A generic monadic transformation that maps over the immediate subterms
The default definition instantiates the type constructor c in
the type of gfoldl to the monad datatype constructor, defining
injection and projection using return and >>=.
Apply a function on every two successive elements of a stream. The
first argument of the map function is the previous element and the
second argument is the current element. When processing the very first
element in the stream, the previous element is Nothing.
Pre-release