From: Hiro Protagonist <credulity@...>
Date: 2008-10-30T03:57:47+09:00
Subject: Re: memoization example the ruby programming language question

Hiro Protagonist wrote:
> Hi all,
> 
> Attached is the example of memoization from the above book.
> 
> I am awed by ruby.
> 
> I understand what the program does in that I inserted puts  statements
> to follow it's logic.  It definitely caches the recursive calls.  In
> fact you can even enlarge the cache by asking for a larger factorial and
> the factorial Lambda Proc object will not do any unnecessary
> computations and use cached results if they exist.  For example if I
> initially do factorial.call(4) the results will be cached.  If I then do
> factorial.call(5) it will do a computation and use the factorial.call(4)
> cached result saving considerable amount of work.
> 
> I marked the line that I don't understand.  I want an explanation in
> terms of syntax.  If cache has data why is method memoize called first?
> I understand the initially recursive calls when cache is empty. In empty
> cache scenario the factorial lambda Proc keeps being called recursively
> until x == 0.  Once this happens memoize is called up the stack for each
> factorial call and data is cached for each value of x.  But when cache
> is full and momoization is used.  Why does it go to method memoize
> first?  I just don't see it syntactically.  This example may use some
> ruby 1.9 syntax.  I think factorial[x-1] is equivalent to
> factorial.call(x-1).
> 
> I need an explanation of syntax.  Also I have never seen the syntax:
> factorial = lambda {|x| return 1 if x==0; x*factorial[x-1]; }.memoize
> where the memoize method is attached to end of lambda {}.  Does
> factorial PROC object contain lambda block plus the appended memoize
> method?
> 
> I understand what it does but I am missing the syntax.
> 
> Thanks,
> pete
-------------------------
Thanks for explanation!!!  Boy I would never would have seen it. 
Insane!

I read the K&R The C Programming Language which to me is a tour de 
force.  Have not seen too many books of that caliber.  I would say this 
book, The ruby programming language, might be of that caliber.

I was never awed by objects I am not convinced they are as great as 
everybody says they are.  I come from a procedural language background. 
Even worked in assembler.  Ruby though impresses me !!!!

Thanks again,
Pete
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