There is no agreement between Smalltalk systems about how to compare block contexts for equality. In Smalltalk-80 (and I have two versions of Smalltalk-80 to compare), block equality is identity. The same in VisualAge Smalltalk 8.6.3. The same in GNU Smalltalk. The same in Smalltalk/X-JV. Squeak has a similar definition to VW. My reading of the ANSI standard is that it is carefully vague about this.
Equality of functions has been troublesome for decades. Haskell: bans it. Standard ML: bans it. Some other ML-family languages: it's a run-time error. Lisp family: varies. Interlisp says nothing. Scheme gives lower and upper bounds. Imagine a Smalltalk that recognises [<literal>] blocks and allocates one static closure per <literal>. Then [true] == [true] hence [true] = [true] even when the two <block constructor>s were in different methods. The Squeak and VW definitions would regard them as unequal. (This is on my TODO list, principally for [] [true] [false] and [0].) For the special case of [], you don't *have* to imagine it. If I'm reading VAST correctly, it treats "empty blocks" specially. If you *rely* on the definition of #= for block contexts/closures you are almost certainly doing something dangerous. You are certainly doing something that is not portable. On Thu, 13 Apr 2023 at 18:55, Steffen Märcker <merk...@web.de> wrote: > Hi! > > In VisualWorks, blocks can be compared with each other. In Pharo the > comparison just checks for Identity. Is this on purpose? For reference, > that's how BlockClosure>>= is implemented in VW: > > > = aBlockClosure > ^aBlockClosure class = self class and: > [method = aBlockClosure method and: > [outerContext = aBlockClosure outerContext and: > [copiedValues = aBlockClosure copiedValues]]] > > Kind regards, > Steffen >
