From: Lui Kore <usurffx@...>
Date: 2010-02-15T17:17:15+09:00
Subject: [ann] rsec - parsec for ruby1.9

Hi dear everyone,

I just made a small parser combinator library for ruby1.9 (sadly it's
1.9 only).
It's simple(buggy) and fast(ha, it beats treetop on arithmetics!).
Please have a look if you are interested in.

install:
gem install rsec -s http://gemcutter.org

source code (about 500 LOCs):
http://github.com/luikore/rsec

the terrible document:
http://wiki.github.com/luikore/rsec/

Yours, sincerely, and many best regards.

Helloworld: a simple arithmetic calculator
#---------------------------------------------------------

require 'rubygems'
require 'rsec'
include Rsec::Helpers

def arithmetic
  calculate = proc do |(p, *ps)|
    ps.each_slice(2).inject(p) do |left, (op, right)|
      left.send op.strip, right
    end
  end

  num    = /[+-]?[1-9]\d*(\.\d+)?/.r.map &:to_f
  bra    = '('.r.skip
  ket    = ')'.r.skip
  paren  = (bra << lazy{@expr} << ket).map &:first
  factor = paren | num
  term   = factor.join(/\s*[\*\/]\s*/).map &calculate
  @expr  = term.join(/\s*[\+\-]\s*/).map &calculate
end

puts arithmetic.parse '1 + 2.3 / 4 - 5 + 6 * 7.8 / (9 +10)'
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