val (>|=) : ('a, 'err) t‑> ('a‑>'b) ‑> ('b, 'err) t
val (>>=) : ('a, 'err) t‑> ('a‑> ('b, 'err) t) ‑> ('b, 'err) t
Monadic composition. e >>= f proceeds as f x if e is Ok x
or returns e if e is an Error.
val (<*>) : ('a‑>'b, 'err) t‑> ('a, 'err) t‑> ('b, 'err) t
a <*> b evaluates a and b, and, in case of success, returns
Ok (a b). Otherwise, it fails, and the error of a is chosen
over the error of b if both fail.