avsm/result

OCaml Result Patterns

OCaml 5.x provides Result.Syntax for monadic chaining and Result.get_ok/Result.get_error for extraction.

Result.Syntax

Use open Result.Syntax to get let* and let+ bindings:

open Result.Syntax

let process request =
  let* req = validate request in
  let* auth = authenticate req in
  let* _ = authorize auth in
  execute req

DO NOT define local let ( let* ) = Result.bind. Use open Result.Syntax instead.

Extracting Values

| Function | Behavior on Error | |----------|-------------------| | Result.get_ok r | Raises Invalid_argument | | Result.get_error r | Raises Invalid_argument | | Result.value r ~default | Returns default |

Use Result.get_ok only when failure is a programming error:

(* Startup/config - crash on failure is intentional *)
let config = Result.get_ok (Config.load ())

(* Test setup - failure means test bug *)
let client = Result.get_ok (Tls.Config.client ~authenticator ())

Custom get_ok

Only define custom get_ok when you need different exception behavior:

(* Raises domain-specific Protocol_error instead of Invalid_argument *)
let get_ok = function
  | Ok x -> x
  | Error e -> raise (Protocol_error e)

If you just want Invalid_argument, use Result.get_ok directly.