Applicative and Functor
ross at soi.city.ac.uk
Sat Mar 4 04:55:43 EST 2006
On Fri, Mar 03, 2006 at 07:14:16PM -0800, Ashley Yakeley wrote:
> Shouldn't Applicative be a subclass of Functor? "<$>" can then be dropped.
> [The Functor laws are implied by the Applicative laws]
It's the same old problem as with Monad, Functor and liftM (or indeed
with Monad, Applicative and return): that fine-grained hierarchies in
Haskell mean extra work for the programmer. You'd be forced to define a
Functor instance, even if all you wanted was pure and <*>. There have
been a series of proposed language changes to address this, the latest
being John Meacham's class synonyms. But less connected classes seem
to fit better with the current Haskell.
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