correct keysort type error (re: #34)

src/prolog/machine/machine_errors.rs

@@ -37,24 +37,12 @@ impl MachineState {
         }
     }
 
-    // see 8.4.4 of Draft Technical Corrigendum 2.
+    fn check_for_list_pairs(&self, list: Addr) -> Result<(), MachineError> {
-    pub(super) fn check_keysort_errors(&self) -> Result<(), MachineError> {
+        match self.detect_cycles(usize::max_value(), list.clone()) {
-        let pairs  = self.store(self.deref(self[temp_v!(1)].clone()));
+            CycleSearchResult::NotList if !list.is_ref() =>
-        let sorted = self.store(self.deref(self[temp_v!(2)].clone()));
+                Err(self.error_form(self.type_error(ValidType::List, list))),
-
-        match self.detect_cycles(usize::max_value(), pairs.clone()) {
-            CycleSearchResult::PartialList(..) =>
-                Err(self.error_form(self.instantiation_error())),
-            CycleSearchResult::NotList =>
-                Err(self.error_form(self.type_error(ValidType::List, pairs))),
-            _ => Ok(())
-        }?;
-
-        match self.detect_cycles(usize::max_value(), sorted.clone()) {
-            CycleSearchResult::NotList if !sorted.is_ref() =>
-                Err(self.error_form(self.type_error(ValidType::List, sorted))),
             _ => {
-                let mut addr = sorted;
+                let mut addr = list;
 
                 while let Addr::Lis(l) = self.store(self.deref(addr)) {
                     let mut new_l = l;
@@ -79,6 +67,22 @@ impl MachineState {
         }
     }
 
+    // see 8.4.4 of Draft Technical Corrigendum 2.
+    pub(super) fn check_keysort_errors(&self) -> Result<(), MachineError> {
+        let pairs  = self.store(self.deref(self[temp_v!(1)].clone()));
+        let sorted = self.store(self.deref(self[temp_v!(2)].clone()));
+
+        match self.detect_cycles(usize::max_value(), pairs.clone()) {
+            CycleSearchResult::PartialList(..) =>
+                Err(self.error_form(self.instantiation_error())),
+            CycleSearchResult::NotList =>
+                Err(self.error_form(self.type_error(ValidType::List, pairs))),
+            _ => Ok(())
+        }?;
+
+        self.check_for_list_pairs(sorted)
+    }
+
     pub(super) fn evaluation_error(&self, eval_error: EvalError) -> MachineError {
         functor!("evaluation_error", 1, [heap_atom!(eval_error.as_str())])
     }

src/prolog/machine/machine_state_impl.rs

@@ -1742,7 +1742,7 @@ impl MachineState {
                     _ => Err(self.error_form(self.type_error(ValidType::Pair,
                                                              self.heap[s].as_addr(s))))
                 },
-            a => Err(self.error_form(self.type_error(ValidType::Callable, a)))
+            a => Err(self.error_form(self.type_error(ValidType::Pair, a)))
         }
     }