Haskell web applications using PHP as a "front end"

Question

There have been great things happening in the Haskell web development world, and some of the available frameworks (Yesod and Snap server) seem quite mature. However the learning curve can be a bit steep, and perhaps building web apps cannot quite be considered Haskell's forte.

The answer to another SO question of mine indicates that writing PHP extensions in Haskell should be possible. Infact I'm currently in the process of trying to convert a small Haskell program to a PHP extension as a proof of concept.

So, the question is - is there a case for creating a Haskell web framework that is meant to be run as a PHP extension and leaves all the request/response / cookies etc. handling to PHP?

What would be the design decisions involved in creating such a framework? Right now, the only thing I can think of is that it would probably expose an XML/JSON API accessible by the PHP pages using GET and SET function calls.

Answer 1

I can't think of a use case where this makes any sense. If you want something else to handle the HTTP request/response, you'd be better off writing to the Apache API directly.

Introducing PHP gives you argument parsing and cookie handling but also introduces a lot of other silliness. Not only are many of the common practices very unsafe or insecure, but you are limited to content generation -- if you want to dispatch to other parts of code based on the URL you have to write all that yourself. Many mature PHP programs end up just having one "start" PHP script. You also will have problems if you want to do anything interesting with uploaded files, because PHP handles that in a suboptimal way.

You could theoretically do something very processor intensive in your Haskell extension, but you might as well just write a C extension for PHP in that case. And PHP invocations are never supposed to hang around for very long anyway.

Seems like you are limiting yourself to PHP's brain-damaged model of a web application for the very trivial benefit of argument and header parsing.

Writing a Haskell interface to the Apache API could potentially be liberating. You could rely on a battle-tested web server, and also hook into every phase of the Apache request cycle. Apache's way of preforking and killing children every now and then might be a way of dealing with Haskell space leaks, although it's a sledgehammer approach.