ASTIf.java

public class ASTIf implements ASTNode {
    ASTNode cond, ifBranch, elseBranch;

    public ASTIf(ASTNode cond, ASTNode ifBranch, ASTNode elseBranch) {
        this.cond = cond;
        this.ifBranch = ifBranch;
        this.elseBranch = elseBranch;
    }

    @Override
    public IValue eval(Environment<IValue> e) throws InterpreterError {
        IValue condVal = cond.eval(e);
        if (!(condVal instanceof VBool)) {
            throw new InterpreterError("condition of if must be a boolean");
        }

        if (((VBool) condVal).getval()) {
            return ifBranch.eval(e);
        } else {
            return elseBranch.eval(e);
        }
    }

    @Override
    public ASTType typecheck(Environment<ASTType> e) throws TypeCheckError, InterpreterError {
        ASTType condType = cond.typecheck(e);
        if (!(condType instanceof ASTTBool)) {
            throw new TypeCheckError("if: condition not bool, got " + condType.toStr());
        }

        ASTType thenType = ifBranch.typecheck(e);
        ASTType elseType = elseBranch.typecheck(e);

        try {
            return thenType.computeLUB(elseType, e);
        } catch (TypeCheckError tce) {
            throw new TypeCheckError("if: branches have incompatible types: " + thenType.toStr() + " vs " + elseType.toStr());
        }
    }

    @Override
    public boolean isFreeOutsideLambda(String id) {
        return cond.isFreeOutsideLambda(id) || ifBranch.isFreeOutsideLambda(id) || elseBranch.isFreeOutsideLambda(id);
    }

}