Variables in OCaml

In OCaml, variables are declared and used implicitly. The type system uses type inference to determine the types of variables in most cases.

(* In OCaml, we don't need to declare a main function explicitly *)

(* Let bindings are used to declare variables *)
let a = "initial"
let () = Printf.printf "%s\n" a

(* You can declare multiple variables at once using tuple destructuring *)
let b, c = 1, 2
let () = Printf.printf "%d %d\n" b c

(* OCaml will infer the type of initialized variables *)
let d = true
let () = Printf.printf "%b\n" d

(* Variables declared without initialization are not allowed in OCaml *)
(* Instead, we can use option types for potentially uninitialized values *)
let e : int option = None
let () = match e with
  | Some value -> Printf.printf "%d\n" value
  | None -> Printf.printf "None\n"

(* In OCaml, all bindings are immutable by default *)
(* To create a mutable binding, use the 'ref' keyword *)
let f = ref "apple"
let () = Printf.printf "%s\n" !f

To run the program, save it as variables.ml and use the OCaml compiler:

$ ocamlc -o variables variables.ml
$ ./variables
initial
1 2
true
None
apple

In OCaml:

Variables are declared using let bindings.
Multiple variables can be declared using tuple destructuring.
Type inference is used extensively, but you can also explicitly specify types.
There’s no concept of uninitialized variables; instead, OCaml uses option types for potentially absent values.
All bindings are immutable by default. To create mutable bindings, use the ref keyword.
The Printf.printf function is used for formatted output, similar to fmt.Println in the original example.

OCaml’s type system and immutability by default provide strong guarantees about program correctness at compile-time.

Values in OCaml

Constants in OCaml

Learn X By Example

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Variables in OCaml