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type 'a t = 'a option
let return (a: 'a): 'a t =
Some a
let fail: 'a t =
None
let (let* ) (m: 'a t) (f: 'a -> 'b t): 'b t =
match m with
| Some a ->
f a
| None ->
None
let (>>=) = (let* )
let (<*>) (f: ('a -> 'b) t) (a: 'a t): 'b t =
match f, a with
| Some f, Some a ->
Some (f a)
| _, _ ->
None
let map (f: 'a -> 'b): 'a t -> 'b t = function
| None ->
None
| Some a ->
Some (f a)
let to_list (m: 'a t): 'a list =
match m with
| Some a ->
[a]
| None ->
[]
let to_result (err: 'e): 'a t -> ('a, 'e) result = function
| None ->
Error err
| Some a ->
Ok a