matchM is:exact

matchM :: GraphM m gr => Node -> m (gr a b) -> m (Decomp gr a b)
fgl Data.Graph.Inductive.Monad
matchM :: (RegexContext regex source target, MonadFail m) => regex -> source -> m target
regex-base Text.Regex.Base.RegexLike
matchM :: Monad m => Cases a -> m a -> (a -> m b) -> m (Either a b)
selective Control.Selective, rebase Rebase.Prelude
Eliminate all specified values a from f (Either a b) by replacing each of them with a given f a.
matchM :: Monad f => f (Sigma t) -> (forall x . t x -> f (x -> a)) -> f a
selective Control.Selective.Multi
Every monad is a multi-way selective functor.
matchM :: Applicative f => (a -> f a) -> a -> f a
unipatterns UniPatterns
Try to run an effectful function, on pattern match fail behave like pure 
>>> matchM (\'a' -> Just 'A') 'a'
Just 'A'

>>> matchM (\'a' -> Just 'A') 'x'
Just 'x'