From: Daniel Brockman <daniel@...>
Date: 2005-08-04T12:46:31+09:00
Subject: Re: Closures

Gavin,

> I believe that Martin uses the term "closure" incorrectly

I agree.  This is a pet peeve of mine as well.  People seem
to think they sound smarter if they always say `closure'
instead of simply `function' or (in Ruby's case) `block'.

> A function that is a closure has access to the lexical
> scoping in which it was defined (the local variables).

I'd go further and say that a function that refers to its
lexical environment only becomes a closure when that
environment is removed from the stack.

(Otherwise, why not say that every expression that somehow
refers to its environment is a closure?)

In other words, if f and g are functions such that g refers
to some bindings in the lexical scope of f, then a closure
is formed when f returns but a reference to g survives.

Intuitively, I think of a closure as a function wrapped up
with its environment in a bubble floating off the stack.

(Of course, a single function body can be wrapped up into
multiple environments, yielding multiple separate closures.
Similarily, multiple functions can be wrapped up into the
same environment, yielding multiple closures that share a
single bubble.)

-- 
Daniel Brockman <daniel@brockman.se>

    So really, we all have to ask ourselves:
    Am I waiting for RMS to do this?   --TTN.