ADDED: library(time), providing time/1 for benchmarking

sleep/1 and predicates for reasoning about time stamps should also
be added to this library.

src/prolog/lib/time.pl

@@ -0,0 +1,51 @@
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   Written April 2020 by Markus Triska (triska@metalevel.at)
+   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.
+
+   '$cpu_new' can be replaced by statistics/2 once that is implemented.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+:- module(time, [time/1]).
+
+:- use_module(library(format)).
+:- use_module(library(iso_ext)).
+
+time(Goal) :-
+        '$cpu_now'(T0),
+        Goal,
+        '$cpu_now'(T),
+        Time is T - T0,
+        (   bb_get('$first_answer', true) ->
+            format("   % CPU time: ~3f seconds~n", [Time])
+        ;   format("% CPU time: ~3f seconds~n   ", [Time])
+        ).
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+?- time((true;false)).
+   % CPU time: 0.000 seconds
+   true
+;  false.
+
+:- time(use_module(library(clpz))).
+   % CPU time: 2.762 seconds
+   true
+;  false.
+
+:- time(use_module(library(lists))).
+   % CPU time: 0.000 seconds
+   true
+;  false.
+
+?- time(member(X, [a,b,c])).
+   % CPU time: 0.000 seconds
+   X = a
+;  % CPU time: 0.002 seconds
+   X = b
+;  % CPU time: 0.004 seconds
+   X = c
+;  false.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */