending #add: to a dictionary is not portable? Storing actual Association objects inside Dictionaries was originally an encapsulation error and remains a performance error, so there are Smalltalks that do not make that mistake. The *portable* way to make a Dictionary is (Dictionary new) at: k1 put: v1; ... at: kn put: vn; yourself.
And why in the name of sanity are the keys *strings* instead of *symbols*? This is not Smalltalk. It is Javascript in drag.
Now exercism.io <http://exercism.io/> has a habit of insisting on particular implementations. For example, I completed the SML track, and found that the test code ONLY worked with Poly and not with any of the three SML implementations I already had on my machine. Since you are doing this in Pharo, I take it that exercism.io <http://exercism.io/> will insist on the Smalltalk track being done in Pharo, and in that case it is *nauseating* to use a Dictionary when you could use a Point. Old-fashioned Smalltalk style would have been to return something like #(<direction> <x> <y>) e.g. #(north 1 0), and I still prefer that.
In fact *good* Smalltalk style for something like this would be test11_MovesTheRobotForward1SpaceInTheDirectionItIsPointingIncreasesTheYCoordinateOneWhenFacingNorth  robotSimulatorCalculator moveTo: 0@0; head: #north; obey: 'A'. self assert: robotSimulatorCalculator heading equals: #north. self assert: robotSimulatorCalculator location equals: 0@1.
-- We're starting to get the idea that identifiers like robotSimulatorCalculator are not a very good idea when simulatedRobot would do the job as well or better.
(This is also pointing us towards Betrand Meyer's Command/Query Separation principle, but we shan't go there today.)
This is important feedback to give to the exercism.io <http://exercism.io/> people. The test code should use a SMALLTALK interface, not a warmed-over JAVASCRIPT interface.
Now, how do we map between direction *names* and direction *points*? Well, we have to start by laying down clearly what we *mean* by the directions.
To move North one step is to add 1 to y and 0 to x. (We know that from the appalling test case above.) To move South one step is to add -1 to y and 0 to x. (South is the opposite of North.) To move East one step, oh we have a problem. THIS NEEDS SPELLING OUT. And one of the things the exercism.io <http://exercism.io/> exercises are HORRIBLY BAD AT is specifying the problem. Nearly every single exercise I have tried, I have been unable to tell what the problem is without examining the test cases, and that is not the way exercises are supposed to work. (Yeah, that's why I'm screaming about it. I've taught a class using exercises like this that were not of my writing and vague specifications really upset the students. People who had taken the class under someone else several years before were still angry about it.)
The geometric classes in Smalltalk were written to support graphic user interfaces. And in user interfaces, the y coordinate increases DOWN. So if we take the compass rose and rotate it so that North is DOWN, it follows that West is right and East is left. So
To move East one step is to add -1 to x and 0 to y. To move West one step is to add 1 to x and 0 to y.
The chances are excellent that the problem specification is inconsistent with this. Sigh. Let's proceed, though.
North 0@1 South 0@ -1 East -1@0 West 1@0
pointToName: aPoint ^aPoint x isZero ifTrue:Â [aPoint y > 0 ifTrue: [#north] ifFalse: [#south]] ifFalse: [aPoint x > 0 ifTrue: [#west ] ifFalse: [#east ]]
nameToPoint: aSymbol aSymbol = #north ifTrue: [^0 @ 1]. aSymbol = #south ifTrue: [^0 @ -1]. aSymbol = #west ifTrue: [^1 @ 0]. aSymbol = #east ifTrue: [^-1 @ 0]. aSymbol error: 'not a compass direction in lower case'.
Another problem I had with exercism was a "Space-Age" exercise where the README.md capitalised the planet names but test_Space-Age.<whatever> insisted on lower case. That might well happen here.
Just for grins, Dictionary>> asPoint ^(self at: 'x') @ (self at: 'y')
Point>> asDictionary ^(Dictionary new) at: 'x' put: self x; at: 'y' put: self y; yourself
On Mon, 8 Apr 2019 at 22:15, Roelof Wobben <r.wobben@home.nl <mailto:r.wobben@home.nl>> wrote:
Richard thanks.
One thing I do not see direct.
you said :
A direction could be represented by a pair of integers dx, dy such that |dx|+|dy| = 1. It could also be represented by a Point with integer components.
for me a direction is the direction the robot is facing so something like north or east.
the challenge also wants a output like this :
test11_MovesTheRobotForward1SpaceInTheDirectionItIsPointingIncreasesTheYCoordinateOneWhenFacingNorth    | result |    result := robotSimulatorCalculator       moveDirection: 'north'       position:          (Dictionary new             add: 'x' -> 0;             add: 'y' -> 0;             yourself)       instructions: 'A'.    self       assert: result       equals:          (Dictionary new             add: 'direction' -> 'north';             add:                'position'                   -> (Dictionary new add: 'x' -> 0; add: 'y' -> 1; yourself);             yourself)
so how do I "convert" the point you are using to the text.
