The FunctorM library
ross at soi.city.ac.uk
Wed Mar 23 10:51:04 EST 2005
On Wed, Mar 23, 2005 at 09:49:43AM -0000, Simon Marlow wrote:
> Does anyone else have any comments on the suggestions from Iavor and
> Thomas in this thread? I'm happy to make changes, but only if there's
> a concensus. The proposals so far seems to be
> 1) add dist method
> 2a) make Functor a superclass of FunctorM
> 2b) make Functor a *sub*class of FunctorM
> 2c) make Functor a subclass of Monad
> 2d) make Functor a superclass of Monad
> 3) rename FunctorM class to ForEach
> 4) rename FunctorM module to Control.Monad.FunctorM(?)
> (1) is easy and not controversial (but is 'dist' the best name?).
fsequence:sequence = fmapM:mapM = fmap:map ?
As long as we remember that it's not always a distributive law (join
law fails, e.g. for ), and fmapM doesn't always define a functor
(doesn't preserve composition of Kleisli arrows).
2a) is needed to provide the default definition
fmapM f = fsequence . fmap f
2b-d) will break Haskell 98 programs.
The placement in the hierarchy is a bit wierd. Another possibility
(that you suggested earlier) is Data.Functor.
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