Copyright | (C) 2011-2015 Edward Kmett |
---|---|
License | BSD-style (see the file LICENSE) |
Maintainer | Edward Kmett <ekmett@gmail.com> |
Stability | provisional |
Portability | portable |
Safe Haskell | Trustworthy |
Language | Haskell2010 |
Extendable Functors
There are two ways to define an Extend
instance:
I. Provide definitions for extended
satisfying this law:
extended f . extended g = extended (f . extended g)
II. Alternately, you may choose to provide definitions for duplicated
satisfying this law:
duplicated . duplicated = fmap duplicated . duplicated
You may of course, choose to define both duplicated
and extended
.
In that case you must also satisfy these laws:
extended f = fmap f . duplicated duplicated = extended id
These are the default definitions of extended
and duplicated
.
class Functor w => Extend (w :: Type -> Type) where Source #
duplicated :: w a -> w (w a) Source #
duplicated = extended id fmap (fmap f) . duplicated = duplicated . fmap f
extended :: (w a -> b) -> w a -> w b Source #
extended f = fmap f . duplicated
Instances
gduplicated :: (Extend (Rep1 w), Generic1 w) => w a -> w (w a) Source #
Generic duplicated
. Caveats:
- Will not compile if
w
is a product type. - Will not compile if
w
contains fields where the type variable appears underneath the composition of type constructors (e.g.,f (g a)
).
Since: 5.3.8