Or do I misunderstood you somewhere wrong.
Roelof
Op 8-4-2019 om 10:57 schreef Richard O'Keefe:
One thing I have often seen and lamented is students writing excessively complicated code with way too many classes. There is a huge difference between "A Robot knows its position and direction." and "A Robot has-a Position and has-a Direction." The first is the important one. The second is an over-commitment to too many classses. For a problem like this, you really really do not want a Direction class, and you certainly have no use for double dispatch.
A position can be represented by a pair of integers x, y. It could also be represented by a Point with integer components.
A direction could be represented by a pair of integers dx, dy such that |dx|+|dy| = 1. It could also be represented by a Point with integer components.
For movement, you need to be able to add the direction to the location, which could be simply x := x + dx. y := y + dy. or it could be position := position + direction. For turning, you need to be able to rotate a direction vector by ninety degrees. Now it so happens that Point has methods #leftRotated and #rightRotated.
So we can do the following: a Robot has position (a Point) and direction (aPoint) position := 0 @ 0. direction := 0 @ 1. To move forward without turning: position := position + direction. To turn left without moving: direction := direction leftRotated. To turn right without moving: direction := direction rightRotated. To obey a sequence of characters, commands: commands do: [:each | each caseOf: { [$A] -> [--move forward--]. [$L] -> [--turn left--]. [$R] -> [--turn right--] }].
One of the key ideas in extreme programming is "You Ain't Gonna Need It", abbreviated to YAGNI! The idea is *DON'T* generalise beyond your immediate needs. In this case, for example, the likelihood of *this* program needing to deal with more general kinds of movement is ZERO. And the only reason for using Point here instead of just using a few simple assignment statements is that Point already exists, so costs nothing to write, and as a familiar class, code using it should be easy to read.
If someone challenges you to do something counter-productive, refuse the challenge.
On Mon, 8 Apr 2019 at 17:21, Roelof Wobben <r.wobben@home.nl <mailto:r.wobben@home.nl>> wrote:
I can try to explain what I trying to solve.
I have a Robot which can turn left, turn right or moveForward.
now I have a string like 'LAR'
that means the robot needs to turn left (l) , move forward one place (A) and turn left. and I have to keep track to which direction the robot is facing and on which coordinate it stands.
so to summarize with the above string
lets say the robot is facing north on coordinate (0,0) then it has to turn left , so its facing east and still on coordinate (0,0) then it has to move forward, so its still facing east but are on coordinate(0,1) then it has to turn right, so its facing north and on coordinate (0,1)
and TimMacKinnon has challenged me to do this with double dispatch.
So I think now I need a object Direction, a sub object North and a sub - sub object TurnLeft, turnRight and moveForward.
So I can use double dispath first the direction North, East, South, West and then use double dispatch to find the right move.
Roelof
Op 8-4-2019 om 06:50 schreef Richard O'Keefe:
It would really REALLY **REALLY** help if we knew what the heck you were trying to do. There is an excellent chance that it is MUCH simpler than you think. If you cannot show us the Smalltalk version of the problem, can you show us the version for some other language?
On Sun, 7 Apr 2019 at 20:15, Roelof Wobben <r.wobben@home.nl <mailto:r.wobben@home.nl>> wrote:
Op 6-4-2019 om 15:15 schreef K K Subbu: > On 06/04/19 4:49 PM, Roelof Wobben wrote: >> Hello, >> >> I just learned double dispatch. >> And now for the Robot challenge of exercism Tim has pointed me to >> this >> article(https://blog.metaobject.com/2019/04/accessors-have-message-obsession.html)
>> >> but I fail to see how the move method looks like in that article. >> I had a conversation with Tim in the exercism channel and the way he >> explains it, it looks like double dispatch for me. >> >> Am I on the right track or do I oversee something here. > unary methods like moveRight perform specific ops and are not > parametric, so only a single dispatch, depending on the receiver, is > needed. > > If you change it to move: aDistanceOrAngle, then performing requests > like "move: 3 cms" or "move: 30 degrees" will depend not only on the > receiver but also on the class of the argument. This would need double > dispatch (aka multiple polymorphism). The first dispatch would be > based on the receiver and the receiver's method would then dispatch it > based on the class of the argument (i.e. Distance>>move or Angle>>move ) > > HTH .. Subbu > >
hmm, still stuck
I have now a class Direction with as instance variables north, south, east, west and made the accessors.
then I thought I need a initialize like this :
initialize    north = Direction( 0, -1).    east = Direction( 1, 0).    south = Direction( 0, 1).    west = Direction(-1, 0).
but the Direction (0,-1)Â is a problem . the compiler does not like the (0,-1) part
to give you the big picture. I have a Robot which can turnRight , turnLeft and moveForward and I try to understand how the page would work in my case.
