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

On Sat, 17 Nov 2007, Cale Gibbard wrote:

On 17/11/2007, Ian Lynagh wrote:

...

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.

Thanks Ian

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.

As Ian pointed to, general types for exponents are rarely used in the code he explored. This is also my experience from doing math with Haskell. Did you make a different experience? The proposal isn't about removing the polymorphism of (^), but to shift it to an alphanumerically named function. I find "to have the types be as generic as possible" isn't always a good design strategy, especially in this case, where the type of the exponent cannot be infered from other operands. Thus in many cases the compiler has to choose a default type. It's just like I find (*) :: (Multiplyable a b c) => a -> b -> c not a good idea, say for various multiplications in linear algebra, because of lost type inference.