ASTNeq.java

public class ASTNeq implements ASTNode {
    ASTNode lhs, rhs;

    public ASTNeq(ASTNode l, ASTNode r) {
        this.lhs = l;
        this.rhs = r;
    }

    @Override
    public IValue eval(Environment<IValue> e) throws InterpreterError {
        IValue v1 = lhs.eval(e);
        IValue v2 = rhs.eval(e);

        if (v1 instanceof VClosure || v2 instanceof VClosure) {
            throw new InterpreterError("illegal types to ~= operator");
        }

        return new VBool(!v1.equals(v2));
    }

    @Override
    public ASTType typecheck(Environment<ASTType> e) throws TypeCheckError, InterpreterError {
        ASTType l = lhs.typecheck(e);
        ASTType r = rhs.typecheck(e);
        
        if (l instanceof ASTTArrow || r instanceof ASTTArrow)
            throw new TypeCheckError("~=: cannot compare functions");
            
        if (l.subtypeOf(r, e) || r.subtypeOf(l, e)) {
            return ASTTBool.tbool;
        }
        
        throw new TypeCheckError("~=: incompatible types for comparison: " + l.toStr() + " and " + r.toStr());
    }

    @Override
    public boolean isFreeOutsideLambda(String id) {
        return lhs.isFreeOutsideLambda(id) || rhs.isFreeOutsideLambda(id);
    }

}