Monad.Basic3
type ('a, 'd, 'e) t
val bind : ('a, 'd, 'e) t -> f:('a -> ('b, 'd, 'e) t) -> ('b, 'd, 'e) t
val map : [ `Custom of ('a, 'd, 'e) t -> f:('a -> 'b) -> ('b, 'd, 'e) t | `Define_using_bind ]
val return : 'a -> ('a, 'b, 'c) t