So I have a object Direction as described above and a Object MoveForward which is a subobject of Direction. MoveForward has only 1 method :
IsMove    ^ 'A'
Roelof
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There are three questions there: "beautiful", "enjoyable", and "productive". On the subject of beauty, I would classify this way: (0) Ugly. VisualAge. Now the VisualAge people have over the years put a *huge* amount of work into making VAST a serious contender for commercial programming. But aesthetics of the basic IDE, no. I would say that the original Smalltalk-80 was more attractive. Dark grey text on medium grey background is not the most readable. I have attached a screenshot of a browser window. (1) VisualWorks. This has come a long way, and it isn't bad. If you look at the screenshot for that, you'll see that the text is fuzzy, and part of "beauty" for me is effortlessly readable text. (2) GNU Smalltalk gst-browser goes to the opposite extreme from VAST and VW. They go for lots of separate cramped little windows. GST takes over your whole screen for one browser window. What makes GST poor is that at least under Ubuntu 18.04 it spews a huge number of error messages on the terminal you start it from. (3) Squeak and Pharo. At the level of aesthetics, I find Squeak 5 and Pharo 7 about the same. They pass the "effortlessly readable" test. Pharo has an edge in the individual tools; Squeak feels more "playful", if that makes sense. (4) Dolphin has simply had a lot of work put into two things: Windows integration, and aesthetics. It just *looks* gorgeous. It looks as though it has been designed by a professional graphic designer, yet nobody who has read the coloured books or Inside Smalltalk should have any trouble with the IDE. There is one place where it falls down, and that is that no attention seems to have been given to the spelling of comments, hint hint. Enjoyability. (0) Not only is reading a pain in VAST, but on Linux I find that the shortcut keys do not work. This is surprisingly unpleasant. The browser is not a five pane browser. The methods are divided into layers by package. A method may appear in more than one layer. (1) VW isn't too bad, but there are some glitches. For example, Browse|Implementors of selector| scroll through an alphabetic list and guess| whoops, the list has gone! Yes, there's a list of implementors, but I guessed wrong, I need to start again from the beginning. One thing that rather irritated me some years ago was wanting to use some ANSI methods, finding that they were not there, implementing them myself, and then discovering that there was an ANSI compatibility package that was not loaded by default. Now here is an idea. If I type a shell command in linux, and mistype it, it tells me which packages define a command by that name. E.g., % mb foo.st foo.ost Command 'mb' not found, but can be installed with: sudo apt install mrbayes Wouldn't it be nice if using an undefined class or selector meant you were offered a list of "well known" packages that define it? (2) I haven't used the GNU Smalltalk GUI enough to comment. (3) My main issue with Pharo is that I never know from one release to the next what a facility will be called or where it will be in the menu hierarchy. I also detest editors that by default *force* their style on me, and I find that displaying a selector as you type it just gets in my way, often obscuring something I need to see. However, after spending about an hour to customise more settings than I ever want to know about, it's a pleasure to use. (How are beginners supposed to guess that 'Iceberg' has something to do with version control?) (4) Dolphin's browser has a minor issue or two which I have forgotten, but mostly it's a joy to use. The main thing is that so *much* effort has gone into the GUI and into Windows integration that there's rather less in other things. Productivity. Here so much depends on what you are doing and whether there is a package available for it that I will say no more. On Wed, 10 Apr 2019 at 18:26, Esteban Lorenzano <estebanlm@gmail.com> wrote:
Hi,
Time to time I hear people like Richard saying âDolphin is the dialect most beautiful Smalltalk he usedâ and others praising it in different levels. As Pharo âarchitectâ (or whatever I am, but at least Iâm sure I have to pay attention to the IDE :P), Iâm interested to know what elements of Dolphin dialect you find âbeautifulâ, âenjoyableâ and productive. What it is?
- the MVP? - integration with Windows? The way this integration is done? (If so⦠how is it done?) â¦
I am very interested on knowing this with some detail level. That doesnât mean I will react and do something, but I want to have a better understanding and put it in my radar to take inspiration to enhance the Pharo experience :P
Esteban
On 10 Apr 2019, at 03:09, Richard O'Keefe <raoknz@gmail.com> wrote:
On this laptop I have - Squeak - Pharo - GNU Smalltalk - VisualAge Smalltalk - VisualWorks Smalltalk - Smalltalk/X plus some oddballs like susie, amber, and CSOM. On another laptop I have - Strongtalk - Dolphin And of course I have my own 'astc' Smalltalk-via-C compiler. I have to say that Dolphin is easily the most *beautiful* Smalltalk environment I've used. (Yes, I'm the kind of person who has four different C compilers on the same machine and uses them all. You don't want to know how many Javascript implementations...)
