PROPOSAL: Restrict the type of (^), (^^), and add genericPower, genericPower'

[Ian Lynagh]

On Sat, Nov 17, 2007 at 01:00:51PM -0500, Cale Gibbard wrote:
> On 17/11/2007, Ian Lynagh <igloo at earth.li> wrote:
> > On Sat, Nov 17, 2007 at 11:45:52AM -0500, Cale Gibbard wrote:
> > > On 17/11/2007, Ian Lynagh <igloo at earth.li> wrote:
> > > >
> > > >     (^)          :: (Num a)             => a -> Int -> a
> > > >     genericPower :: (Num a, Integral b) => a -> b   -> a
> > >
> > > This is a move in the opposite direction from what I'd really like to
> > > see. The Int type is usually a premature optimisation, and I usually
> > > prefer to work with Integer as much as possible, but this just means
> > > more fromIntegral conversions (or the use of the awkwardly named
> > > general version).
> > >
> > > I would much prefer for length, !!, etc. to have more general types,
> > > not less general (with compiler specialisation on Int of course).
> >
> > This proposal is about making (^) and (^^) consistent with everything
> > else. Making everything use Integer rather than Int is an orthogonal
> > question.
> >
> > Someone could also make a Prelude.Integer module, that exports
> >     foo :: ... Integer ...
> >     foo = genericFoo
> > for various foo which are specialised to Int in Prelude, and reexports
> > all other functions from Prelude. Getting rid of implicit Prelude
> > imports would help too.
> 
> I don't want the types specialised to Integer either though. I'd want
> to have the types be as generic as possible, but include appropriate
> pragmas to tell GHC how to optimise when they're applied
> monomorphically.

You can also make Prelude.Generic
    foo :: Integral a => ... a ...
    foo = genericFoo
Or we could just remove the genericFoo functions and have
Prelude.Generic.foo be the canonical name.

If possible, I would like to separate what we should do /in general/
from whether we should make (^) and (^^) consistent with the rest of the
libraries, though. If someone wants to propose a change to the general
scheme /now/ then I don't mind this proposal waiting until that is
either resolved or fizzles out.


Thanks
Ian