[Haskell-cafe] instance Monad m => Functor m
Hans Aberg
haberg at math.su.se
Wed Apr 9 10:48:22 EDT 2008
On 9 Apr 2008, at 16:26, Henning Thielemann wrote:
> I think a classical example are number sequences which can be
> considered as rings in two ways:
> 1. elementwise multiplication
> 2. convolution
>
> and you have some function which invokes the ring multiplication
>
> f :: Ring a => a -> a
>
> and a concrete sequence
>
> x :: Sequence Integer
>
> what multiplication (elementwise or convolution) shall be used for
> computing (f x) ?
For that problem to arise, one must have, when defining Sequence
class Ring (a; o, e, add, mult)
...
class (Ring(a; o, e, add, (*)), Ring(a; o, e, add, (**)) =>
Sequence a
It is a good question, but can be avoided by not admitting such
constructs. - I will think a bit more on it.
Hans
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