April 2020 - Pharo-users - lists.pharo.org

Re: [Pharo-users] mentor question 4

by Roelof Wobben

April 30, 2020

Fwd: Statement about the VM

by ducasse

> Begin forwarded message: > > From: StÃ©phane Ducasse <stephane.ducasse(a)inria.fr> > Subject: Statement about the VM > Date: 27 April 2020 at 18:06:09 CEST > To: Any question about pharo is welcome <pharo-users(a)lists.pharo.org>, Pharo Development List <pharo-dev(a)lists.pharo.org> > > As promised the consortium engineering team composed of G. Polito, P. Tesone, E. Lorenzano, M. Denker, C. Demarey and S. Ducasse > produced a statement about the Pharo VM. This statement was reviewed by the Pharo board and follows decisions taken during the > 2019 consortium general assembly held during PharoDays. > > S. Ducasse on the behalf of the consortium > > > > > > > > -------------------------------------------- > StÃ©phane Ducasse > http://stephane.ducasse.free.fr <http://stephane.ducasse.free.fr/> / http://www.pharo.org <http://www.pharo.org/> > 03 59 35 87 52 > Assistant: Julie Jonas > FAX 03 59 57 78 50 > TEL 03 59 35 86 16 > S. Ducasse - Inria > 40, avenue Halley, > Parc Scientifique de la Haute Borne, BÃ¢t.A, Park Plaza > Villeneuve d'Ascq 59650 > France >

April 30, 2020

Re: [Pharo-users] mentor question 4

by Ben Coman

On Thu, 30 Apr 2020 at 16:46, Roelof Wobben via Pharo-users < pharo-users(a)lists.pharo.org> wrote: > Op 30-4-2020 om 10:31 schreef Ben Coman: > > collection := '8569 2478 0383 3437'. > > (collection reverse selectWithIndex: [:item :index | (index % 2 == 0) > > ifTrue: [item *2]] ) inspect > > > I see a error and the non-even numbers are nill now. > > but after some figgeling this seems to work : > Great that you worked it out for yourself !!! "figgeling" is a very important part of programming. > > collection := '8569247803833437' asArray. > checkNumber := (collection reverse withIndexCollect: [:item :index | > (index % 2 == 0) ifTrue: [item asInteger *2] ifFalse: [item asInteger]] > ) sum inspect > ^ checkNumber isDivisibleBy: 10 > That looks like it would work, but the inspect is redundant now you know how it works. An important take away from this is that when you are confused by what is happening, you need to LOOK at each spot you data is transformed, where "inspect" is your friend, particular running it from the debugger. -------------------------------- Now there is another path you might try, but first I want to stress that I didn't know this answer a minute ago - I only just discovered it !! So this answer is not based on something magic I knew directly, but on my approach to guess, search and test within the system. I was considering how you were dealing with "every second digit" and considered a general description of this was "pairs". I _wondered_ whether Pharo had any methods dealing with "pairs" ? Spotter is a good place to ask this question, so I... Pressed <Shift-Enter> Typed... pair #i to see if there were any implementors containing the word "pair" and discovered SequenceableCollection>>#pairsCollect: 3. First time I've seen that method, I wonder how it works? The method comment gives a clue that the block takes two arguments. So lets try-the-simplest-possible-thing... ( '123456' pairsCollect: [ :a :b | a ] ) inspect ==> #($1 $3 $5) So that looks useful. Try experimenting with it yourself. cheers -ben

April 30, 2020

Re: [Pharo-users] mentor question 4

by Roelof Wobben

Op 30-4-2020 om 10:31 schreef Ben Coman: > collection := '8569 2478 0383 3437'. > (collection reverse selectWithIndex: [:item :index | (index % 2 == 0) > ifTrue: [item *2]] )Â inspect I see a error and the non-even numbers are nill now. but after some figgeling this seems to work : collection := '8569247803833437'asArray. checkNumber := (collection reverse withIndexCollect: [:item :index | (index % 2 == 0) ifTrue: [item asInteger *2] ifFalse: [item asInteger]] ) sum inspect ^ checkNumber isDivisibleBy: 10

April 30, 2020

Re: [Pharo-users] mentor question 4

by Ben Coman

On Thu, 30 Apr 2020 at 14:33, Roelof Wobben via Pharo-users < pharo-users(a)lists.pharo.org> wrote: > Hello, > > I hope I can discuss my approch to this problem : > > Given a number determine whether or not it is valid per the Luhn formula. > > The Luhn algorithm <https://en.wikipedia.org/wiki/Luhn_algorithm> is a > simple checksum formula used to validate a variety of identification > numbers, such as credit card numbers and Canadian Social Insurance Numbers. > > The task is to check if a given string is valid. > Validating a Number > > Strings of length 1 or less are not valid. Spaces are allowed in the > input, but they should be stripped before checking. All other non-digit > characters are disallowed. > Example 1: valid credit card number > > 4539 1488 0343 6467 > > The first step of the Luhn algorithm is to double every second digit, > starting from the right. We will be doubling > > 4_3_ 1_8_ 0_4_ 6_6_ > > If doubling the number results in a number greater than 9 then subtract 9 > from the product. The results of our doubling: > > 8569 2478 0383 3437 > > Then sum all of the digits: > > 8+5+6+9+2+4+7+8+0+3+8+3+3+4+3+7 = 80 > > If the sum is evenly divisible by 10, then the number is valid. This > number is valid! > > > my idea was to do these steps > > 1) reverse the input. > 2) use this to double every second digit and calculate the sum of all > the numbers : > > checkNumber := (collection reverse selectwith index: [:item :index | > (index % 2 == 0) . IfTrue: [item *2]] ) sumNumbers > I just want to check that before you are ask such questions, did you actually run this code? Because it would be fairly easy to see how close you are by evaluating it without #sumNumbers. i.e Please report what you see when evaluating this.... ``` collection := '8569 2478 0383 3437'. (collection reverse selectWithIndex: [:item :index | (index % 2 == 0) ifTrue: [item *2]] ) inspect ``` 3) check if its a valid number by doing this : > > > ^ (checkNumber % 10 == 0) > That would work, but there is a more intention revealing method... #isDivisibleBy: cheers -ben

April 30, 2020

mentor question 4

by Roelof Wobben

April 30, 2020

Re: [Pharo-users] mentor question 3 is there a formula for this

by Richard Sargent

On Wed, Apr 29, 2020 at 11:30 AM Roelof Wobben <r.wobben(a)home.nl> wrote: > Am I right here or terrible wrong ? > If you are referring to calculating the size of the square, you are correct. > Roelof > > > > Op 28-4-2020 om 20:53 schreef Roelof Wobben: > > Thanks, > > And the 5 can also be calculated by 2 * (char - $a) + 1 > > Roelof > > > > Op 28-4-2020 om 18:31 schreef Richard Sargent: > > Formula? Well, it's pretty straight forward. > > Let's start with the size of the diamond (it field, actually). In the > example, there are two lines above and two lines below the "C" line. > C-A = 2. This number looks useful. > The dimension is 2+1+2 square. > > Yes. That is what I wrote. > > How many spaces before a letter? C-letter i.e. C-A = 2 C-B = 1 and C-C = 0 > The same number of spaces after the second/last occurrence of the letter > on the line. > The number of spaces between the letters on a line is the size minus the > number of spaces before and after plus the two copies of the current line's > letter. For the "B" line, there is one space before and after, 2x"B", > leaving 5 - 1 -1 - 2 = 1 space between. For the "A" line, the simple > arithmetic would give you -1, which also confirms that just one "A" is > appropriate with no space between first and last letter on the line. (For > "A", it is first and last, once only.) > > After that, you just need to iterate ($A to: $C), ($(C-1) to: $A by: -1) > and do the arithmetic. > > > On Tue, Apr 28, 2020 at 1:23 AM Roelof Wobben via Pharo-users < > pharo-users(a)lists.pharo.org> wrote: > >> Hello, >> >> I try now to solve this one : >> >> ntroduction >> >> The diamond kata takes as its input a letter, and outputs it in a diamond >> shape. Given a letter, it prints a diamond starting with 'A', with the >> supplied letter at the widest point. >> Requirements >> >> - The first row contains one 'A'. >> - The last row contains one 'A'. >> - All rows, except the first and last, have exactly two identical >> letters. >> - All rows have as many trailing spaces as leading spaces. (This >> might be 0). >> - The diamond is horizontally symmetric. >> - The diamond is vertically symmetric. >> - The diamond has a square shape (width equals height). >> - The letters form a diamond shape. >> - The top half has the letters in ascending order. >> - The bottom half has the letters in descending order. >> - The four corners (containing the spaces) are triangles. >> >> Examples >> >> In the following examples, spaces are indicated by Â· characters. >> >> Diamond for letter 'A': >> >> A >> >> Diamond for letter 'C': >> >> Â·Â·AÂ·Â· >> Â·BÂ·BÂ· >> CÂ·Â·Â·C >> Â·BÂ·BÂ· >> Â·Â·AÂ·Â· >> >> >> I noticed that if you take a quarter of it. you see this pattern >> >> 001 >> 010 >> 100 >> >> where a 0 is a space and a 1 is the character. >> >> Is there a easy way to make some sort of formula so I can make a output of this ? >> >> >> Roelof >> >> >> > >

