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/clause_types.rs

@@ -241,6 +241,7 @@ pub enum SystemClauseType {
     GetDoubleQuotes,
     InstallNewBlock,
     Maybe,
+    CPU_now,
     QuotedToken,
     ReadTermFromChars,
     ResetBlock,
@@ -347,6 +348,7 @@ impl SystemClauseType {
             &SystemClauseType::PartialStringTail => clause_name!("$partial_string_tail"),
             &SystemClauseType::LiftedHeapLength => clause_name!("$lh_length"),
             &SystemClauseType::Maybe => clause_name!("maybe"),
+            &SystemClauseType::CPU_now => clause_name!("$cpu_now"),
             &SystemClauseType::ModuleAssertDynamicPredicateToFront => {
                 clause_name!("$module_asserta")
             }
@@ -480,6 +482,7 @@ impl SystemClauseType {
             ("$install_inference_counter", 3) => Some(SystemClauseType::InstallInferenceCounter),
             ("$lh_length", 1) => Some(SystemClauseType::LiftedHeapLength),
             ("$maybe", 0) => Some(SystemClauseType::Maybe),
+            ("$cpu_now", 1) => Some(SystemClauseType::CPU_now),
             ("$module_exists", 1) => Some(SystemClauseType::ModuleExists),
             ("$module_of", 2) => Some(SystemClauseType::ModuleOf),
             ("$module_retract_clause", 5) => Some(SystemClauseType::ModuleRetractClause),

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.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

src/prolog/machine/system_calls.rs

@@ -28,6 +28,9 @@ use std::io::{stdout, Write};
 use std::iter::once;
 use std::rc::Rc;
 
+use std::time::Duration;
+use cpu_time::ProcessTime;
+
 use crate::crossterm::event::{read, Event, KeyCode, KeyEvent};
 use crate::crossterm::terminal::{enable_raw_mode, disable_raw_mode};
 
@@ -1952,6 +1955,13 @@ impl MachineState {
 
                 self.fail = result;
             }
+            &SystemClauseType::CPU_now => {
+                let a1 = self[temp_v!(1)];
+                let a2 = ProcessTime::now().as_duration().as_secs_f64();
+                let addr = self.heap.put_constant(Constant::Float(OrderedFloat(a2)));
+
+                self.unify(a1, addr);
+            }
             &SystemClauseType::OpDeclaration => {
                 let priority = self[temp_v!(1)];
                 let specifier = self[temp_v!(2)];