Haskell Typeclasses

[Alex Martelli]

Kay Schluehr <kay.schluehr at gmx.net> wrote:
   ...
> work. Or maybe it works and I just have no clue how completely opaque
> call graphs as they appear in functions like this
> 
> def f(x):
>      h = g(x)
>      h()
> 
> can be tracked sufficiently in "register-time" in order to capture
> dependencies. It is not clear what h can be unless g is called and it
> might be as hard as type-inference or completely impossible to figure
> this out without executing g. If otherwise the checker can guarantee
> detection of a few obvious cycles where dependencies can be tracked
> also syntactically, at least in principle like in your example, what
> exactly is ensured by the checker and how can the definition of a
> typeclass be adapted accordingly? 

My preference would be to have the dependency tracker mark explicit
dependencies only; here, if this was in a typeclass with the appropriate
additions of self., I'd mark f as dependent on g only.  No real purpose
is served by allowing dependencies to be specified in a "cloaked" form,
anyway -- nor in going out of one's way to impede vigorous attempts by a
programmer to shoot himself or herself in the foot.


Alex