The important thing here is that there are at least two aspects to "Smalltalk". There is Smalltalk-the-approach-to-OO and there is Smalltalk-the-many-related-but-different-IDEs. When it comes to productivity, the IDE is important. Really important. But when it comes to thinking about programming and solving tasks like exercism ones, it's the approach that matters. And that approach pays off in languages like Javascript and Ruby and Python as well.
I used to be a University lecturer. Now I'm a (sub)contractor. I used to see a LOT of student code that - had way too many classes - did not use existing well-known classes when it should - failed to encapsulate private state - put responsibilities in the wrong places and that was Java code. What prepared me to see such issues in Java?
Lots and lots of practice in Smalltalk.
And lots of reading Smalltalk, and figuring out what made it easy or hard to read.
I do not know how much time you have on your hands, but you might find it profitable to look at http://rosettacode.org/wiki/Rosetta_Code specifically http://rosettacode.org/wiki/Category:Smalltalk
Look at the bottom of that page for a list of 258 problems solved in Smalltalk.
On Tue, 9 Apr 2019 at 03:20, Roelof Wobben <r.wobben@home.nl> wrote:
Thanks,
for the discusson and lessons.
I will think about it and also think if smalltalk is for me. I did the pharo Mooc and still have a lot of problems making the smalltalk way click in my head so I can solve little problems like this.
Out of coriousy what dialect do you use?
Op 8-4-2019 om 17:11 schreef Richard O'Keefe:
You are expected to use my code fragments for *ideas*, not to incorporate them *literally* in your code. As I explained, *without seeing the specification*, I have no way to tell whether the specification uses a left-handed or right-handed coordinate system.
For what it's worth, here's a complete program in my Smalltalk dialect. It doesn't plug into the exercism testing framework because I can do not know what it looks like. But if it makes the code more complicated that this, it's doing it wrong.
require: 'geometry.st' "Point" require: 'print.st' "OutputStream>>print:"
Object subclass: #Robot instanceVariableNames: 'position direction' poolDirectionaries: 'FileStream'
methods for: 'initialising' pvtPostNew position := 0@0. direction := 1@0.
methods for: 'accessing' direction ^direction copy
location ^location copy
obey: commands commands do: [:each | each caseOf: { [$A] -> [position := position + direction]. [$L] -> [direction := direction leftRotated]. [$R] -> [direction := direction rightRotated] }].
class methods for: 'main' start [StdIn atEnd] whileFalse: [ |robot| robot := Robot new. Robot obey: StdIn nextLine. StdOut print: Robot location; cr].
On Tue, 9 Apr 2019 at 02:58, Roelof Wobben <r.wobben@home.nl> wrote:
yes, this is a real tests from the pharo track on exercism.io
I understand what you mean but maybe I overthinking things. But if we have a robot facing north and the robot turns to the left , im my oponion it faces now to the east.
like this test is saying :
test04_RotatesTheRobotsDirection90DegreesClockwiseChangesTheDirectionFromEastToSouth | result | result := robotSimulatorCalculator moveDirection: 'east' position: (Dictionary new add: 'x' -> 0; add: 'y' -> 0; yourself) instructions: 'R'. self assert: result equals: (Dictionary new add: 'direction' -> 'south'; add: 'position' -> (Dictionary new add: 'x' -> 0; add: 'y' -> 0; yourself); yourself)
but I cannot come to the same outcome with this code :
pointToName: aPoint ^aPoint x isZero ifTrue: [aPoint y > 0 ifTrue: [#north] ifFalse: [#south]] ifFalse: [aPoint x > 0 ifTrue: [#west ] ifFalse: [#east ]]
maybe exercism.io is not a good way to practice and learn smalltalk but I found not a better one. or smalltalk is not for me.
Roelof
Op 8-4-2019 om 16:44 schreef Richard O'Keefe:
The basic issue here is abstraction. An instance of "Robot" in your program is not a physical object. How could it possibly point North, South, or Nor-nor-west? It cannot. Its location and direction are abstract values *metaphorically* related to real world notions like position vectors and velocity vectors. "North" in this program is not a real thing, it is an *idea* which could be represented by 'North', 'north', #North, #north, $N, $n, 'Raki', 'raki', #Raki, #raki, $R, $r, 137, (0@ -1), a picture of the star Polaris, the colour red (the conventional colour for that end of a compass needle which points north), a sound recording of a lecture by Alfred North Whitehead, or anything you please, as long as, inside the program, it *acts* the way *you* want "north" to act (which is not necessarily the way the physical direction North acts, and in fact in this case it most certainly is not).
Locations and movements in a 2D space are, in Smalltalk, commonly represented by Points. "Represented by."
