Types

 

• The type constructors are before their type parameters, which are currified:

  Ocaml	Righteous
  int list	list int
  ('a, bool) Hashtbl.t	Hashtbl.t 'a bool
  type 'a foo =	type foo 'a =
  'a list list;;	list (list 'a);

• The abstract types are represented by a unbound type variable:

  Ocaml	Righteous
  type 'a foo;;	type foo 'a = 'b;
  type bar;;	type bar = 'a;

• Parentheses are required in t-uples of types:

  Ocaml	Righteous
  int * bool	(int * bool)

• In declaration of a concrete type, brackets must enclose the constructor declarations:

  Ocaml	Righteous
  type t = A of i | B;;	type t = [ A of i | B ];

• It is possible to make the empty type, without constructor:

      type foo = [];
  

• There is a syntax difference between data constructors with several parameters and data constructors with one parameter of type t-uple.

  The declaration of a data constructor with several parameters is done by separating the types with ``and''. In expressions and patterns, this constructor parameters must be currified:

  Ocaml	Righteous
  type t = C of t1 * t2;;	type t = [ C of t1 and t2 ];
  C (x, y);;	C x y;

  The declaration of a data constructor with one parameter of type t-uple is done by using a t-uple type. In expressions and patterns, the parameter has not to be currified, since it is alone:

  Ocaml	Righteous
  type t = D of (t1 * t2);;	type t = [ D of (t1 * t2) ];
  D (x, y);;	D (x, y);

• The predefined constructors ``True'' and ``False'' start with an uppercase letter.
• In record types, the keyword ``mutable'' must appear after the colon:

  Ocaml	Righteous
  type t = {mutable x : t1};;	type t = {x : mutable t1};