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.