Merge pull request #371 from notoria/sleep

Added the sleep predicate

src/prolog/lib/time.pl

@@ -3,17 +3,26 @@
    Part of Scryer Prolog.
 
    This library provides predicates for reasoning about time.
-   sleep/1 should be implemented here, sleeping for a number of seconds.
-   In addition, this library should provide reasoning about time stamps.
+   Reasoning about time stamps would be a useful addition, for example
+   by obtaining the current time, comparing and formatting it.
 
    '$cpu_new' can be replaced by statistics/2 once that is implemented.
 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
 
-:- module(time, [time/1]).
+:- module(time, [sleep/1, time/1]).
 
 :- use_module(library(format)).
 :- use_module(library(iso_ext)).
 
+sleep(T) :-
+    builtins:must_be_number(T, sleep),
+    (   T < 0 ->
+        throw(domain_error(not_less_than_zero, T))
+    ;   T > 0xfffffffffffffbff ->
+        throw(domain_error(not_great_than_0xfffffffffffffbff, T))
+    ;   '$sleep'(T)
+    ).
+
 time(Goal) :-
         '$cpu_now'(T0),
         setup_call_cleanup(true,