From: Joel VanderWerf <vjoel@...>
Date: 2002-12-06T08:31:33+09:00
Subject: Re: [ANN] ratlast 0.1 -- embedded FORTH in Ruby

Mark Probert wrote:
> Hi, Harry.
> 
> Harry Ohlsen <harryo@zip.com.au> wrote: 
> 
>>On Fri, 6 Dec 2002 07:57, Mark Probert wrote:
>>
>>
>>>Most of all, it is a -lot- of fun to use!
>>>
>>>$ cat ex1.rb
>>>require 'Atlast'
>>>t = Atlast.new
>>>
>>>t.eval(": linear ( a b -- )  create swap , , does> dup >r @ * r> 4 + @
>>>+ ;") t.eval("3 17 linear aline") 
>>
>>Ah, yes, I can see how that's so much more intuitive than ...
>>
>>   def linear(x)
>>       3 * x + 17
>>   end
>>
> 
> hmmmmm.
> 
> Not quite.  The colon definition of linear is more like a lambda
> function in lisp, it defines a series of functions, for "a*x + b".
> The binding of a and b happens in the "linear aline" part.  I think
> you can do this in Ruby using closures.

But closures can do something quite different--they can share a variable 
binding with the enclosing scope:

a = 1
b = 2

linear = proc { proc {|x|a*x+b} }

l1 = linear[]

p l1[5] # ==> 7

a = 10

p l1[5] # ==> 52


If you want linear to behave more like the Forth example:

linear2 = proc { |aa,bb| proc {|x|aa*x+bb} }

l2 = linear2[1,2]

p l2[5] # ==> 7

aa = 10

p l2[5] # ==> 7