As for this method:
test11_MovesTheRobotForward1SpaceInTheDirectionItIsPointingIncreasesTheYCoordinateOneWhenFacingNorth | result | result := robotSimulatorCalculator moveDirection: 'north' position: (Dictionary new add: 'x' -> 0; add: 'y' -> 0; yourself) instructions: 'A'. self assert: result equals: (Dictionary new add: 'direction' -> 'north'; add: 'position' -> (Dictionary new add: 'x' -> 0; add: 'y' -> 1; yourself); yourself)
PLEASE tell me that is not what they are actually using. Let's start with (Dictionary new) add: k1 -> v1; ... add: kn -> vn; yourself Did you know that sending #add: to a dictionary is not portable? Storing actual Association objects inside Dictionaries was originally an encapsulation error and remains a performance error, so there are Smalltalks that do not make that mistake. The *portable* way to make a Dictionary is (Dictionary new) at: k1 put: v1; ... at: kn put: vn; yourself.
And why in the name of sanity are the keys *strings* instead of *symbols*? This is not Smalltalk. It is Javascript in drag.
Now exercism.io has a habit of insisting on particular implementations. For example, I completed the SML track, and found that the test code ONLY worked with Poly and not with any of the three SML implementations I already had on my machine. Since you are doing this in Pharo, I take it that exercism.io will insist on the Smalltalk track being done in Pharo, and in that case it is *nauseating* to use a Dictionary when you could use a Point. Old-fashioned Smalltalk style would have been to return something like #(<direction> <x> <y>) e.g. #(north 1 0), and I still prefer that.
In fact *good* Smalltalk style for something like this would be
test11_MovesTheRobotForward1SpaceInTheDirectionItIsPointingIncreasesTheYCoordinateOneWhenFacingNorth robotSimulatorCalculator moveTo: 0@0; head: #north; obey: 'A'. self assert: robotSimulatorCalculator heading equals: #north. self assert: robotSimulatorCalculator location equals: 0@1.
-- We're starting to get the idea that identifiers like robotSimulatorCalculator are not a very good idea when simulatedRobot would do the job as well or better.
(This is also pointing us towards Betrand Meyer's Command/Query Separation principle, but we shan't go there today.)
This is important feedback to give to the exercism.io people. The test code should use a SMALLTALK interface, not a warmed-over JAVASCRIPT interface.
Now, how do we map between direction *names* and direction *points*? Well, we have to start by laying down clearly what we *mean* by the directions.
To move North one step is to add 1 to y and 0 to x. (We know that from the appalling test case above.) To move South one step is to add -1 to y and 0 to x. (South is the opposite of North.) To move East one step, oh we have a problem. THIS NEEDS SPELLING OUT. And one of the things the exercism.io exercises are HORRIBLY BAD AT is specifying the problem. Nearly every single exercise I have tried, I have been unable to tell what the problem is without examining the test cases, and that is not the way exercises are supposed to work. (Yeah, that's why I'm screaming about it. I've taught a class using exercises like this that were not of my writing and vague specifications really upset the students. People who had taken the class under someone else several years before were still angry about it.)
The geometric classes in Smalltalk were written to support graphic user interfaces. And in user interfaces, the y coordinate increases DOWN. So if we take the compass rose and rotate it so that North is DOWN, it follows that West is right and East is left. So
To move East one step is to add -1 to x and 0 to y. To move West one step is to add 1 to x and 0 to y.
The chances are excellent that the problem specification is inconsistent with this. Sigh. Let's proceed, though.
North 0@1 South 0@ -1 East -1@0 West 1@0
pointToName: aPoint ^aPoint x isZero ifTrue: [aPoint y > 0 ifTrue: [#north] ifFalse: [#south]] ifFalse: [aPoint x > 0 ifTrue: [#west ] ifFalse: [#east ]]
nameToPoint: aSymbol aSymbol = #north ifTrue: [^0 @ 1]. aSymbol = #south ifTrue: [^0 @ -1]. aSymbol = #west ifTrue: [^1 @ 0]. aSymbol = #east ifTrue: [^-1 @ 0]. aSymbol error: 'not a compass direction in lower case'.
Another problem I had with exercism was a "Space-Age" exercise where the README.md capitalised the planet names but test_Space-Age.<whatever> insisted on lower case. That might well happen here.
Just for grins, Dictionary>> asPoint ^(self at: 'x') @ (self at: 'y')
Point>> asDictionary ^(Dictionary new) at: 'x' put: self x; at: 'y' put: self y; yourself
On Mon, 8 Apr 2019 at 22:15, Roelof Wobben <r.wobben@home.nl> wrote:
Richard thanks.
