Maintainer  diagramsdiscuss@googlegroups.com 

Safe Haskell  SafeInfered 
Monoid and semigroup actions.
Documentation
Type class for monoid (and semigroup) actions, where monoidal
values of type m
"act" on values of another type s
.
Instances are required to satisfy the laws
act mempty = id
act (m1 `
mappend
` m2) = act m1 . act m2
Semigroup instances are required to satisfy the same law but with
'()' instead of mappend
. Additionally, if the type s
has
any algebraic structure, act m
should be a homomorphism. For
example, if s
is also a monoid we should have act m mempty =
mempty
and act m (s1 `
.
mappend
` s2) = (act m s1) `mappend
`
(act m s2)
By default, act = const id
, so for a type M
which should have
no action on anything, it suffices to write
instance Action M s
with no method implementations.
Action () l  
Action m s => Action (Option m) s 

Action (SM a) ()  
Action m n => Action (Split m) n  By default, the action of a split monoid is the same as for the underlying monoid, as if the split were removed. 
(Action a a', Action (SM a) l) => Action (SM a) (Option a', l)  
(Action (SM a) l2, Action l1 l2) => Action (a, l1) l2  
(Action m r, Action n r) => Action (:+: m n) r  Coproducts act on other things by having each of the components act individually. 