From: ptkwt@... (Phil Tomson)
Date: 2003-09-28T13:50:53+09:00
Subject: Re: Thoughts on yield

In article <87brt5wz83.fsf@ethereal.dyndns.org>,
Nolan J. Darilek <nolan_d@bigfoot.com> wrote:
>I've begun working on a music-related ruby project, and recently I've
>been pondering the idea of a music composition environment somewhat
>similar to cm, clm and friends for lisp, but in ruby instead.
>
>Today I was thinking about how ruby blocks make constructing
>domain-specific languages a snap. I've been reading Lisp as a Second
>Language at http://www.ircam.fr/equipes/repmus/LispSecondLanguage/, a
>Lisp tutorial for musicians, and was considering using a list-based
>structure for storing music. I sorta envisioned the language as
>looking something like:
>
>clef do
>  measure("4/4") do
>    c d e f g a b c
>    chord do
>      c e g
>    end
>  end
>end
>
>In this example, a-g are methods returning note objects.
>
>What I'd like is to have that return a list like so:
>
>["c", "d", "e", "f", "g", "a", "b", "c", ["c", "e", "g"]]
>


I played with this problem for a few minutes and this is what I came up 
with:

module Music

  def a(list=@notes)
    list << "a"
  end

  def b(list=@notes)
    list << "b"
  end

  def c(list=@notes)
    list << "c"
  end

  def d(list=@notes)
    list << "d"
  end
  
  def e(list=@notes)
    list << "e"
  end
  
  def f(list=@notes)
    list << "f"
  end
  
  def g(list=@notes)
    list << "g"
  end

  def clef
    puts "...In Clef..."
    yield
    return @notes
  end

  def measure(time)
    puts "...In Measure..."
    yield  
  end

  def chord
    puts "...In Chord..."
    yield @chord_notes
    @notes << @chord_notes
  end

  def notes
    @notes
  end
end

class Song
  include Music
  def initialize
    @notes = []
    @chord_notes=[]
  end
end

class MySong < Song
  include Music
  def initialize
    super
    clef do
      measure("4/4") do
        c; d; e; f; g; a; b; c;
        chord do |chrd|
          c(chrd); d(chrd); g(chrd); 
        end
      end
    end
  end
end

mysong = MySong.new
p mysong.notes

Of course, the ugly bit is the part in the chord block: you have to 
pass in 'chrd' to all of the a-g methods to get those notes to be added to 
the correct list (@chord_list) which then gets appended to the @notes 
list.  So it's still not quite what you want (I understand that you want 
people to see very little of the 'wizard behind the curtain' [Ruby] and 
having to pass 'chrd' sort of negates that).  Hopefully, someone else 
will offer a suggestion for getting rid of that requirement.

....you may not like the Song class bit I added either...

Phil