I think it's more realistic to use lens style Setters where possible.
Essentially:
type Setter s t a b = (a -> b) -> s -> t
type Setter' s a = Setter s s a a
bytes :: Setter ByteString Word8
bytes = BS.map
fmapped :: Functor f => Setter (f a) (f b) a b
fmapped = fmap
In this framework, you could write a function that can abstract over any
setter, eg.
changeSomething :: Setter s t Foo Bar -> s -> t
changeSomething s = s fooBar
where fooBar :: Foo -> Bar
It's not quite the same thing as making ByteString or Text an instance
of Functor, but for some tasks, it can be a good replacement.
On Sun, 01 Mar 2015 02:08:40 +0100, silvio
Wow ConstraintKinds. There's always a new extension to be learned :) Anyway, if changing the Functor declaration were allowed, it would probably make more sense to use something like MonoFunctor. Unfortunately, MPTC or type family stuff is never going to make it into Prelude.
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