[Haskell-cafe] Resource module

[Arie Peterson]

Dear list,


For some time, I have maintained a small private module centred around the
following type of "resource":

> newtype Resource cap m = Resource { with :: forall a. (cap -> m a) -> m
a }

Interpretation: @Resource cap m@ is a resource, providing a "capability"
of type @cap@, which does administration (like opening and closing handles)
in the monad @m at .

I would like to use a standard module instead of this howe-grown one, so I
can publish things that depend on it. Does anyone know a package that
provides this?


Things I tried:

- The type is suspiciously similar to the continuation monad transformer;
in fact @Resource cap m@ is isomorphic to @forall t. ContT t m cap at .
However, I can't use this latter type directly, because I would like
functions on Resources like the instance

> instance (Monoid cap) => Monoid (Resource cap m)

, which is not possible without a newtype wrapper.

- I tried using the "regions" package, since it has a very similar
purpose, but this seems impossible: some resources I could not express in
the form required for its class 'Resource' (methods 'open' and 'close').


If something like this is not yet around, I'll upload my version, but I'd
like to reuse, if possible.


Regards,

Arie