[Haskell-beginners] Monad instances and type synonyms

[Brent Yorgey]

On Mon, Apr 15, 2013 at 09:51:11PM -0800, Christopher Howard wrote:
> On 04/14/2013 04:09 AM, Brent Yorgey wrote:
> > On Sat, Apr 13, 2013 at 05:03:57PM -0800, Christopher Howard wrote:
> > 
> > Sorry, what you're trying to do is simply not possible.  Type synonyms
> > must always be fully applied.  So if you want to make Adjustment an
> > instance of Monad then you have to make it a newtype.
> > 
> > However... Adjustment already *is* an instance of Monad!  (In
> > particular ((->) e) is an instance for any type e.)  So there's no
> > need for you to redeclare an instance yourself.  These days I think
> > you just have to import Control.Monad to bring the instance in scope.
> > 
> > -Brent
> > 
> 
> Thank you everyone for your patience. I believe what you say about it
> already being an instance of Monad, but I don't seem to have convinced
> the compiler:

What version of GHC do you have?  Try 'import Control.Monad.Instances'
in place of 'Control.Monad'.  The instances have moved but I don't
remember when.

-Brent