[ruby.parslet] Re: recursion without consuming a character

[Kaspar Schiess]

many ways to skin a cat.

   require 'parslet'
   require 'parslet/convenience'
   require 'pp'


   class MyParser < Parslet::Parser
     alias_method :`, :str
     rule(:word) { match['\w'].repeat(1).as(:word) }
     rule(:call) { (`()`).as(:call) }
     rule(:expression) {
       word >> call.repeat(1) ||
       word }
     root(:expression)
   end

   pp MyParser.new.parse_with_debug("f()()()")

repeat(1) is not equal to repeat and eliminates depth-searching where no 
solution exists. Think about your parser as though you were writing a 
top-down parser engine by hand, that helps usually. Longer parse rules 
must come before shorter ones, otherwise they wont get selected. And no, 
this wont be the killer argument for left recursion.

kaspar