[Haskell-cafe] Restricted type classes
sebf at informatik.uni-kiel.de
Sun Sep 5 10:11:44 EDT 2010
>> Just because we don't have
>> a use now doesn't mean it might not be useful in the future.
I am suspicious about complicating a design for potential future
However, difference lists provide an example of a type that support
Pointed more naturally than Applicative: the dlist package 
provides Applicative and Monad instances but only by converting to
normal lists in between.
Note that even fmap cannot be defined without converting difference
lists to normal lists in between. The natural interface to difference
lists would be Pointed (without a Functor superclass) and Monoid.
Underestimating the novelty of the future is a time-honored tradition.
More information about the Haskell-Cafe