public static IList compose(IList rel1, IList rel2) {
Type otherTupleType = rel2.getType().getFieldTypes();
if (rel1.getElementType() == voidType) return rel1;
if (otherTupleType == voidType) return rel2;
if (rel1.getElementType().getArity() != 2 || otherTupleType.getArity() != 2)
throw new IllegalOperationException("compose", rel1.getElementType(), otherTupleType);
// Relaxed type constraint:
if (!rel1.getElementType().getFieldType(1).comparable(otherTupleType.getFieldType(0)))
throw new IllegalOperationException("compose", rel1.getElementType(), otherTupleType);
Type[] newTupleFieldTypes =
new Type[] {rel1.getElementType().getFieldType(0), otherTupleType.getFieldType(1)};
Type tupleType = typeFactory.tupleType(newTupleFieldTypes);
IListWriter w = new ListWriter(tupleType);
for (IValue v1 : rel1) {
ITuple tuple1 = (ITuple) v1;
for (IValue t2 : rel2) {
ITuple tuple2 = (ITuple) t2;
if (tuple1.get(1).isEqual(tuple2.get(0))) {
w.append(Tuple.newTuple(tuple1.get(0), tuple2.get(1)));
}
}
}
return w.done();
}
public static int arity(IList rel) {
return rel.getElementType().getArity();
}
