April 2019 - Pharo-users - lists.pharo.org

Re: [Pharo-users] is this valid smalltalk

by Richard O'Keefe

For a change this is an exercism problem I know something about. I did look at the exercism web site, and did all the SML exercises, but could not find any for Smalltalk or Pharo. The exercise is in fact about using a stack. stack <- empty for each character of the string if it is one of ( [ { push it on the stack if it is one of ) ] } if the stack is empty or the top element does not correspond to this character, return false if it is not one of ( ) [ ] { } just ignore it return (the stack is empty) BOTH of the "return" constructs in this pseudo-code become ^ something in Smalltalk. "Long returns", where "^" occurs inside a block, are well defined, very useful, and universally accepted in Smalltalk. There is no analogue of "^" for returning from a block. By the way, this has nothing to do with #do:. It's about returning from the method through any number of blocks. For example, you will sometimes see code like x := aDictionary at: aKey ifAbsent: [^false]. On Fri, 5 Apr 2019 at 00:16, Roelof Wobben <r.wobben(a)home.nl> wrote: > Hello, > > For a challenge of Exercism I need to check if some parenthes and > brackets are balanced. > > so for example > > () = true > ([]) = true > > but (]) is not true because the bracket has no opening bracket. > > Now I wonder if I can premature end a #do: like this > > collection do: [:element | (condition with element) ifFalse: [^false]] > > in pseudo code > > is this a valid way to end the do ? > or is there a better way ? > > Roelof > >

April 4, 2019

Re: [Pharo-users] FFIExternalStructureReferenceHandle and pushing it to the stack

by Holger Freyther

> On 4. Apr 2019, at 08:36, Holger Freyther <holger(a)freyther.de> wrote: And I have a stand-a-lone testcase for Pharo as well: https://github.com/zecke/pharo/commit/390f81241a7dfee546784453fa426bc1c218b… Any hint of how I can test (simulate?) and generate changes to ThreadedX64SysVFFIPlugin from Pharo (or how you normally do it in Squeak). cheers holger > In addition to my mail from yesterday to vm-dev I want to share the following example to illustrate the problem. I have taken StructA and StructNested from the FFIExternalStructureReferenceHandle class comment and put it into Unclassified.st that is attached to this mail. I am also making a call to LibC's getpid and try to push StructNested to the stack. The ffiCall is failing before getpid is called (Bad argument to external function). > > The reproducer is: > > StructA new theNest anyCall. > > > StructA has a ByteArray handle of the full struct. theNest returns an instance of StructNested with a FFIExternalStructureReferenceHandle. This makes sense as well. It can't be a copy of the ByteArray (or else updates would be invisible to the outer struct) and it can't be an ExternalAddress as StructA's handle might move in the Smalltalk heap. > > I am not entirely sure how this is should work but what do you think of: > > 1st) Extending ExternalStructure class comment to list FFIExternalStructureReferenceHandle as possible handle type? I think we would only describe the reality. > > > 2nd) ThreadedFFIPlugin>>#ffiPushStructureContentsOf: should be aware of FFIExternalStructureReferenceHandle and know how to reach the handle. Or should there be something in the image converting this to a ByteArray when being pushed as value in a ffiCall? > > > comments/ideas? > > > <Unclassified.st>

April 4, 2019

Re: [Pharo-users] is this valid smalltalk

by Herby VojÄÃk

On 4. 4. 2019 13:16, Roelof Wobben wrote: > Hello, > > For a challenge of Exercism I need to check if some parenthes and > brackets are balanced. > > so for example > > ()Â = true > ([])Â = true > > but (])Â is not true because the bracket has no opening bracket. > > Now I wonder if I can premature end a #do:Â like this > > collection do: [:element | (condition with element) ifFalse: [^false]] > > in pseudo code > > is this a valid way to end the do ? Not sure I understand your question properly, but yes, you can do this, it is called "non-local return" and is a known pattern in Smalltalk. > or is there a better way ? (collection detect: [:element | (condition with element) not] ifNone: [sentinel]) == sentinel ifFalse: [ ^false ] for example does not force you to employ it, as well as (collection allSatisfy: [:element | (condition with element)]) ifFalse: [ ^false ] > > Roelof Herby

