patch for review: show ghci-related flags in ghci :set, :show packages, :show languages

[Claus Reinke]

>   - Overall, I like the additions, especially :show languages/packages

thanks!-) to complete ':show packages': is there a way to query 
(the linker, i guess?) about currently loaded packages?
 
>   - I wonder whether :set should show *all* the dynamic flags, rather than
>     just the GHCi-related ones?  Or perhaps just the flags that have
>     changed from their defaults?

the intention there is to let the user know which GHCi-specific
flags are available (see the current thread in haskell-cafe), as 
they are just another syntax for what might be GHCi options
(hugs :set gives current settings and brief help, all in one page).

perhaps there should be a separate ':show dynflags'? but
there are so many of them that one would need to control
the amount of output somehow, i guess. as i mentioned, 
being able to show import paths, etc, would also be useful.
 
>   - Move ghciFlags lower down, maybe as a local function to setCmd

the idea was to cache the small caf, instead of going through
all dynflags again and again. originally, i wanted to use that
list for helpText as well, but then decided to add the general
reference to the user's guide section instead.
 
>   - Any chance you could refactor runCommands to be 
>     a bit more readable? I find this style quite incomprehensible:
> 
>     maybe (return ())
>         (((bool (return ()) (runCommands getCmd)) =<<)
>           . ghciHandle handler . doCommand) mb_cmd
> 
>     eh? :-)

ah, yes. i had quite a bit of trouble figuring out the logic
of booleans, loops, returns, error handlers, etc in the original,
and this point-free style proved to be more amenable to
experimentation. but i agree, i will unfold this nest again!-)

will try to send updated patch later today,
claus