Anonymous user
Monads/Maybe monad: Difference between revisions
Add OCaml
(Add OCaml) |
|||
Line 1,244:
none(string)
some("-1.10")</pre>
=={{header|OCaml}}==
The Option module already has our bind and return operations. If we wanted to redefine them :
<lang ocaml>let bind opt func = match opt with
| Some x -> func x
| None -> None
let return x = Some x</lang>
To easily manipulate bind, we can use infix operators and let pruning :
<lang ocaml>let (-->) = bind
let (let*) = bind
let print_str_opt x =
Format.printf "%s" (Option.value ~default:"None" x)</lang>
Example:
<lang ocaml>let safe_div x y = if y = 0.0 then None else return (x /. y)
let safe_root x = if x < 0.0 then None else return (sqrt x)
let safe_str x = return (Format.sprintf "%#f" x)
(* Version 1 : explicit calls *)
let () =
let v = bind (bind (safe_div 5. 3.) safe_root) safe_str in
print_str_opt v
(* Version 2 : with an operator *)
let () =
let v = safe_div 5. 3. --> safe_root --> safe_str in
print_str_opt v
(* Version 3 : let pruning really shine when inlining functions *)
let () =
let v =
let* x = safe_div 5. 3. in
let* y = if x < 0.0 then None else return (sqrt x) in
return (Format.sprintf "%#f" y)
in print_str_opt v</lang>
=={{header|Perl}}==
| |||