Applicative.Basic2_using_map2
type ('a, 'e) t
val return : 'a -> ('a, _) t
val map2 : ('a, 'e) t -> ('b, 'e) t -> f:('a -> 'b -> 'c) -> ('c, 'e) t
val map : [ `Define_using_map2 | `Custom of ('a, 'e) t -> f:('a -> 'b) -> ('b, 'e) t ]