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Date: Wed, 24 Feb 2010 08:38:47 +0100
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Subject: Re: [PHP-DEV] On closures and lamdba
From: mathieu.suen@easyflirt.com ("mathieu.suen")

Stanislav Malyshev wrote:
> Hi!
>
>> My question is not so much about implementation it is about language. I
>> have noticed quite a few times now that PHP developers use the word
>> "closure" when I would prefer "lambda".
>
> Everybody on the internet knows that Wikipedia is the ultimate source 
> of knowledge, and it says:
>
> In computer science, a closure is a first-class function with free 
> variables that are bound  in the lexical environment. Such a function 
> is said to be "closed over" its free variables.
>
> I think this describes what PHP is doing.
>
>> However, in the PHP manual as well as on this list, you seem to be
>> saying "closure" === "anonymous function" (which is what I'd rather see
>> called lambda).
>
> This is not entirely correct, you are right. There's a difference 
> between anonymous function and closure, though in practice in PHP 
> anonymous functions are closures (though some of them are rather 
> trivial ones with no variables to "close over") and that's now the 
> only way to do closure in PHP (i.e. you can't have non-anonymous 
> closure function).

I would rather say that PHP have both. Closure is just  a subset of 
lanbda. You say that a lambda is a closure whenever
the lambda capture variable from its outer scope.

You even have a special syntactic form to declare a lambda to be a 
closure, the keyword "use".

-- Mathieu

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