One thing I do not see direct.
you said :
A direction could be represented by a pair of integers dx, dy such that |dx|+|dy| = 1. It could also be represented by a Point with integer components.
for me a direction is the direction the robot is facing so something like north or east.
the challenge also wants a output like this :
test11_MovesTheRobotForward1SpaceInTheDirectionItIsPointingIncreasesTheYCoordinateOneWhenFacingNorth | result | result := robotSimulatorCalculator moveDirection: 'north' position: (Dictionary new add: 'x' -> 0; add: 'y' -> 0; yourself) instructions: 'A'. self assert: result equals: (Dictionary new add: 'direction' -> 'north'; add: 'position' -> (Dictionary new add: 'x' -> 0; add: 'y' -> 1; yourself); yourself)
so how do I "convert" the point you are using to the text.
Or do I misunderstood you somewhere wrong.
Roelof
Op 8-4-2019 om 10:57 schreef Richard O'Keefe:
One thing I have often seen and lamented is students writing excessively complicated code with way too many classes. There is a huge difference between "A Robot knows its position and direction." and "A Robot has-a Position and has-a Direction." The first is the important one. The second is an over-commitment to too many classses. For a problem like this, you really really do not want a Direction class, and you certainly have no use for double dispatch.
A position can be represented by a pair of integers x, y. It could also be represented by a Point with integer components.
A direction could be represented by a pair of integers dx, dy such that |dx|+|dy| = 1. It could also be represented by a Point with integer components.
For movement, you need to be able to add the direction to the location, which could be simply x := x + dx. y := y + dy. or it could be position := position + direction. For turning, you need to be able to rotate a direction vector by ninety degrees. Now it so happens that Point has methods #leftRotated and #rightRotated.
So we can do the following: a Robot has position (a Point) and direction (aPoint) position := 0 @ 0. direction := 0 @ 1. To move forward without turning: position := position + direction. To turn left without moving: direction := direction leftRotated. To turn right without moving: direction := direction rightRotated. To obey a sequence of characters, commands: commands do: [:each | each caseOf: { [$A] -> [--move forward--]. [$L] -> [--turn left--]. [$R] -> [--turn right--] }].
One of the key ideas in extreme programming is "You Ain't Gonna Need It", abbreviated to YAGNI! The idea is *DON'T* generalise beyond your immediate needs. In this case, for example, the likelihood of *this* program needing to deal with more general kinds of movement is ZERO. And the only reason for using Point here instead of just using a few simple assignment statements is that Point already exists, so costs nothing to write, and as a familiar class, code using it should be easy to read.
If someone challenges you to do something counter-productive, refuse the challenge.
On Mon, 8 Apr 2019 at 17:21, Roelof Wobben <r.wobben@home.nl> wrote:
I can try to explain what I trying to solve.
I have a Robot which can turn left, turn right or moveForward.
now I have a string like 'LAR'
that means the robot needs to turn left (l) , move forward one place (A) and turn left. and I have to keep track to which direction the robot is facing and on which coordinate it stands.
so to summarize with the above string
lets say the robot is facing north on coordinate (0,0) then it has to turn left , so its facing east and still on coordinate (0,0) then it has to move forward, so its still facing east but are on coordinate(0,1) then it has to turn right, so its facing north and on coordinate (0,1)
and TimMacKinnon has challenged me to do this with double dispatch.
So I think now I need a object Direction, a sub object North and a sub - sub object TurnLeft, turnRight and moveForward.
So I can use double dispath first the direction North, East, South, West and then use double dispatch to find the right move.
Roelof
Op 8-4-2019 om 06:50 schreef Richard O'Keefe:
It would really REALLY **REALLY** help if we knew what the heck you were trying to do. There is an excellent chance that it is MUCH simpler than you think. If you cannot show us the Smalltalk version of the problem, can you show us the version for some other language?
On Sun, 7 Apr 2019 at 20:15, Roelof Wobben <r.wobben@home.nl> wrote:
Op 6-4-2019 om 15:15 schreef K K Subbu:
On 06/04/19 4:49 PM, Roelof Wobben wrote:
Hello,
I just learned double dispatch. And now for the Robot challenge of exercism Tim has pointed me to this article( https://blog.metaobject.com/2019/04/accessors-have-message-obsession.html)
but I fail to see how the move method looks like in that article. I had a conversation with Tim in the exercism channel and the way
he
explains it, it looks like double dispatch for me.
Am I on the right track or do I oversee something here. unary methods like moveRight perform specific ops and are not parametric, so only a single dispatch, depending on the receiver, is needed.
If you change it to move: aDistanceOrAngle, then performing requests like "move: 3 cms" or "move: 30 degrees" will depend not only on the receiver but also on the class of the argument. This would need double dispatch (aka multiple polymorphism). The first dispatch would be based on the receiver and the receiver's method would then dispatch it based on the class of the argument (i.e. Distance>>move or Angle>>move )
HTH .. Subbu
hmm, still stuck
I have now a class Direction with as instance variables north, south, east, west and made the accessors.
then I thought I need a initialize like this :
initialize north = Direction( 0, -1). east = Direction( 1, 0). south = Direction( 0, 1). west = Direction(-1, 0).
but the Direction (0,-1) is a problem . the compiler does not like the (0,-1) part
to give you the big picture. I have a Robot which can turnRight , turnLeft and moveForward and I try to understand how the page would work in my case.
