Added the sleep predicate

src/prolog/clause_types.rs

@@ -251,6 +251,7 @@ pub enum SystemClauseType {
     SetDoubleQuotes,
     SetSeed,
     SkipMaxList,
+    Sleep,
     Succeed,
     TermVariables,
     TruncateLiftedHeapTo,
@@ -402,6 +403,7 @@ impl SystemClauseType {
             &SystemClauseType::SetCutPointByDefault(_) => clause_name!("$set_cp_by_default"),
             &SystemClauseType::SetDoubleQuotes => clause_name!("$set_double_quotes"),
             &SystemClauseType::SkipMaxList => clause_name!("$skip_max_list"),
+            &SystemClauseType::Sleep => clause_name!("$sleep"),
             &SystemClauseType::Succeed => clause_name!("$succeed"),
             &SystemClauseType::TermVariables => clause_name!("$term_variables"),
             &SystemClauseType::TruncateLiftedHeapTo => clause_name!("$truncate_lh_to"),
@@ -525,6 +527,7 @@ impl SystemClauseType {
             ("$set_double_quotes", 1) => Some(SystemClauseType::SetDoubleQuotes),
             ("$set_seed", 1) => Some(SystemClauseType::SetSeed),
             ("$skip_max_list", 4) => Some(SystemClauseType::SkipMaxList),
+            ("$sleep", 1) => Some(SystemClauseType::Sleep),
             ("$store_global_var", 2) => Some(SystemClauseType::StoreGlobalVar),
             ("$store_global_var_with_offset", 2) => Some(SystemClauseType::StoreGlobalVarWithOffset),
             ("$term_variables", 2) => Some(SystemClauseType::TermVariables),

src/prolog/lib/time.pl

@@ -9,11 +9,15 @@
    '$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),
+    '$sleep'(T).
+
 time(Goal) :-
         '$cpu_now'(T0),
         Goal,

src/prolog/machine/system_calls.rs

@@ -3092,6 +3092,22 @@ impl MachineState {
                 if let Err(err) = self.skip_max_list() {
                     return Err(err);
                 },
+            &SystemClauseType::Sleep => {
+                let time = self.store(self.deref(self[temp_v!(1)]));
+
+                let time = match Number::try_from((time, &self.heap)) {
+                    Ok(Number::Float(OrderedFloat(n))) => n,
+                    Ok(Number::Fixnum(n)) => n as f64,
+                    Ok(Number::Integer(n)) => n.to_f64(),
+                    _ => {
+                        unreachable!()
+                    }
+                };
+
+                let duration = Duration::new(1, 0);
+                let duration = duration.mul_f64(time);
+                ::std::thread::sleep(duration);
+            }
             &SystemClauseType::StoreGlobalVar => {
                 let key = self[temp_v!(1)];