From: William James <w_a_x_man@...>
Date: 2006-12-28T11:40:09+09:00
Subject: Re: Higher-Order Procedures Tutorial (long)

Nate Murray wrote:
> Hey Guys,
> I've been going through the video lectures "Structure and
> Interpretation of Computer Programs by Hal Abelson and Gerald Jay
> Sussman. " (
> http://swiss.csail.mit.edu/classes/6.001/abelson-sussman-lectures/ ).
> The section on Higher-Order Procedures was a huge eye-opener for me and
> I wanted to condense down what I learned in Lisp to guys who program in
> Ruby. Now I know that for most of the experienced on this list this
> will be old-news, but I hope to provide a valuable tutorial of Abelson
> and Sussman's material to some guys who are just learning about this
> stuff in Ruby.
>
> Posted below is the straight text and code examples of what I have so
> far. ( I've also posted the pdf of slides here:
> http://tech.natemurray.com/2006/12/higher-order-procedures-in-ruby.html
> if you're interested. ) Now, I am not just trying to drive up traffic
> to my site. My purpose in posting this here is two-fold:
>
> 1) To submit it for peer review. I'd like to know if you guys have any
> suggestions or improvements on the code examples and/or copy. For
> example a part that seems particularly ugly to me is the
>
>   cube = self.method(:cube).to_proc
>   cube.call(3)
>
> part. Any suggestions on how to make this a little more transparent or
> simplified?

def cube n
  n * n * n
end

def inc(n)
  n + 1
end

def sum(term, a, the_next, b)
  return 0 if a > b
  send(term,a) + sum(term, send(the_next,a), the_next, b)
end 

p sum( :cube, 1, :inc, 3 )