[Haskell-cafe] Composing functions with runST

[Neil Mitchell]

Hi

> On the contrary, I think it's an excellent way of learning Haskell.
> I'm writing a lot of useful Haskell code with only one IO action
> (interact).  I don't think I could reasonably construct an
> introductory problem that couldn't be solved with it, and I haven't
> yet found an application for which I've needed more.

I think interact is a bit ugly. Most introductory problems are "take a
small amount of data, do something". In that case using Hugs/GHCi with
:main arguments to give in the arguments, getArgs to read them and
putStrLn to show the results is a very beautiful and does about all
that you need. Very few programs are actually interactive - if they
are they should usually get a GUI.

As for beginner issues with rank-2 types, I've been learning Haskell
for years now, and have never felt the need for a rank-2 type. If the
interface for some feature requires rank-2 types I'd call that an
abstraction leak in most cases. It certainly means that you can't
properly Hoogle for it, can't compile it with Yhc, can't do full type
inference etc.

Thanks

Neil