Make your own parser

New operators and functions are defined in terms of _parse and ctx. _parse is the internal counterpart to .parse. ctx is a Rsec::ParseContext instance, which is derived from StringScanner. Any methods of StringScanner is available for ctx.

Example This parser accepts any character (by advancing the StringScanner position), and returns a random number:

class RandomParser
  include Rsec
  def _parse ctx
    ctx.pos += 1
    rand
  end
end

p = RandomParser.new
p.parse '5' #=> a random number

Wait! Why bother? Feel the wrath of combinators!

p = /./.r.map { rand }

The parser is defined as a regex matching a single character (/./), converted into an Rsec token (.r); its result (map) is given as a random number (rand).