reset attributed variable state between toplevel queries (#242)

src/prolog/clause_types.rs

@@ -179,6 +179,7 @@ pub enum SystemClauseType {
     FetchGlobalVar,
     FetchGlobalVarWithOffset,
     GetChar,
+    ResetAttrVarState,
     TruncateIfNoLiftedHeapGrowthDiff,
     TruncateIfNoLiftedHeapGrowth,
     GetAttributedVariableList,
@@ -289,6 +290,7 @@ impl SystemClauseType {
                 clause_name!("$fetch_global_var_with_offset")
             }
             &SystemClauseType::GetChar => clause_name!("$get_char"),
+            &SystemClauseType::ResetAttrVarState => clause_name!("$reset_attr_var_state"),
             &SystemClauseType::TruncateIfNoLiftedHeapGrowth => {
                 clause_name!("$truncate_if_no_lh_growth")
             }
@@ -408,6 +410,7 @@ impl SystemClauseType {
             ("$fetch_global_var", 2) => Some(SystemClauseType::FetchGlobalVar),
             ("$fetch_global_var_with_offset", 3) => Some(SystemClauseType::FetchGlobalVarWithOffset),
             ("$get_char", 1) => Some(SystemClauseType::GetChar),
+            ("$reset_attr_var_state", 0) => Some(SystemClauseType::ResetAttrVarState),
             ("$truncate_if_no_lh_growth", 1) => {
                 Some(SystemClauseType::TruncateIfNoLiftedHeapGrowth)
             }

src/prolog/machine/attributed_variables.rs

@@ -32,9 +32,9 @@ impl AttrVarInitializer {
 
     #[inline]
     pub(super) fn reset(&mut self) {
+	self.attribute_goals.clear();
         self.attr_var_queue.clear();
         self.bindings.clear();
-	self.attribute_goals.clear();
     }
 }
 

src/prolog/machine/system_calls.rs

@@ -1680,6 +1680,9 @@ impl MachineState {
                     }
                 };
             },
+            &SystemClauseType::ResetAttrVarState => {
+                self.attr_var_init.reset();
+            }
             &SystemClauseType::RemoveCallPolicyCheck => {
                 let restore_default = match call_policy.downcast_mut::<CWILCallPolicy>().ok() {
                     Some(call_policy) => {

src/prolog/toplevel.pl

@@ -44,7 +44,8 @@
     ),
     (  '$get_b_value'(B), call(Term), '$write_eqs_and_read_input'(B, VarList), !
     ;  write('false.'), nl
-    ).
+    ),
+    '$reset_attr_var_state'.
 
 '$needs_bracketing'(Value, Op) :-
     catch((functor(Value, F, _),