ASTSub.java

public class ASTSub implements ASTNode {

    ASTNode lhs, rhs;

	public ASTSub(ASTNode l, ASTNode r) {
		lhs = l;
		rhs = r;
    }

	@Override
    public IValue eval(Environment<IValue> e) throws InterpreterError {
		IValue v1 = lhs.eval(e);
		IValue v2 = rhs.eval(e);
		if (v1 instanceof VInt && v2 instanceof VInt) {
			return new VInt(((VInt) v1).getval() - ((VInt) v2).getval());
		} else {
			throw new InterpreterError("illegal types to + operator");
		}
    }

	@Override
	public ASTType typecheck(Environment<ASTType> e) throws TypeCheckError, InterpreterError {
		ASTType l = lhs.typecheck(e);
    	ASTType r = rhs.typecheck(e);
		if (!(l instanceof ASTTInt) || !(r instanceof ASTTInt))
			throw new TypeCheckError("-: arg types not int");
		return ASTTInt.tint;
	}
	
	@Override
	public boolean isFreeOutsideLambda(String id) {
		return lhs.isFreeOutsideLambda(id) || rhs.isFreeOutsideLambda(id);
	}

}