map -package:containers -package:bytestring -package:charset -package:aeson -package:foldl -package:psqueues -package:invertible -package:case-insensitive -package:blaze-html -package:ghc -package:dlist -package:filepath package:pipes
Apply a function to all values flowing downstream
map id = cat
map (g . f) = map f >-> map g
Apply a function to all values flowing downstream, and forward each
element of the result.
Apply a monadic function to all values flowing downstream
mapM return = cat
mapM (f >=> g) = mapM f >-> mapM g
Consume all values using a monadic function
(mapMaybe f) yields
Just results of
f.
Basic laws:
mapMaybe (f >=> g) = mapMaybe f >-> mapMaybe g
mapMaybe (pure @Maybe . f) = mapMaybe (Just . f) = map f
mapMaybe (const Nothing) = drain
As a result of the second law,
mapMaybe return = mapMaybe Just = cat