/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
   Written April 2020 by Markus Triska (triska@metalevel.at)
   Part of Scryer Prolog.

   This library provides predicates for reasoning about time.
   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.
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:- 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) :-
        '$cpu_now'(T0),
        Goal,
        '$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.
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