April 29, 2020

Re: [Pharo-users] mentor question 3 is there a formula for this

by Roelof Wobben

April 29, 2020

Re: [Pharo-users] mentor question 3 is there a formula for this

by Ben Coman

Building on Richard's advice, one way to break this down into a series of simpler tasks is - first generate a square without any dots, i.e. ALL A's on the first line, ALL B's on second line, ALL C's on third line. - second, work out when to output a dot rather than a letter. cheers -ben On Wed, 29 Apr 2020 at 00:32, Richard Sargent < richard.sargent(a)gemtalksystems.com> wrote: > Formula? Well, it's pretty straight forward. > > Let's start with the size of the diamond (it field, actually). In the > example, there are two lines above and two lines below the "C" line. > C-A = 2. This number looks useful. > The dimension is 2+1+2 square. > > How many spaces before a letter? C-letter i.e. C-A = 2 C-B = 1 and C-C = 0 > The same number of spaces after the second/last occurrence of the letter > on the line. > The number of spaces between the letters on a line is the size minus the > number of spaces before and after plus the two copies of the current line's > letter. For the "B" line, there is one space before and after, 2x"B", > leaving 5 - 1 -1 - 2 = 1 space between. For the "A" line, the simple > arithmetic would give you -1, which also confirms that just one "A" is > appropriate with no space between first and last letter on the line. (For > "A", it is first and last, once only.) > > After that, you just need to iterate ($A to: $C), ($(C-1) to: $A by: -1) > and do the arithmetic. > > > On Tue, Apr 28, 2020 at 1:23 AM Roelof Wobben via Pharo-users < > pharo-users(a)lists.pharo.org> wrote: > >> Hello, >> >> I try now to solve this one : >> >> ntroduction >> >> The diamond kata takes as its input a letter, and outputs it in a diamond >> shape. Given a letter, it prints a diamond starting with 'A', with the >> supplied letter at the widest point. >> Requirements >> >> - The first row contains one 'A'. >> - The last row contains one 'A'. >> - All rows, except the first and last, have exactly two identical >> letters. >> - All rows have as many trailing spaces as leading spaces. (This >> might be 0). >> - The diamond is horizontally symmetric. >> - The diamond is vertically symmetric. >> - The diamond has a square shape (width equals height). >> - The letters form a diamond shape. >> - The top half has the letters in ascending order. >> - The bottom half has the letters in descending order. >> - The four corners (containing the spaces) are triangles. >> >> Examples >> >> In the following examples, spaces are indicated by Â· characters. >> >> Diamond for letter 'A': >> >> A >> >> Diamond for letter 'C': >> >> Â·Â·AÂ·Â· >> Â·BÂ·BÂ· >> CÂ·Â·Â·C >> Â·BÂ·BÂ· >> Â·Â·AÂ·Â· >> >> >> I noticed that if you take a quarter of it. you see this pattern >> >> 001 >> 010 >> 100 >> >> where a 0 is a space and a 1 is the character. >> >> Is there a easy way to make some sort of formula so I can make a output of this ? >> >> >> Roelof >> >> >>

April 29, 2020

Re: [Pharo-users] can I divide a string into part of exactly n length

by Ben Coman

On Tue, 28 Apr 2020 at 01:08, Roelof Wobben via Pharo-users < pharo-users(a)lists.pharo.org> wrote: > Op 27-4-2020 om 19:05 schreef Richard Sargent: > > On Mon, Apr 27, 2020 at 9:27 AM Roelof Wobben via Pharo-users < > pharo-users(a)lists.pharo.org> wrote: > >> Hello, >> >> I wonder if it is possible in Pharo to divide a string in lets say part >> of 3. >> so this : 'abcdefgh' >> >> would be 'abc def gh` >> > > Do you really want a single string with spaces inserted or do you want a > collection of substrings, each three characters (or less, for the last one)? > > > I need a single string with spaces inserted. > So maybe I have formulate my question wrong. Very difficult if English is > not your mother language and you were bad at school in languages a very > very long ago. > I didn't previously know of a method to do this, but I "guessed" what you needed might be related to "grouping", so I did... 'abcd' inspect. then in the Meta tab, starting at Collection, filtered on.... group* and worked up the hierarchy discovering #groupsOf:atATimeDo: in SequenceableCollection, which guesswork found could work like this... ``` input := 'abcdefghijk'. stream := String streamContents: [:s | input groupsOf: 3 atATimeDo: [ :group | s nextPutAll: group; nextPutAll: ' ']]. stream contents inspect. ``` One of the skills a new programmer needs to develop is to make those educated "guesses" and know where/how to test them. So I learnt a new method today. thx. cheers -ben

April 29, 2020