id,summary,reporter,owner,description,type,status,priority,milestone,component,version,resolution,keywords,cc,os,architecture,failure,difficulty,testcase,blockedby,blocking,related
3005,Normalize fully-applied type functions prior to display,dmcclean,chak,"I have a module with a matrix type constructor:
{{{
> data (Natural r, Natural c) => Matrix r c t = Matrix [[t]] deriving (Eq)
}}}
which uses type-level naturals to provide dimension checking.

A type class for multiplication:
{{{
> class Multiply a b where
>  type Product a b
>  times :: a -> b -> Product a b
}}}
and an instance for matrix multiplication:
{{{
> instance (Natural a, Natural b, Natural c, Num t) => Multiply (Matrix a b t) (Matrix b c t) where
>  type Product (Matrix a b t) (Matrix b c t) = Matrix a c t
>  times m1 m2 = ...
}}}
All of this works really well, I get dimension checking (and inference), and lot of other goodies.

My request has to do with the following GHCi session:
{{{
*Main> let a = matrix two two [[1,1],[2,6]]
*Main> :t a
a :: Matrix Two Two Integer
*Main> :t a `times` a
a `times` a :: Product
                 (Matrix Two Two Integer) (Matrix Two Two Integer)
}}}
When a type function is fully-applied, as Product is in this case, it would be nice if GHC could simplify it prior to display.

This would result in the following output for this example:
{{{
:t a `times` a
a `times` a :: Matrix Two Two Integer
}}}
I have attached the files necessary to run this test case, although a simpler one could be constructed.",feature request,closed,lowest,7.6.2,GHCi,6.10.1,fixed,,jpm@… pumpkingod@…,Unknown/Multiple,Unknown/Multiple,None/Unknown,Unknown,,,,