Merge pull request #972 from pmoura/add_pid_predicate

Add pid/1 predicate to the os library

src/lib/os.pl

@@ -14,7 +14,8 @@
 
 :- module(os, [getenv/2,
                setenv/2,
-               unsetenv/1]).
+               unsetenv/1,
+               pid/1]).
 
 :- use_module(library(error)).
 :- use_module(library(charsio)).
@@ -33,6 +34,10 @@ unsetenv(Key) :-
         must_be_env_var(Key),
         '$unsetenv'(Key).
 
+pid(PID) :-
+        can_be(integer, PID),
+        '$pid'(PID).	
+
 /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    For now, we only support a restricted subset of variable names.