1 files changed, 20 insertions, 1 deletions
diff --git a/builtins.c b/builtins.c
index 9aee573..a037a23 100644
--- a/builtins.c
+++ b/builtins.c
@@ -216,10 +216,29 @@ builtinfail(Term *goal, Binding **bindings, Module *module)
 }
 
 int
+canbecalled(Term *t)
+{
+	if(t->tag == VariableTerm || t->tag == AtomTerm)
+		return 1;
+	if(t->tag != CompoundTerm)
+		return 0;
+
+	if(t->arity == 2 && (runestrcmp(t->text, L",") == 0 || runestrcmp(t->text, L";") == 0))
+		return canbecalled(t->children) && canbecalled(t->children->next);
+	else
+		return 1;
+}
+
+int
 builtincall(Term *goal, Binding **bindings, Module *module)
 {
 	USED(bindings);
-	goalstack = addgoals(goalstack, goal->children, module);
+	Term *callgoal = goal->children;
+
+	if(!canbecalled(callgoal))
+		Throw(typeerror(L"callable", callgoal));
+
+	goalstack = addgoals(goalstack, callgoal, module);
 	return 1;
 }