API for looking-up/retrieving Haddock comments?

[Simon Hengel]

> >I guess both items could be improved upon by extending GHCi to provide
> >an additional `:def` facility tailored to Haskell symbols allowing to
> >pass more meta-information (such as package and module information) into
> >the resulting command string... would something like that have any
> >chance of being accepted upstream?
> 
> I think it would make more sense to just add :doc to the GHCi
> front-end, relying on the user having already installed hoogle.  We
> could give a sensible error message if you don't have Hoogle
> installed.

I think it would be awesome if you could extend GHCi's functionality
with plug-ins.  Mainly, because it would make it easy to experiment with
ways to optimize your workflow.

One use case I have in mind is running Hspec tests from GHCi.  Currently
that requires me to:

(a) Reload the module:

   ghci> :reload

(b) Check the output for compile errors.

(c) Only if there were no compile errors, run the tests:

    ghci> hspec spec

Here it would be nice to have a custom :hspec command within GHCi, that
does all the required steps.  But GHCi's current mechanism for defining
commands is not powerful enough.  (It's possible to define a sequence of
commands, but it's not possible to check for the result of (a) and only
conditionally do (c)).