---------- Forwarded message ---------- From: Eliot Miranda <eliot.mira...@gmail.com> Date: 2009/12/16 Subject: Re: [BUG] [ :a | ] value: 1 To: Lukas Renggli <reng...@gmail.com>, Dan Ingalls <dan.inga...@sun.com>, "L. Peter Deutsch" <l...@major2nd.com> Cc: The general-purpose Squeak developers list <squeak-...@lists.squeakfoundation.org>
Hi Lukas, can you forward my response to Pharo? TIA. On Wed, Dec 16, 2009 at 2:54 AM, Lukas Renggli <reng...@gmail.com> wrote: > > Hi Eliot > > While working on a way to use the RB-AST with the standard compiler I > think I found a problem in your code. To reproduce evaluate the > following expression: > > [ :a | ] value: 1 > > According to my understanding that should return nil, not the first argument > 1. > > The generated bytecode is: > > pushTemp: 0 > blockReturn > > I think it should be: > > pushConstant nil > blockReturn > > Cheers, > Lukas :) :) This is funny. VisualWorks has exactly the same bug^H^H^Hfeature. And if you look at the ANSI standard (ok, this is from the draft, but it is essentially the actual document) there is an exception for precisely this case, See the last sentence in section 3.4.4 Blocks: If a block has no <block body> or no <statements> in its <block body> then the value of the block is undefined. Which allows [] to be implemented as e.g. [Random new next]. In fact both VisualWorks and Squeak answer the last argument: [:a ] value: 1 1 [:a :b|] value: 1 value: 2 2 [:a :b :c :d :e :f :g :h| ] valueWithArguments: (1 to: 8) 8 [:a | nil] value: 1 nil [:a :b| nil] value: 1 value: 2 nil At least it is consistent whether the block is inlined or not ;) 1+2 ifNotNil: [:arg|] 3 It as ever been so. This from Smalltalk-80 V2: BlockNode methods for initialize-release arguments: argNodes statements: statementsCollection returns: returnBool from: encoder sourceEnd: sourceEnd "compile" sourceRange _ sourceEnd to: sourceEnd. arguments _ argNodes. statements _ statementsCollection size > 0 ifTrue: [statementsCollection] ifFalse: [argNodes size > 0 ifTrue: [statementsCollection copyWith: arguments last] ifFalse: [Array with: NodeNil]]. returns _ returnBool This from VW: BlockNode methods for code generation emitBody: codeStream "The codeStream invokes this to compile the body of the block, including the final return." (body isEmpty and: [arguments isEmpty not]) ifTrue: [codeStream noteSourceStart: body. arguments last variable emitLocalReturn: codeStream from: body] ifFalse: [body emitLocalReturn: codeStream from: body] This from Squeak (my timestamp, but I just changed the _'s to :='s :) ) BlockNode methods for initialize-release arguments: argNodes statements: statementsCollection returns: returnBool from: encoder "Compile." arguments := argNodes. statements := statementsCollection size > 0 ifTrue: [statementsCollection] ifFalse: [argNodes size > 0 ifTrue: [statementsCollection copyWith: arguments last] ifFalse: [Array with: NodeNil]]. optimized := false. returns := returnBool So at least it is easy to fix ;) The question you have to ask yourself is how much code is affected by this wafer thin change. I'm with you, I think this is a bug. But perhaps it was well thought through. What say you, Dan & Peter? Did y'all agonise over this? What say you Squeak & Pharo communities? Should we fix this or make it a preference ;) best Eliot P.S. I'm caught between wanting to fix it and wanting to let sleeping dogs lie. I'd like to know what all the other dialects do. If a substantial majority have the same curio I think we have to live with this, uh, ornament. Just to be clear, making it a preference is a sick joke on my part. > > -- > Lukas Renggli > http://www.lukas-renggli.ch -- Lukas Renggli http://www.lukas-renggli.ch _______________________________________________ Pharo-project mailing list Pharo-project@lists.gforge.inria.fr http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project
