OCaml Type

Checking

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

int

• 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.

float

• int_of_float
• float_of_int

char

• char_of_int
• int_of_char

string

• concatenation: ^
• "abc".[0]

type variable

• or generic/polymorphic
• 'a: unknown type

type variant

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

Polymorphic Variants

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)