[Haskell] Why functional programming matters

[Simon Peyton-Jones]

Friends

Over the next few months I'm giving two or three talks to groups of *non* functional programmers about why functional programming is interesting and important.  If you like, it's the same general goal as John Hughes's famous paper "Why functional programming matters".

Audience: some are technical managers, some are professional programmers; but my base assumption is that none already know anything much about functional programming.

Now, I can easily rant on about the glories of functional programming, but I'm a biased witness -- I've been doing this stuff too long.  So this message is ask your help, especially if you are someone who has a somewhat-recent recollection of realising "wow, this fp stuff is so cool/useful/powerful/etc".

I'm going to say some general things, of course, about purity and effects, modularity, types, testing, reasoning, parallelism and so on. But I hate general waffle, so I want to give concrete evidence, and that is what I particularly want your help with.  I'm thinking of two sorts of "evidence":


1. Small examples of actual code. The goal here is (a) to convey a visceral idea of what functional programming *is*, rather than just assume the audience knows (they don't), and (b) to convey an idea of why it might be good.  One of my favourite examples is quicksort, for reasons explained here: http://haskell.org/haskellwiki/Introduction#What.27s_good_about_functional_programming.3F

But I'm sure that you each have a personal favourite or two. Would you like to send them to me, along with a paragraph or two about why you found it compelling?  For this purpose, a dozen lines of code or so is probably a maximum.


2. War stories from real life.  eg "In company X in 2004 they rewrote their application in Haskell/Caml with result Y".  Again, for my purpose I can't tell very long stories; but your message can give a bit more detail than one might actually give in a presentation.  The more concrete and specific, the better.  E.g. what, exactly, about using a functional language made it a win for you?


If you just reply to me, with evidence of either kind, I'll glue it together (regardless of whether I find I can use it in my talks), and put the result on a Wiki page somewhere.  In both cases pointers to blog entries are fine.

Quite a lot of this is FP-ish rather than Haskell-ish, but I'm consulting the Haskell mailing lists first because I think you'll give me plenty to go on; and because at least one of the talks *is* Haskell-specific.  However, feel free to reply in F# or Caml if that's easier for you.

Thanks!

Simon