package mb.nabl2.solver.solvers;

import org.metaborg.util.functions.PartialFunction2;

import mb.nabl2.terms.ITerm;

@FunctionalInterface
public interface CallExternal extends PartialFunction2<String, Iterable<? extends ITerm>, ITerm> {

}
@@ -111,16 +111,44 @@
 ITerm;%0A%0A
+import java.util.Optional;%0A%0A
 @Functio
@@ -259,10 +259,94 @@
 Term%3E %7B%0A
+    static CallExternal never() %7B%0A        return (t1, t2) -%3E Optional.empty();%0A    %7D
 %0A%7D

Add never() static method to CallExternal