OCaml Type

Jul 28, 2023

(123 : int);;
- : int = 33

(33 : bool);;
Error: This expression has type int but an expression was expected of type bool

• Range from $-2^{62}$ to $2^{62} - 1$
• one bit is used at runtime (Garbage Collector) to distinguish int from pointers
• OCaml library : Int64
• GitHub - ocaml/Zarith: The Zarith library implements arithmetic and logical operations over arbitrary-precision integers and rational numbers. The implementation, based on GMP, is very efficient.

• int_of_float
• float_of_int

• char_of_int
• int_of_char

• concatenation: ^
• "abc".[0]

• or generic/polymorphic
• 'a: unknown type

type t1 = C | D
type t2 = D | E
let x = D

type t = C1 [of t1] | ... | Cn [of tn]


type node = {value : int; next : mylist}
	and mylist = Nil | Node of node


type 'a mylist = Nil | Cons of 'a * 'a mylist

let rec length : 'a mylist -> int = function
  | Nil -> 0
  | Cons (_, t) -> 1 + length t

let empty : 'a mylist -> bool = function
  | Nil -> true
  | Cons _ -> false

Provide a type-safe way of doing something that might before have seemed impossible.
Variant types may mention their own name inside their own body

1. You don’t have declare their type or constructors before using them.
2. There is no name for a polymorphic variant type. (So another name for this feature could have been “anonymous variants”.)
3. The constructors of a polymorphic variant start with a backquote character.

let f = function
  | 0 -> `Infinity
  | 1 -> `Finite 1
  | n -> `Finite (-n)