[FWP] RecDescent, perhaps? math expression parsing

[Jeff Pinyan <jeffp@crusoe.net>]

I've been working on a mathematical expression parser off and on for a
year or so -- the goal is to make a module to break an expression down
into nodes, and (among other things) take the derivative.

I don't know yet what tool I'll be using to lex the expression.  I run
into much doodoo because of the following (abbreviated) problem:

  # OPEN = (
  # CLOSE = )
  # OP_H = ^
  # OP_M = [*/]
  # OP_L = [+-]
  # other names should be self-explanatory

  # ex: $expr is "3x^2"

  TERM ::=
    OPEN TERM CLOSE |
    FUNC OPEN TERM CLOSE |
    TERM OP_H TERM |
    NUM TERM |
    CONST TERM |
    VAR TERM |
    TERM OP_M TERM |
    TERM OP_L TERM |
    NUM |
    CONST |
    VAR

As you might be able to see, "3x^2" would match at TERM OP_H
TERM.  However, the first TERM in 'TERM OP_H TERM' matches at TERM OP_H
TERM again.  A lot of ugly recursion.  Blegh.

How do I get around this nasty recursion?  I'm at a bit of a loss.

-- 
Jeff "japhy" Pinyan     japhy@pobox.com     http://www.pobox.com/~japhy/
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