So I have a object Direction as described above and a Object MoveForward which is a subobject of Direction. MoveForward has only 1 method :
IsMove ^ 'A'
Roelof
Richard, as a comment on VA Smalltalk: you are referring to the Linux version, which is also your Screenshot. I agree that Linux version of VA Smalltalk is far from what I'd call enjoyable or beautiful. If you take a look at the Windows version of VAST, you'll immediately realize that Linux users miss a lot of nice stuff that has been added to VA Smalltalk over the last few releases. The reason here is most likely that commercial Smalltalk projects mainly target Windows. This has changed for headless servers and I think it is slowly starting to happen for GUI clients, but it will take some time. We developers like Linux, but most of our end users still live and breathe on Windows. Not that I like it, but it's a fact, at least in the commercial field. Joachim
On Wed, Apr 10, 2019 at 6:21 AM jtuchel@objektfabrik.de < jtuchel@objektfabrik.de> wrote:
Richard,
as a comment on VA Smalltalk: you are referring to the Linux version, which is also your Screenshot. I agree that Linux version of VA Smalltalk is far from what I'd call enjoyable or beautiful. If you take a look at the Windows version of VAST, you'll immediately realize that Linux users miss a lot of nice stuff that has been added to VA Smalltalk over the last few releases.
The reason here is most likely that commercial Smalltalk projects mainly target Windows. This has changed for headless servers and I think it is slowly starting to happen for GUI clients, but it will take some time. We developers like Linux, but most of our end users still live and breathe on Windows. Not that I like it, but it's a fact, at least in the commercial field.
Joachim
Hi, I was about to answer same thing. Differently than Pharo, VW etc where the rendering happens inside Smalltalk, in VA Smalltalk, its native. And so, there are differences in the implementations between Unix and Windows. The version in Windows is "much less ugly" than the one on Linux. In the upcoming release we have also added HiDPI, as you can see here: https://twitter.com/MartinezPeck/status/1063432539908571136 And in 9.1, we did fix many UI related things for the Linux flavor, included the shortcuts. If you are still facing issues, please contact us separately (not to spam Pharo list) Best, -- Mariano Martinez Peck Email: marianopeck@gmail.com Twitter: @MartinezPeck LinkedIn: https://www.linkedin.com/in/mariano-mart%C3%ADnez-peck/
Yeah, ok. But please do not take this thread as a way to defend/criticise other dialects (we all know there is a lot of passion around). My intention is more to ask âwhat is cool of dialect X that you would like Pharo to have tooâ or âhow can we make Pharo to be as beautiful and/or enjoyable as you think other dialects areâ. I know this is a very opinionated area. I believe Pharo looks and feels better than most of the other dialects, but Iâm not stupid, I know there are tons of things to improve and I know there are good ideas/implementations around and I want watch them, to see how can improve even more our Pharo. So please, stay cool :P Esteban
On 10 Apr 2019, at 14:06, Mariano Martinez Peck <marianopeck@gmail.com> wrote:
On Wed, Apr 10, 2019 at 6:21 AM jtuchel@objektfabrik.de <mailto:jtuchel@objektfabrik.de> <jtuchel@objektfabrik.de <mailto:jtuchel@objektfabrik.de>> wrote: Richard,
as a comment on VA Smalltalk: you are referring to the Linux version, which is also your Screenshot. I agree that Linux version of VA Smalltalk is far from what I'd call enjoyable or beautiful. If you take a look at the Windows version of VAST, you'll immediately realize that Linux users miss a lot of nice stuff that has been added to VA Smalltalk over the last few releases.
The reason here is most likely that commercial Smalltalk projects mainly target Windows. This has changed for headless servers and I think it is slowly starting to happen for GUI clients, but it will take some time. We developers like Linux, but most of our end users still live and breathe on Windows. Not that I like it, but it's a fact, at least in the commercial field.
