There is a discussion going on in php land about introducing closures and lambda functions, there was even a discussion on haskell-cafe about it (chx strikes again ;). About time, I would say. Having this functionality is a bonus. Having it implemented badly or half-arsed is going to do more damage than help. This is a short summary of what do I understand from the rfc and what do I think about it.

Intent

Create first class behaviours capable of storing state between use

Motivation

We want to maintain the history of computation, an maybe save and reuse the computation at a particular point in time

Implementation

The basic implementation is invisible in php - static variables in functions (but that doesn't allow us to have the usual features of a language with closures because functions in php are not first class objects, i.e we can't copy them), objects (they get us there, albeit more verbously). The examples below are borrowed from io-reader: php closures. Read the post and the full code to understand the full implementation.

Example

// fixed-point combinator function Y(Lambda &$le) { return lambda(get_defined_vars(), 'Lambda $f', ' return $f->call($f); ')->call(lambda(get_defined_vars(), 'Lambda $f', ' return $le->call(lambda(get_defined_vars(), \'$x\', \' return $f->call($f)->call($x); \')); ')); }

Note

Closures and objects are dual, compare behaviour with state and state with behaviours

Yet another note:

Alternatively have a look at this implementation or my emulating closures in php blurb

Final note:

All this is better avoided in php - too many underwater rocks