[m-rev.] Re: [m-dev.] Commas considered optional

[Fergus Henderson]

On 29-Nov-2001, Ralph Becket <rafe at cs.mu.OZ.AU> wrote:
> A common topic for debate is how to improve the syntax of Mercury.
> Possibly for the first time ever in the history of such discussions, we
> suggest taking something out: the commas.
> 
> We've just conducted an experiment on the parser making the use of
> commas optional, interpreting simple juxtaposition as indicating an
> implicit intervening comma.  We've used this change to successfully
> compile some test programs (including non-trivial programs such as
> samples/calculator.m) written without commas.

FWIW, here's the diff.  This passes bootcheck.

Estimated hours taken: 1

library/parser.m:
	Treat term juxtaposition as equivalent to ",".

Workspace: /home/earth/fjh/ws-earth4/mercury
Index: library/parser.m
===================================================================
RCS file: /home/mercury1/repository/mercury/library/parser.m,v
retrieving revision 1.38
diff -u -d -r1.38 parser.m
--- library/parser.m	8 Nov 2001 15:30:38 -0000	1.38
+++ library/parser.m	29 Nov 2001 04:15:03 -0000
@@ -480,6 +480,31 @@
 			TermContext) },
 		parser__parse_rest(MaxPriority, IsArg, OpPriority, OpTerm, Term)
 	;
+		% juxtaposition -- treat like ","
+		{ IsArg = no },
+		{ Op = "," },
+		parser__get_ops_table(OpTable),
+		{ ops__lookup_infix_op(OpTable, Op,
+				OpPriority, LeftAssoc, RightAssoc) },
+		{ OpPriority =< MaxPriority },
+		{ parser__check_priority(LeftAssoc, OpPriority, LeftPriority) },
+		{ parser__adjust_priority(RightAssoc, OpPriority,
+					RightPriority) },
+		parser__parse_term_2(RightPriority, IsArg, RightTerm0),
+		{ RightTerm0 = ok(RightTerm) }
+	->
+		{ LeftTerm = term__functor(_, _, LeftContext) ->
+			TermContext = LeftContext
+		; RightTerm = term__functor(_, _, RightContext) ->
+			TermContext = RightContext
+		;
+			term__context_init(TermContext)
+		},
+		{ OpTerm = term__functor(term__atom(Op),
+				[LeftTerm, RightTerm], TermContext) },
+		parser__parse_rest(MaxPriority, IsArg, OpPriority,
+			OpTerm, Term)
+	;
 		{ Term = ok(LeftTerm) }
 	).
 
@@ -705,6 +730,15 @@
 		    { List = ok(term__functor(term__atom("[|]"), [Arg, Tail],
 				TermContext)) }
 		;
+		    % check for arguments juxtaposed without any intervening
+		    % comma
+		    parser__unget_token(Token, Context),
+		    parser__parse_list(Tail0),
+		    { Tail0 = ok(Tail) }
+		->
+		    { List = ok(term__functor(term__atom("[|]"),
+					[Arg, Tail], TermContext)) }
+		;
 		    parser__unexpected_tok(Token, Context,
 			"expected comma, `|', `]', or operator", List)
 		)
@@ -736,6 +770,14 @@
 		    )
 		; { Token = close } ->
 		    { List = ok([Arg]) }
+		;
+		    % check for arguments juxtaposed without any intervening
+		    % comma
+		    parser__unget_token(Token, Context),
+		    parser__parse_args(Tail0),
+		    { Tail0 = ok(Tail) }
+		->
+		    { List = ok([Arg|Tail]) }
 		;
 		    parser__unexpected_tok(Token, Context,
 				"expected `,', `)', or operator", List)

-- 
Fergus Henderson <fjh at cs.mu.oz.au>  |  "I have always known that the pursuit
The University of Melbourne         |  of excellence is a lethal habit"
WWW: <http://www.cs.mu.oz.au/~fjh>  |     -- the last words of T. S. Garp.
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