Le lun. 19 août 2019 à 03:37, John Pfersich via Squeak-dev <
squeak-dev at lists.squeakfoundation.org> a écrit :

> The full definition from the draft standards (don’t have the standard
> handy) is:
>
> <block constructor> ::= '[' <block body> ']'
> <block body> ::= [<block argument>* '|'] [<temporaries>] [<statements>]
> <block argument> ::= ':' identifier
>
> The last line is on the next page of the draft.
>
> /————————————————————/
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> On Aug 18, 2019, at 12:09, JOHN SARKELA via Squeak-dev <
> squeak-dev at lists.squeakfoundation.org> wrote:
>
> The ANSI standard has the following rules for blocks:
>
> <block constructor> ::= '[' <block body> ']'
> <block body> ::= [<block argument>* '|'] [<temporaries>] [<statements>]
> The standard does not recognize [:x] as legal syntax for a
> block.<page21image64736448.png> <page21image37471328.png>
> <page21image64735680.png> <page21image64733952.png>
> <page21image64746816.png>
>
> Yes, same as blue book. (block temporaries apart, this did not exist in
st-80), bar is mandatory.

> On Aug 18, 2019, at 3:03 PM, Levente Uzonyi <leves at caesar.elte.hu> wrote:
>
> Hi Nicolas,
>
> Thanks for investigating this.
>
> It's been a pretext for playing with historical material ;)

>
> I still think that it's just a parser bug, which is accidentally "used"
> sometimes, especially because it only works when the block is empty.
>
> Seeing the code, it's the & (hereType ~~ #rightBracket) condition
following (t1 size > 0 which makes [:x ] syntax possible.
Since it has been added explicitely, my bet is that it has been added
purposely and deliberataly rather than accidentally.

It seems [:x ] was not accepted in earlier version 00:

[block | blk argNodes argument |
	 " '[' {:var.} (:var|statements) ']'   BlockNode"
	argNodes ← (Vector new: 1) asStream.
	(self match: #leftBracket)
	  ifTrue:
		[[(self match: #colon) and: [((argument ← self match: #word)
		  ifTrue: [argNodes next← encoder autoBind: argument]
		  ifFalse: [↑self expected: 'Argument name'])]] whileTrueDo: [].
		(argNodes empty or: [(self match: #verticalBar)])   false
		  ifTrue: [↑self expected: 'Vertical bar'].
		((blk ← self statements: argNodes contents doit: false) and: [(self
match: #rightBracket)])
		  ifTrue: [↑blk].
		↑self expected: 'Period or right bracket']
	  ifFalse: [↑self expected: 'Left bracket']].

http://xeroxalto.computerhistory.org/Indigo/BasicDisks/Smalltalk14.bfs!1_/.st80sources.v00.html

>
> Or does it work in other dialects with non-empty blocks?
>
>
Nope, the syntax is only for empty blocks.
It could have worked for any block if we wanted to, because that vertical
bar is just a decoration in blocks.
>From disambiguation POV, it's absolutely unecessary, the block arguments
are already delimited by colon prefix :x
Symetrically, we don't use such delimitation between method pattern and
statements... But it evolved across history:

Historically, Smalltalk-76 did use a single (optional) bar for declaring
temporaries (if any):
methodDefnition := pattern [ '|' temporaries ] '[' statements ']'

Then early Smalltalk-80 method definitions did use empty temps
systematically '[' pattern '|' '|' statements ']'
The two bars were mandatory at that time

"374" LADParser$'Parser'
[temporaries | vars |
	 "[ '|' {variable} ]   {variable, ..., variable}"
	(self match: #verticalBar) and: [((self match: #verticalBar)
	  ifTrue: [↑#()].
	vars ← (Vector new: 8) asStream.
	[hereType   #word] whileTrueDo: [vars next← encoder bind: self advance].
	(self match: #verticalBar)
	  ifTrue: [↑vars contents])].
	↑self expected: 'Vertical bar'].

http://xeroxalto.computerhistory.org/Indigo/BasicDisks/Smalltalk14.bfs!1_/.st80sources.v00.html

I guess that current block syntax is the legacy from all these syntax
evolutions/experiments...

Personnally, I like the bar, because it reminds me mathematical notation I
learned at school for ensemble comprehension
https://fr.wikipedia.org/wiki/Ensemble...

     {x ∊ E | x even }

translated in Smalltalk:

    E select: [:x | x even].

without bar, I'm really NOT used to it:

    E select: [:x x even].


> Is it used in other dialects?
>
> It is used in Squeak:

Context>>runSimulated: aBlock
     "Simulate the execution of the argument, current. Answer the result it
    returns."

