[Pyparsing] Operator Precedence and Associativity.

[Ralph C. <ra...@in...>]

Hi,

PyParsing seems great;  many thanks.

But I'm having trouble concocting the right grammar for the typical
binary operator part.  I'm aware of the latest fourFn.py but its use of
ZeroOrMore() results in

                         +
    1 + 2 + 3    ==>    /|\
                       1 2 3

whereas I'd like the left associativity explicit, i.e.

                         +
                        / \
    1 + 2 + 3    ==>   +   3
                      / \
                     1   2

I can achieve this with a right-associative operator, e.g. exponent, but
how do I do this for left-associative ones whilst avoiding endless
left-recursion?

I wonder if PyParsing would benefit from being able to define operator
tables, similar to K&R's, giving the tokens, precedence, and
associativity, and being able to plumb that into the rest of the
recursive descent parser at some point?

Cheers,


Ralph.