April 4, 2019

Re: [Pharo-users] is this valid smalltalk

by Roelof Wobben

Op 4-4-2019 om 13:22 schreef K K Subbu: > On 04/04/19 4:46 PM, Roelof Wobben wrote: >> Hello, >> >> For a challenge of Exercism I need to check if some parenthes and >> brackets are balanced. >> >> so for example >> >> ()Â = true >> ([])Â = true >> >> but (])Â is not true because the bracket has no opening bracket. >> >> Now I wonder if I can premature end a #do:Â like this >> >> collection do: [:element | (condition with element) ifFalse: [^false]] > > Have you looked at anySatisfy: > > Â #('the' 'quick' 'brown' 'fox') anySatisfy: [:s | s beginsWith: 'x' ] > > Regards .. Subbu > yep,Â i alsoÂ took a look at that one

April 4, 2019

Re: [Pharo-users] is this valid smalltalk

by K K Subbu

On 04/04/19 4:46 PM, Roelof Wobben wrote: > Hello, > > For a challenge of Exercism I need to check if some parenthes and > brackets are balanced. > > so for example > > ()Â = true > ([])Â = true > > but (])Â is not true because the bracket has no opening bracket. > > Now I wonder if I can premature end a #do:Â like this > > collection do: [:element | (condition with element) ifFalse: [^false]] Have you looked at anySatisfy: #('the' 'quick' 'brown' 'fox') anySatisfy: [:s | s beginsWith: 'x' ] Regards .. Subbu

April 4, 2019

is this valid smalltalk

by Roelof Wobben

Hello, For a challenge of Exercism I need to check if some parenthes and brackets are balanced. so for example ()Â = true ([])Â = true but (])Â is not true because the bracket has no opening bracket. Now I wonder if I can premature end a #do:Â like this collection do: [:element | (condition with element) ifFalse: [^false]] in pseudo code is this a valid way to end the do ? or is there a better way ? Roelof

April 4, 2019

Re: [Pharo-users] Slots and Metalink

by Marcus Denker

> On 3 Apr 2019, at 15:57, Vitor Medina Cruz <vitormcruz(a)gmail.com> wrote: > > Hello, > > Is it possible to intercept a slot store? I tried with a before metalink into #write:to selector, but it don't seems to work. Should I use another selector? > The #write:to: method is the reflective read method that implements read on the level of the variable. If you subclass class Slot, you can make you own kind of Variables by just overriding #write:to and read: But of course compiling every read by calling a method would be very slow. Therefore, one can override emitStore: and emitValue: to instead emit faster code by telling the compiler exactly what bytecode to generate for read and write. This makes it much faster, but at the expense that the reflective methods are not called anymore. (It would be nicer if we would inline the read: code automatically, but that has its own set of problems) > I would like to experiment with ivar change notification, but I don't know what is the better approach. > What you could do is to make your own subclass to experiment. IndexedSlot is the superclass of the normal instancevariables, but without the optimised code generation. So it is the perfect superclass to experiment: IndexedSlot subclass: #MyTestSlot instanceVariableNames: '' classVariableNames: '' package: 'Slot-Core-Variablesâ now Implement read: anObject Transcript show: 'reading ', self name. super read: anObject. Now we can make a class that uses it: Object subclass: #MyClass slots: { #ivar => MyTestSlot } classVariables: { } package: 'Slot-Core-Variablesâ and add a simple method reading the variable: ivar ^ivar If you now execute "MyClass new ivarâ and you will see the output on the Transcript. Marcus

