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The iso standard want's call(G) to throw a type_error(callable, G), when G contains parts that cannot be called, but it is
OK for parts of G to be variables, such as G=(write(hey), X).

--- a/builtins.c

+++ b/builtins.c

@@ -216,10 +216,29 @@

 }

 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;

 }