Records in OCaml
Immutable named bundles with structural equality built in.
(* Records are immutable named bundles; with copies and updates. *)
type sighting = { species : string; count : int; pool : string }
let star = { species = "sea star"; count = 3; pool = "ledge" }
(* The with syntax copies, changing only what you name. *)
let more = { star with count = 5 }
let () =
Printf.printf "%s: %d in the %s pool\n" star.species star.count
star.pool;
Printf.printf "Recount: %d (original still %d)\n" more.count
star.count;
(* Structural equality comes free. *)
Printf.printf "Same sighting? %b\n" (star = { more with count = 3 })How it works
type sighting = { ... }declares the shape; construction names fields.{ star with count = 5 }copies, changing one field.=compares by value, not by reference.
Keywords and builtins used here
intletstringtypewith
The run, in numbers
- Lines
- 15
- Characters to type
- 556
- Tokens
- 107
- Three-star pace
- 65 tpm
At the three-star pace of 65 tokens a minute, this run takes about 99 seconds.
Step 1 of 3 in Types, step 15 of 29 in Language basics.