     ^ thisContext sender
     runSimulated: aBlock
     contextAtEachStep: [:ignored]

     "Context runSimulated: [Pen new defaultNib: 5; go: 100]"

See also MCMcdReader>>#loadPatch MCPatch>>#initializeWithBase:target:

I also see two usages in VW, MethodContext>>#selector and
BlockContext>>#selector.
The fact that these two methods still have undescore (left arrow)
assignment in source code and have same argument signature [:ignored]
speaks for itself!!!
I'm convinced that it's been an easy hack/feature originating in early 80s
(probably by Dan Ingalls), and forgotten since, that never made it into the
offical specifications.
Smalltalk is malleable enough :)

We can deprecate it if we want, but we will have to support backward
compatibility in the Parser. The boring side of frozen specs...
In this case,we'd better not support it in Shout.

Levente
>
> On Sun, 18 Aug 2019, Nicolas Cellier wrote:
>
> Le jeu. 15 août 2019 à 12:21, Levente Uzonyi <leves at caesar.elte.hu> a
> écrit :
>      On Thu, 15 Aug 2019, Tobias Pape wrote:
>
>      >
>      >> On 15.08.2019, at 03:29, Levente Uzonyi <leves at caesar.elte.hu>
> wrote:
>      >>
>      >> On Wed, 14 Aug 2019, commits at source.squeak.org wrote:
>      >>
>      >>> A new version of ShoutCore was added to project The Inbox:
>      >>> http://source.squeak.org/inbox/ShoutCore-ct.69.mcz
>      >>>
>      >>> ==================== Summary ====================
>      >>>
>      >>> Name: ShoutCore-ct.69
>      >>> Author: ct
>      >>> Time: 14 August 2019, 10:43:04.7164 pm
>      >>> UUID: 7d165f4e-09bf-a445-a664-5e8edb9867b8
>      >>> Ancestors: ShoutCore-ul.68
>      >>>
>      >>> Fix bug in SHParserST80: Wrong styling after blocks with
> arguments without statements
>      >>
>      >> If you mean that Shout should accept [ :x ], then no, I'm pretty
> sure that's not valid smalltalk syntax, even if Parser accepts it.
>      >> The vertical bar, even though I consider it unnecessary in all
> cases, is mandatory when there are arguments.
>      >
>      > I only got to know this "shortcut syntax" because eliot used it
> either Cog or somewhere in trunk when preparing something (Spur? full block
> closures? I forgot). So this is a syntax idiosyncrasy that is in active
> use, not only "old code".
>      >
>      > Either we forbid it in the parser and change all of the image or
> allow it in Shout.
>
>      Can you give me examples?
>      I suspect those are just typos, which the parser accidentally accepted
>      (and Shout as well before my fixes).
>
>      Levente
> I don't remember seeing this syntax before and found it a bit surprising.
> So, for the sake of curiosity, I tried in some other dialects.
> [:x ] is accepted syntax in
> - Visualworks (8.3),
> - Pharo (v7 with OpalCompiler)
> - Smalltalk-80 (apple v0.?)
> [:x ] is invalid in
> - Dolphin
> - Smalltalk/X (jv branch)
> So it seems that it's something originating from original Smalltalk-80,
> but not reproducted in non derivated dialects...
> The bar is mandatory in blue book specification (see the last pages)
> Capture d’écran 2019-08-18 à 17.11.53.png
> So it seems that implementation did not agree with specifications for
> ages...
> Capture d’écran 2019-08-18 à 18.56.05.png
>
>      >
>      > Best regards
>      >       -Tobias
>      >
>      >>
>      >> Levente
>      >>
>      >>>
>      >>> Thanks Jakob for the report!
>      >>>
>      >>> =============== Diff against ShoutCore-ul.68 ===============
>      >>>
>      >>> Item was changed:
>      >>> ----- Method: SHParserST80>>parseBlockArguments (in category
> 'parse') -----
>      >>> parseBlockArguments
>      >>>
>      >>>     currentTokenFirst == $: ifFalse: [ ^self ].
>      >>>     [ currentTokenFirst == $: ] whileTrue: [
>      >>>             self
>      >>>                     scanPast: #blockArgColon;
>      >>>                     parseArgument: #blockPatternArg ].
>      >>> +   ((self parseVerticalBarForTemporaries: #blockArgsBar) and: [
>      >>> +           currentTokenFirst ~= $] ])
>      >>> +                   ifFalse: [
>      >>> +                           self fail ": Missing block args bar"
> ]!
>      >>> -   (self parseVerticalBarForTemporaries: #blockArgsBar) ifFalse:
> [
>      >>> -           self fail ": Missing block args bar" ]!
>      >>
>
>
>
>
>
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