[m-dev.] for review: allow io__read for some univs

[Mark Anthony BROWN]

Hi,

This is a fairly simple change, but should be reviewed since
it will be visible in the documentation.

Cheers,
Mark.


Estimated hours taken: 0.5

Allow io__read, term__term_to_type, etc, to read in some values of
type univ.

library/io.m:
	Fix a misleading comment---some limitations of `io__read'
	were not explicit.

library/term.m:
	Add some extra cases to `term_to_univ_special_case', to
	handle values of type `univ' which contain either an
	int, a float or a string.

Index: library/io.m
===================================================================
RCS file: /home/mercury1/repository/mercury/library/io.m,v
retrieving revision 1.186
diff -u -r1.186 io.m
--- io.m	1999/10/18 15:46:27	1.186
+++ io.m	1999/10/20 06:29:47
@@ -281,10 +281,12 @@
 %		For higher-order types, or for types defined using the
 %		foreign language interface (pragma c_code), the text output
 %		will only describe the type that is being printed, not the
-%		value, and the result may not be parsable by io__read.
-%		But in all other cases the format used is standard Mercury
-%		syntax, and if you do append a period and newline (".\n"),
-%		then the results can be read in again using `io__read'.
+%		value, and the result may not be parsable by `io__read'.
+%		For the types `univ' and `typeinfo', the result may not
+%		be parsable by `io__read', either.  But in all other cases
+%		the format used is standard Mercury syntax, and if you do
+%		append a period and newline (".\n"), then the results can
+%		be read in again using `io__read'.
 
 :- pred io__nl(io__state, io__state).
 :- mode io__nl(di, uo) is det.
Index: library/term.m
===================================================================
RCS file: /home/mercury1/repository/mercury/library/term.m,v
retrieving revision 1.90
diff -u -r1.90 term.m
--- term.m	1999/10/18 11:13:42	1.90
+++ term.m	1999/10/20 04:08:57
@@ -472,12 +472,30 @@
 term__term_to_univ_special_case("builtin", "c_pointer", _, _, _, 
 		_, _) :-
 	fail.
-term__term_to_univ_special_case("std_util", "univ", _, _, _, _, _) :-
+term__term_to_univ_special_case("std_util", "univ", [], Term, _, _, Result) :-
 	% Implementing this properly would require keeping a
 	% global table mapping from type names to type_infos
 	% for all of the types in the program...
-	% so for the moment, we don't allow it.
-	fail.
+	% so for the moment, we only allow it for basic types.
+	Term = term__functor(term__atom("univ"), [Arg], _),
+	Arg = term__functor(term__atom(":"), [Value, Type], _),
+	(
+		Type = term__functor(term__atom("int"), [], _),
+		Value = term__functor(term__integer(Int), [], _),
+		Univ = univ(Int)
+	;
+		Type = term__functor(term__atom("string"), [], _),
+		Value = term__functor(term__string(String), [], _),
+		Univ = univ(String)
+	;
+		Type = term__functor(term__atom("float"), [], _),
+		Value = term__functor(term__float(Float), [], _),
+		Univ = univ(Float)
+	),
+	% The result is a `univ', but it is also wrapped in a `univ'
+	% like all the other results returned from this procedure.
+	Result = ok(univ(Univ)).
+
 term__term_to_univ_special_case("std_util", "type_info", _, _, _, _, _) :-
 	% ditto
 	fail.

-- 
Mark Brown, PhD student            )O+  |  "Another of Fortran's breakthroughs
(m.brown at cs.mu.oz.au)                   |  was the GOTO statement, which was...
Dept. of Computer Science and Software  |  uniquely simple and understandable"
Engineering, University of Melbourne    |              -- IEEE, 1994
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