April 4, 2019

FFIExternalStructureReferenceHandle and pushing it to the stack

by Holger Freyther

In addition to my mail from yesterday to vm-dev I want to share the following example to illustrate the problem. I have taken StructA and StructNested from the FFIExternalStructureReferenceHandle class comment and put it into Unclassified.st that is attached to this mail. I am also making a call to LibC's getpid and try to push StructNested to the stack. The ffiCall is failing before getpid is called (Bad argument to external function). The reproducer is: StructA new theNest anyCall. StructA has a ByteArray handle of the full struct. theNest returns an instance of StructNested with a FFIExternalStructureReferenceHandle. This makes sense as well. It can't be a copy of the ByteArray (or else updates would be invisible to the outer struct) and it can't be an ExternalAddress as StructA's handle might move in the Smalltalk heap. I am not entirely sure how this is should work but what do you think of: 1st) Extending ExternalStructure class comment to list FFIExternalStructureReferenceHandle as possible handle type? I think we would only describe the reality. 2nd) ThreadedFFIPlugin>>#ffiPushStructureContentsOf: should be aware of FFIExternalStructureReferenceHandle and know how to reach the handle. Or should there be something in the image converting this to a ByteArray when being pushed as value in a ffiCall? comments/ideas?

April 4, 2019

FFI and when to convert the stack pointer (an Alien) into an ExternalAddress

by Holger Freyther

I am toying with Ben's bindings to clang-c (C interface to the Clang C-indexer API). One of the main features of the C API is a way to visit the translation unit. This is implemented as a callback into Smalltalk with with "cursors" providing indirect access and simplified access to the node of the AST. The return result indicates how to continue the traversal (continue, stop, recurse). FFICallback signature: #( CXChildVisitResult ( CXCursor cursor, CXCursor parent, CXString client_data)) block: [ :cursor :parent :clientData | cursor spelling. <- booom but no crash aCXChildVisitResult value "@1" ]. "cursor" will be an Instance of CXCursor and is passed by value and the C struct size is >16 bytes (on Unix this is passed on the stack). The resulting CXCursor has a handle that is invalid to perform any call-out with. CXCursor getHandle FFIExternalStructureReferenceHandle handle: an Alien (isPointer = true, the stack ptr offset: 0 ExternalStructure defines valid types as ByteArray (the data) or ExternalAddress (the pointer). FFIExternalStructureReferenceHandle is missing there and I will create a separate thread/ticket about it. So somewhere from: FFICallback>>#valueWithContext:sp: ... FFICallbackArg>>#extractStructType: FFIExternalType>>#handle:at: FFIExternalStructureType>>#basicHandle:at: ee will need to convert the handle + offset (one based) to an ExternalAddress. Now the protocol of >>#handle:at: and >>#integerAt:, >>#pointerAt: indicate that we want to carry address+offset into late of the conversion. And I can't point my finger into where it should be done. I have created: Alien>>#referenceStructAt: byteOffset length: length ^self isPointer ifFalse: [super referenceStructAt: byteOffset length: length ] ifTrue: [ (ExternalAddress fromAddress: self addressField) + (byteOffset - 1)] This "fixes" it. But that is at the last point in the conversion. It shadows another problem as well. So in fact maybe changing: FFICallbackArgumentReader>>#extractPointerOfType: and >>#extractStructType: to read: ... pair := self nextBaseAddressForStructure: type. baseAddressToRead := ExternalAddress fromAddress: pair first address. <- modified offsetOfBaseAddress := pair second. ... is this the right way forward? We convert the stack to an ExternalAddress early on and use it. With the above change to FFICallbackArgumentReader the CXCursor from the stack will read as: CXCursor getHandle FFIExternalStructureReferenceHandle handle: ExternalAddress offset: 0 I am still not able to push this cursor to the stack. But that is for another mail. WDUT? holger

April 4, 2019

Difficulties setting up default image in XMonad

by Vanessa McHale

Hi all, When I try to launch the latest Pharo image in XMonad, I run into the following: Pharo launch failure screenshot I couldn't copy the error text unfortunately so I have attached a screenshot instead. Any hints on what might be causing it? Is it due to my using a tiling window manager? Cheers, Vanessa McHale

April 4, 2019