[Haskell-cafe] collection monads

[tpledger at ihug.co.nz]

Matthias Fischmann wrote:
> > Do you expect the contained type x to change during a
> > sequence of monadic actions?  e.g. would you ever use
(>>=)
> > at the type 'Permutation Int -> (Int -> Permutation
Bool) ->
> > Permutation Bool'?
>
> no, i don't need that.  but aside from
> the fact that
>
> >     data Permutation k v =
> >         Permutation [(k, v)]
> >     instance (Ix k) =>
> >         Monad (Permutation k)
>
> is redundant (i think of the permutation
> as a function applicable to arbitrary
> lists): how would that change anything?
> my definition of return still doesn't
> work.  or how would you redefine
> 'return'?

Ah.  Yes, my approach falls over because it lacks two
things.  #1: a distinguished value of the Ix-constrained
type k, to pair off with return's argument.  #2: a purpose. 
I don't have a clear idea of what a do-block in a
permutation monad ought to mean.  Whoops!  <font
color=red>:-]</font>

Regards,
Tom (crawling back under his rock)