[erlang-questions] Similarities between web programming and functional programming

Jesper Louis Andersen <>
Sat Jun 12 22:37:17 CEST 2010


On Sat, Jun 12, 2010 at 10:19 PM, Nilanjan Raychaudhuri
<> wrote:
> Hi all,
>
> As a newbie into functional programming I am curious to know how functional programming style fits into building web applications? And how it
> compares to building web apps in Ruby or Java.
>
> Any pointer to article/literature will be helpful.

Look at the following function:

handle(Request) ->
  X = ...,
  Template = ...,
  render_response(?HTTP_OK, X, Template).

It has the specification contract
-spec handle(request()) -> response().

That is, handling incoming web requests are (sometimes pure) functions
from request() objects to response() objects. At this point, we are
essentially done. There isn't much more to it. Of course, we have only
defined a rough skeleton of how to do it, and a lot of the fleshy
details have been omitted. What makes it easy is that the web is
essentially stateless: All needed information is in the request()
object. If we store data locally, there will be some kind of token()
object (a cookie, say) in the request() object allowing us to get hold
of our server-side state. One could imagine calling another process to
get hold of this data (it is not much different from Ruby, Python or
Java calling into an SQL database for their data).

In general web-server handling is very amenable to the functional
programming paradigm. You may regard the above as being unnecessarily
low level, but it is very easy to use a couple of wrapper functions to
peel off layers of complexity so you end up with the innards of a web
framework such as Rails, Django or Pylons.

Erlang gives you an insane amount of tools to manipulate
web-applications. It seems that much of the heightened interest in
Erlang as of late is channeled towards building web-tools and webapps
in general. So not only will you have an excellent language for doing
web application development; you will also enjoy standing on the
shoulders of giants.


-- 
J.


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