[lojban] Re: Computer grammar question: non-left recursive RPN?

[GREGORY DYKE <lojban-out@lojban.org>]

As per promise, first a piece of code to illustrate how to make the tree from the new grammar.


    /** SumExpression  = Term
     *                 | SumExpression SumOp Term
     */

    ->LL(1)
    SumExpression = Term {SumOp Term}

Doing this recursively would not be good, which is why we are doing it iteratively

-------------------------------------
    private Tree sumExpression() {
        Tree t;

        t = term();
        while(token == PLUS || token == MINUS){
            int operator = sumOp();
            Tree right = term();
            t = new Tree.Binop(start, 
                               operator, t, 
                               right);
        }
        return t;
    }
-------------------------------------

> The ABNF form of this rule is:
> 
> rp-expression = rp-operand rp-operand operator
> 
> rp-operand = operand / rp-expression

just one thing, can an rp-expression be just an operand? I would have thought so...

Hey, wait! you need a stack to make the tree of rp-notation. You can't do it in one-token lookahead (I presume the point of this was to make it LL1)...

(take all this with a pinch of salt: I love this stuff and will gladly look into it further, but my memory is rather poor in these matters...)

Greg