From: Eric Hodel <drbrain@...7.net>
Date: 2006-11-29T10:17:02+09:00
Subject: Re: "yield" and "old-way iteration"

On Nov 28, 2006, at 1420 , Bjarke Walling wrote:
> I am writing a lexer and parser for a small language I have created.
> The first part splitting some input into tokens was easy to write  
> using
> "yield" (20 lines or so). I was actually a little overwhelmed how easy
> it was. The next part is to examine these tokens and parse them into
> language structures. I want to create a class with "current" and  
> "next"
> methods to get the current token and fetch the next (advance the
> pointer). I have solved it by using the first lexer yielding tokens  
> and
> collecting them in an array. Afterwards I can fetch tokens from the
> array. But could it be done in a smarter way?
>
> My code is like this:
>
> class FirstParse

     include Enumerable

>   def initialize
>     ...
>   end
>   def each
>     ... yield tokens ...
>   end
> end
>
> class SecondParse
>   def initialize
     def initialize(tokens)
>     @index = 0
       @tokens = tokens
>   end
>   def current
>     @tokens[@index]
>   end
>   def next
>     @index++
>     self.current
>   end
>   def read_structure1
>     ... read structures ...
>   end
>   def read_structure2
>     ... read structures ...
>   end
> end

parser = SecondParse.new FirstParse.new.to_a

Passing in an Array of tokens makes it easier to test, too.

-- 
Eric Hodel - drbrain@segment7.net - http://blog.segment7.net

I LIT YOUR GEM ON FIRE!