Joachim
Hi,
I was about to answer same thing. Differently than Pharo, VW etc where the rendering happens inside Smalltalk, in VA Smalltalk, its native. And so, there are differences in the implementations between Unix and Windows. The version in Windows is "much less ugly" than the one on Linux. In the upcoming release we have also added HiDPI, as you can see here: https://twitter.com/MartinezPeck/status/1063432539908571136 <https://twitter.com/MartinezPeck/status/1063432539908571136> And in 9.1, we did fix many UI related things for the Linux flavor, included the shortcuts. If you are still facing issues, please contact us separately (not to spam Pharo list)
Best,
-- Mariano Martinez Peck Email: marianopeck@gmail.com <mailto:marianopeck@gmail.com> Twitter: @MartinezPeck LinkedIn: https://www.linkedin.com/in/mariano-mart%C3%ADnez-peck/ <https://www.linkedin.com/in/mariano-mart%C3%ADnez-peck/>
I love this attitude coming from the very core of the Pharo dev-team, which felt to me as being blind to what other dialects were doing or did in the past, and these is days seems to be catching up quite quickly. Dolphin Smalltalk: Practically all "widgets" (aka "views") are the native ones, and they behave as expected by a Windows user, both in terms of shortcuts, styling, etc. It feels like a Smalltalk built by Microsoft itself. The MVP approach to build GUIs is, in my experience, the best of all available options, and the way the Presenters and Views are factored is great, for what I could see, Spec 2.0 is going in that direction and I like. Some could say this would restrict you from building "different" apps, but IMO that is another layer that must be built on top of the basic building blocks. It doesn't use pragmas (I particularly don't like them much), but there are "hooks" everywhere to add items to tooling menus, etc. The consistency and coherence of the whole system is outstanding, not only in terms of UI, and I think it is the result of two great developers (and I would argue only one in terms of UI), working for over a decade in refining, trimming and polishing every corner of the app while also using it for their own personal and business developments. Dolphin had both a commercial purpose and a utility purpose, the first as a vendor to fulfill developer needs, but the others for them as a business to develop their own applications. So in the end they were profiting from scratching their own itch. So what I would love to have in Pharo from Dolphin? The UX consistency that a workspace context menu is as similar as the one in the browser code or the one in the Debugger (e.g. Why I can't do an "extract method" refactoring within the debugger?). The concept of a SessionManager is great also, you could "deploy" your image to have a session manager that will handle headless command line application, a full blown UI or even be used an out of process COM server. There are many cons, but we're focusing only in what I'd like. I developed with Dolphin for more than +10 years , building business critical application with it. VisualWorks I use it every day and don't miss much from it, except that the UI is snappier than the current in Pharo. There is no lag the interaction with most widgets. Certain things such as breakpoints and bread and butter things "just work". What I would like in Pharo from VW?: Multiple windows, robust tooling and snappier UI. I don't miss the namespacing, because I understand there are better things in the makings for Pharo :) VisualAge/VAST: I have only used it up to v5.5, but the "Interrupt" button it has worked, I never understood how it was implemented, but no matter how tight the recursion loop was, you hit that "stop everything" button, and everything stopped. For those that don't know, the VAST IDE had an external small window that just had a button, that worked as a panic button to halt the execution of the image. Very much like the [Alt]+[.] of Pharo, but, again, it worked magically. What I would like in Pharo from VAST?: THAT BUTTON. :D Smalltalk/X It always feelt alien to me and it is more an "utility" dialect for themselves that they happened to make public. The nicest thing I found is that it had multiple windows where each window has it's own process! This is very much like Chromium/Chrome works, where you can kill a single tab and keep the other tabs working. What I would like: That capability, although I think this would require an overhaul of the current VM. Cuis Smalltalk: It is the most "approachable" of the Squeak spin-offs, it feels like the most "Dolphin like" of the them as in it is the only that can be understood as a whole by a single person and whose tools can be learnt by inference. They recently added LiveTyping and other "live info" capabilities <https://twitter.com/HernanWilkinson/status/1087325709289357312> than, AFAIU, can be easily added to Pharo as well as long as they add a few extensions to the VM. What I would like: LiveTyping and friends. Summarizing: There are many things out there, but even so, I find Pharo the most enjoyable of all existing dialects, and everyday when I come back to it to work on some personal project I notice how far it has gone from most of the above. But sometimes I enjoy it as I enjoy working out or playing golf: I enjoy it but not without effort and some pain from my side, maybe I finish the day saying I need to find an alternative and then the next day I'm there wanting to use it again. :) Regards, Esteban A. Maringolo El mié., 10 abr. 2019 a las 3:26, Esteban Lorenzano (<estebanlm@gmail.com>) escribió:
Hi,
Time to time I hear people like Richard saying âDolphin is the dialect most beautiful Smalltalk he usedâ and others praising it in different levels. As Pharo âarchitectâ (or whatever I am, but at least Iâm sure I have to pay attention to the IDE :P), Iâm interested to know what elements of Dolphin dialect you find âbeautifulâ, âenjoyableâ and productive. What it is?
- the MVP? - integration with Windows? The way this integration is done? (If so⦠how is it done?) â¦
I am very interested on knowing this with some detail level. That doesnât mean I will react and do something, but I want to have a better understanding and put it in my radar to take inspiration to enhance the Pharo experience :P
participants (7)
-
Esteban Lorenzano -
Esteban Maringolo -
jtuchel＠objektfabrik.de -
K K Subbu -
Mariano Martinez Peck -
Richard O'Keefe -
Roelof Wobben