Maps a side effect over an InputStream.
mapM_ f s produces a new input stream that passes all output
from s through the side-effecting IO action f.
Example:
A version of map that discards elements
mapMaybe f s passes all output from s through the
function f and discards elements for which f s
evaluates to Nothing.
Example:
Contravariant counterpart to contramapMaybe.
contramap f s passes all input to s through the
function f. Discards all the elements for which f
returns Nothing.
Since: 1.2.1.0