[Xmonad] xmonad-utils: small x apps for xmonad

[David Roundy]

On Wed, Aug 22, 2007 at 10:36:43PM -0400, Gwern Branwen wrote:
> On  0, Stefan O'Rear <stefanor at cox.net> scribbled:
> > On Wed, Aug 22, 2007 at 12:09:21PM -0400, Gwern Branwen wrote:
> > >      , ((modMask .|. shiftMask, xK_g     ), spawn $ "google" ++ unsafePerformIO(getSelection))
> > >
> > > But notice I used unsafePerformIO. The reason is that if you try to
> > > simply concatenate "google" and getSelection, there's a type mismatch.
> > > You can then try using liftM to do it, like ("google"++) `liftM`
> > > getSelection, and that will work well. Unfortunately, spawn :: String
> > > -> X (), so spawn needs to be lifted. (The internal /bin/sh stuff
> > > apparently requires a String too, so it's not spawn's fault.) But if
> > > you go 'spawn (("google"++) `liftM` getSelection' - which on its own
> > > would work - the resulting type is something like IO ( X ()). And that
> > > just can't be allowed inside 'keys'. At least, the only solution I
> > > could find was to just slice the Gordian knot and avoid introducing
> > > the IO signature in the first place. Monads may be the greatest thing
> > > since sliced bread, but most of the time they're just a pain :(
> >
> > It's a lot easier if you use the 'io' function, type forall a. IO a -> X a  :
> >
> > spawn . ("google " ++) =<< io getSelection
> >
> > Stefan
> 
> And as usual the experts chime in with 'Oh, that's easy!' :)
> 
> Yes, that works well. I didn't realize it was possible to convert an X ()
> to an IO () (which is what io is doing, if I understand correctly). Still
> don't quite understand the use of bind and composition, but it works, and
> obviates the need for xclip! Subjectively, it's also faster.

I'd say that io converts IO () to X ().  It's easier to read (I'd say) in
the notation:

  do selection <- io getSelection
     spawn ("google " ++ selection)
-- 
David Roundy
http://www.darcs.net
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