iter f m applies f to all bindings in map m.
f receives the key as first argument, and the associated value
as second argument. The order in which the bindings are passed to
f is unspecified. Only current bindings are presented to f:
bindings hidden by more recent bindings are not passed to f.
map f m returns a map with same domain as m, where the
associated value a of all bindings of m has been
replaced by the result of the application of f to a.
The order in which the associated values are passed to f
Same as Map.S.map, but the function receives as arguments both the
key and the associated value for each binding of the map.
valfold : (key -> 'a -> 'b -> 'b) -> 'a t -> 'b -> 'b
fold f m a computes (f kN dN ... (f k1 d1 a)...),
where k1 ... kN are the keys of all bindings in m,
and d1 ... dN are the associated data.
The order in which the bindings are presented to f is