[Haskell-cafe] What *not* to use Haskell for

[Kyle Consalus]

On Tue, Nov 11, 2008 at 2:38 AM, Dave Tapley <dukedave at gmail.com> wrote:
> Hi everyone
>
> So I should clarify I'm not a troll and do "see the Haskell light". But
> one thing I can never answer when preaching to others is "what does
> Haskell not do well?"
>
> Usually I'll avoid then question and explain that it is a 'complete'
> language and we do have more than enough libraries to make it useful and
> productive. But I'd be keen to know if people have any anecdotes,
> ideally ones which can subsequently be twisted into an argument for
> Haskell ;)
>
> Cheers,
>
> Dave
>
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I think some would disagree with me, but I would advise against using
haskell for a task that
necessarily requires a lot of mutable state and IO and for which
serious performance is a big factor.
I'm not talking about stuff that can be approximated by zippers and
whatnot, but rather situations
where IORefs abound and data has identity. Haskell can quite capably
do mutable state and IO, but
if your task is all mutable state and IO, I'd lean toward a language
that makes it easier (OCaml, perhaps).

Also, I think there are some tasks which are more easily coded using
an OO approach, and while
this can be done in Haskell, I tend not to think it is worth the effort.
I've worked multiple projects in which big hierarchies of business
objects were used, and it had to be
easily to add new subclasses with minor variation and to treat any as
their parent. Considered by many in
FP community to be bad style, but I've never seen the equivalent
implemented in any other way effectively.
Haskell's record system gets in the way, as does the (as perceived by
me) esotericism of existential types.

Oh, also, any task that requires a good hash table. :-P

Mind you, Haskell is my first choice for a leisure project and I think
it is an excellent choice for
quite a few tasks and still capable of what I list above, just not in
my opinion the best choice.