throw exception when predicate not found

src/prolog/machine/machine_state.rs

@@ -210,11 +210,11 @@ pub struct MachineState {
 
 pub(crate) type CallResult = Result<(), Vec<HeapCellValue>>;
 
-fn predicate_existence_error(name: ClauseName, arity: usize) -> Vec<HeapCellValue>
+fn predicate_existence_error(name: ClauseName, arity: usize, h: usize) -> Vec<HeapCellValue>
 {
     let name = HeapCellValue::Addr(Addr::Con(Constant::Atom(name)));
 
-    let mut error = functor!("existence_error", 2, [heap_atom!("procedure"), heap_str!(4)]);
+    let mut error = functor!("existence_error", 2, [heap_atom!("procedure"), heap_str!(3 + h)]);
     error.append(&mut functor!("/", 2, [name, heap_integer!(arity)], Fixity::In));
 
     error
@@ -238,7 +238,7 @@ pub(crate) trait CallPolicy: Any {
     {
         match idx.0.get() {
             IndexPtr::Undefined =>
-                return Err(predicate_existence_error(name, arity)),
+                return Err(predicate_existence_error(name, arity, machine_st.heap.h)),
             IndexPtr::Index(compiled_tl_index) => {
                 let module_name = idx.1;
 
@@ -258,7 +258,7 @@ pub(crate) trait CallPolicy: Any {
     {
         match idx.0.get() {
             IndexPtr::Undefined =>
-                return Err(predicate_existence_error(name, arity)),
+                return Err(predicate_existence_error(name, arity, machine_st.heap.h)),
             IndexPtr::Index(compiled_tl_index) => {
                 let module_name = idx.1;
 

src/prolog/machine/machine_state_impl.rs

@@ -925,6 +925,13 @@ impl MachineState {
         self.p  = CodePtr::DirEntry(59, clause_name!("builtin"));
     }
 
+    fn unwind_stack(&mut self) {
+        self.b = self.block;
+        self.or_stack.truncate(self.b);
+        
+        self.fail = true;
+    }  
+
     fn throw_exception(&mut self, hcv: Vec<HeapCellValue>) {
         let h = self.heap.h;
 
@@ -1535,12 +1542,8 @@ impl MachineState {
                 let addr = self.deref(self[temp_v!(1)].clone());
                 self.reset_block(addr);
             },
-            &BuiltInInstruction::UnwindStack => {
-                self.b = self.block;
-                self.or_stack.truncate(self.b);
-
-                self.fail = true;
-            },
+            &BuiltInInstruction::UnwindStack =>
+                self.unwind_stack(),
             &BuiltInInstruction::InternalCallN =>
                 self.handle_internal_call_n(call_policy, code_dirs),
             &BuiltInInstruction::Fail => {