[Haskell-cafe] [Alternative] summary of my understanding so far

[Matthew Farkas-Dyck]

On 15/12/2011, Gregory Crosswhite <gcrosswhite at gmail.com> wrote:
> 1) Documentation really needs to be improved
> 2) some/many cannot be physically separated from Alternative, but there
> *might* be an advantage to creating a subclass for them anyway purely for
> the sake of conveying more information about a type to users
> 3) Maybe and [] are sensible instances of Alternative, even if many/some
> often enters an infinite loop.
> 4) It is possible to provide special instance of many/some that satisfy the
> equations of many/some, with the slight disadvantage that these solutions
> are no longer the "least" solutions.
>
> Based on all of this, at this moment in time it seems to me that the most
> sensible way forward is to fix the documentation, tweak the definition of
> Alternative to no longer require the least solutions of the equations, and
> then to adopt the new instances for Maybe and [].
>
> Thoughts?

(1) If we do (4), then the documentation ought to be adequate as-is.
(2) In my opinion, no. If one is writing code polymorphic in
(Alternative f => f), then one needn't worry. If one is using such
code, then one ought to know whether some and many are sane for the
types in question, anyhow (O_ō)
(4) This is very reasonable; not the least solutions, but hey, they
converge (^_^)

> Cheers,
> Greg

Cheers,
Matthew Farkas-Dyck