val let* : ('a, 'e) t -> ('a -> ('b, 'e) t) -> ('b, 'e) tSyntax for bind.
val and* : ('a, 'e) t -> ('b, 'e) t -> ('a * 'b, 'e) tSyntax for both.
val let+ : ('a, 'e) t -> ('a -> 'b) -> ('b, 'e) tSyntax for map.
val and+ : ('a, 'e) t -> ('b, 'e) t -> ('a * 'b, 'e) tSyntax for both.