From: Fearless Fool <r@...>
Date: 2011-03-23T05:27:13+09:00
Subject: Re: scope of assignments with lambda

7stud -- wrote in post #988636:
> How do recursive methods grab you?
> ...
> You might want to ponder the difference between your example and a
> recursive method.

@7stud: Pardon if I wasn't clear in my OP, but I was asking about
recursion.  [For the record, Lisp was one of my first programming
languages, and I often find it easier to think in terms of recursion
than in iteration.  I'd be more impressed if you wrote your factorial
routine as a lazy-eval'd stream, ala Abelson & Sussman SICP. ;)]

What I was surprised about was the scoping of variables in assignment
statements.  I guess it makes sense.  Assume that p is previously
undefined, then a reference on the RHS to p like this:

  p = p + 1

will raise an error.  But wrapped inside a lambda, the reference to p is
deferred, so it all works:

  p = lambda { |n| p.call(n-1) if (n > 0) }

As I said, that's the power of a lexical closure.

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