[m-rev.] for review: change list constructor from `./2' to `[|]/2'

[Simon Taylor]

On 24-Sep-2001, Fergus Henderson <fjh at cs.mu.OZ.AU> wrote:
> On 23-Sep-2001, Simon Taylor <stayl at cs.mu.OZ.AU> wrote:
> > Change the list constructor from `./2' to `[|]/2'. `./2' will
> > eventually become the module qualification operator.
> 
> Are there any bootstrapping issues with this change?

Once this change is installed, people will need to rebuild interface
files that refer to `./2'  e.g. library/list.int. This will break
installation of the source distribution in some cases (when C files
need to be updated) so I'll need to update the check in configure.in
once this change has been installed everywhere.
 
> > +++ NEWS	2001/09/23 03:44:04
> > @@ -22,6 +22,11 @@
> >    Reference Manual.
> >  
> >  Changes to the Mercury standard library:
> > +* The constructor for lists is now called '[|]' rather than '.'.
> > +  `./2' will eventually become the module qualification operator.
> > +  This change only affects programs which use `./2' explicitly.
> > +  Programs which only use the `[H | T]' syntax will be unaffected.
> 
> This is a change to the language rather than to the standard library.

It's actually a change to both. For example, the behaviour of
parser__read_term has changed.

> > Index: doc/reference_manual.texi
> > ===================================================================
> > -However, the meaning of some terms in Mercury is different to that
> > -in Prolog.  @xref{Data-terms}.
> > +Also, the constructor for list terms in Mercury is @code{[|]/2}, not
> > + at code{./2} as in Prolog.  The meaning of some terms in Mercury is
> > +different to that in Prolog.  @xref{Data-terms}.
> 
> I think it would be better to split the last sentence into a new
> paragraph:
> 
> 	Note, however, that the meaning of some terms ...

Done.
 
> > +The following terms are all equivalent:
> > + at example
> > +[1, 2, 3]
> > +[1, 2 | [3]]
> > +[1 | [2, 3]]
> > +'[|]'(1, '[|]'(2, '[|]'(3, [])))
> > + at end example
> 
> I suggest also including
> 
> 	[1, 2, 3 | []]
> 
> in that list of examples.

Done. 

> > Index: tests/debugger/declarative/app.exp
> > ===================================================================
> > RCS file: /home/mercury1/repository/tests/debugger/declarative/app.exp,v
> > retrieving revision 1.10
> > diff -u -u -r1.10 app.exp
> > --- tests/debugger/declarative/app.exp	2000/10/01 03:13:42	1.10
> > +++ tests/debugger/declarative/app.exp	2001/09/23 07:34:37
> > @@ -15,7 +15,10 @@
> >  mdb> finish -n
> >        16:      5  5 EXIT pred app:app/3-0 (det) app.m:26 (app.m:28)
> >  mdb> dd
> > -app([4, 5], [6, 7, 8], [4, 5, 6, 7, 8])
> > +pred app
> > +	[4, 5]
> > +	[6, 7, 8]
> > +	[4, 5, 6, 7, 8]
> 
> That change appears to be unrelated.

It's not. `browser/declarative_user__check_decl_atom_size' uses
a fairly crude heuristic to determine whether an atom will fit
on a line. Now that the list constructor is three characters long
rather than one, there are a few places in the tests which,
according to the heuristic, will no longer fit on one line.
I'm not sure whether it's worth special casing `[|]' in the
heuristic. I'll leave it as it is for now. Mark can decide
what he wants to do with it.

Simon.

--- NEWS	2001/09/24 05:47:50	1.4
+++ NEWS	2001/09/24 08:04:01
@@ -2,6 +2,11 @@
 ----------------------------------
 
 Changes to the Mercury language:
+* The constructor for lists is now called '[|]' rather than '.'.
+  `./2' will eventually become the module qualification operator.
+  This change only affects programs which use `./2' explicitly.
+  Programs which only use the `[H | T]' syntax will be unaffected.
+
 * We've extended the language to allow you to specify different clauses
   for different modes of a predicate or function.  This is done by
   putting mode annotations in the head of each clause.
@@ -22,10 +27,15 @@
   Reference Manual.
 
 Changes to the Mercury standard library:
-* The constructor for lists is now called '[|]' rather than '.'.
-  `./2' will eventually become the module qualification operator.
-  This change only affects programs which use `./2' explicitly.
-  Programs which only use the `[H | T]' syntax will be unaffected.
+* As mentioned above, the constructor for lists has changed from './2'
+  to `[|]/2'. This change affects the behaviour of the term manipulation
+  predicates in the standard library when dealing with values of
+  type `term__term/1' representing lists. The affected predicates are
+  parser__read_term, parser__read_term_from_string, term__type_to_term,
+  term__term_to_type, term_io__read_term and term_io__write_term.
+  Also beware that std_util__functor and std_util__deconstruct now
+  return `[|]' rather than `.' for lists, and calls to std_util__construct
+  which construct lists may need to be updated.
 
 * The predicates and functions in int.m, float, math.m and array.m now 
   generate exceptions rather than program aborts on domain errors and
--- reference_manual.texi	2001/09/24 05:49:23	1.2
+++ reference_manual.texi	2001/09/24 05:57:15
@@ -317,7 +317,9 @@
 as described below,
 and we support an extended set of builtin operators. @xref{Builtin Operators}.
 Also, the constructor for list terms in Mercury is @code{[|]/2}, not
- at code{./2} as in Prolog.  The meaning of some terms in Mercury is
+ at code{./2} as in Prolog.
+
+Note, however, that the meaning of some terms in Mercury is
 different to that in Prolog.  @xref{Data-terms}.
 
 A term is either a variable or a functor.
@@ -350,6 +352,7 @@
 The following terms are all equivalent:
 @example
 [1, 2, 3]
+[1, 2, 3 | []]
 [1, 2 | [3]]
 [1 | [2, 3]]
 '[|]'(1, '[|]'(2, '[|]'(3, [])))
Index: std_util.m
===================================================================
RCS file: /home/mercury1/repository/mercury/library/std_util.m,v
retrieving revision 1.240
diff -u -u -r1.240 std_util.m
--- std_util.m	2001/08/24 09:31:25	1.240
+++ std_util.m	2001/09/24 07:47:20
@@ -518,7 +518,7 @@
 	%
 	% 	- for user defined types, the functor that is given
 	% 	  in the type definition. For lists, this
-	% 	  means the functors ./2 and []/0 are used, even if
+	% 	  means the functors [|]/2 and []/0 are used, even if
 	% 	  the list uses the [....] shorthand.
 	%	- for integers, the string is a base 10 number,
 	%	  positive integers have no sign.
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