Data.Functor.Monadic

Helper functions for functors.

These operators are designed to make the interoperation between monadic and pure computations more convenient by allowing them to be chained together without peppering the program with superflouos return statements.

Each function is a pure analogue of a monadic one. The correspondences are as follows:

• >$> ~ >>= (bind)
• $> ~ >> (throw away left argument)
• <$ ~ << (re-exported from Data.Functor)
• <$< ~ =<< (same as <$>, but with the precedence of >>=)
• >=$> ~ >=> (Kleisli composition)
• <$=< ~ <=< (flipped Kleisli composition)

In addition, |> and .> are the left-to-right versions of $ and ., respectively.

Documentation

module Data.Functor

(>$>) :: Functor f => f a -> (a -> b) -> f b infixl 1

Flipped fmap for chaining plain functions after a functor in the following way:

readFile '1.txt' >$> lines >$> map length >>= print

lines and map length are non-monadic functions, but peppering them with returns, as pure >>= necessitates, is quite tedious.

In general:

m >>= return . f   is the same as   m >$> f

($>) :: Functor f => f b -> a -> f a infixl 1

Left-associatiative, flipped $>. Corresponds to >>

(<$<) :: Functor f => (a -> b) -> f a -> f b infixr 1

Right-associative infix synonym for fmap.

(>=$>) :: Functor f => (a -> f b) -> (b -> c) -> a -> f c infixl 1

Application of >$> to Kleisli composition >=> Use is analogous to that of >$>, e.g.

 f :: FilePath -> IO ()
 f = (readFile >=$> lines >=$> map length >=> print)
 

In general:

 m >=$> f   is the same as   m >=> return . f
 

(<$=<) :: Functor f => (b -> c) -> (a -> f b) -> a -> f c infixr 1

Flipped version of >=$>.

(|>) :: a -> (a -> b) -> b infixl 1

Flipped version of $.

(.>) :: (a -> b) -> (b -> c) -> a -> c infixl 1

Flipped version ..