Changeset 4488 for trunk/library

Timestamp:

10/05/08 14:08:31 (3 months ago)

Author:

pmoura

Message:

Added predicates plus/3 and succ/2 to the library object "integer".

Files:

• trunk/library/integer.lgt (modified) (3 diffs)

trunk/library/integer.lgt

@@ -4 +4 @@
 
     :- info([
-        version is 1.1,
+        version is 1.2,
         author is 'Paulo Moura',
-        date is 2007/4/20,
+        date is 2008/10/5,
         comment is 'Integer data type predicates.']).
 
@@ -15 +15 @@
         comment is 'Returns integers in the interval defined by the two first arguments.',
         argnames is ['Lower', 'Upper', 'Integer']]).
+
+    :- public(plus/3).
+    :- mode(plus(+integer, +integer, ?integer), zero_or_one).
+    :- mode(plus(+integer, ?integer, +integer), zero_or_one).
+    :- mode(plus(?integer, +integer, +integer), zero_or_one).
+    :- info(plus/3, [
+        comment is 'Reversible integer sum. At least two of the arguments must be instantiated to integers.',
+        argnames is ['I', 'J', 'Sum']]).
+
+    :- public(succ/2).
+    :- mode(succ(+integer, ?integer), zero_or_one).
+    :- mode(succ(?integer, +integer), zero_or_one).
+    :- info(plus/2, [
+        comment is 'Successor of a natural number. At least one of the arguments must be instantiated to a natural number.',
+        argnames is ['I', 'J']]).
 
     between(Lower, Upper, Integer) :-
@@ -33 +48 @@
         generate(Next, Upper, Integer).
 
+    plus(I, J, Sum) :-
+        integer(I),
+        integer(J), !,
+        Sum is I + J.
+    plus(I, J, Sum) :-
+        integer(I),
+        integer(Sum), !,
+        J is Sum - I.
+    plus(I, J, Sum) :-
+        integer(J),
+        integer(Sum), !,
+        I is Sum - J.
+
+    succ(I, J) :-
+        integer(I), !,
+        I >= 0,
+        J is I + 1.
+    succ(I, J) :-
+        integer(J),
+        (   J =:= 0 ->
+            fail
+        ;   J > 0,
+            I is J - 1
+        ).
+
     valid(Integer) :-
         integer(Integer).