[Haskell-cafe] "hiddenness"

[Max Rabkin]

On Thu, May 14, 2009 at 10:51 PM, Vasili I. Galchin <vigalchin at gmail.com> wrote:
> Hello,
>
>      When I am compiling a module, I get "Could not find module
> 'Control.Module.State':
>                                                                   it is a
> member of package mtl-1.1.0.2, which is hidden"
>
>      1) What is the efficacy of "hiddenness"?

As I understand it, the purpose is two-fold. Firstly, if you have
multiple versions a package (or multiple packages containing the same
module), you can hide the ones not in use. Second, it ensures you have
declared all dependencies.

>      2) I have forgotten what tool I run to expose a package. ??

I've only ever had this when working with Cabal, where I have missed a
dependency. In this case, it looks like you have an undeclared
dependency on mtl. I'm not sure whether this arises in the non-Cabal
case.

>      3) In another vein, the code is using Data.Finitemap ... so I guess I
> must "darcs" install this?

I believe it was just uploaded to Hackage (it's obsolete, but useful
for getting old code to run).

HTH,
Max