Composite type on OOFP 2025-26

Enumerated type

Mon, 01 Jan 0001 00:00:00 +0000

Enumerated type #

An enumerated type is a finite set of alternative values.

Example. A playing card can have one of four suits: Clubs, Diamonds, Hearts or Spades.

In the first assignment, we modeled these values as four characters 'C', 'D', 'H' or 'S'. This solution is unsatisfying, because the type Char allows other letters. Instead, we could declare an enumerated type (for instance named Suit) with 4 possible values (Clubs, Diamonds, Hearts and Spades).

Product type

Mon, 01 Jan 0001 00:00:00 +0000

Product type #

A product type can be viewed as a simplistic class, and its values as simplistic objects.

in Haskell #

Declaration #

Syntax. A product type can be declared as

Sum type

Mon, 01 Jan 0001 00:00:00 +0000

Sum type #

A sum type represents several alternative types.

in Haskell #

Syntax. A sum type in Haskell is declared as
data <sum type name> = <type 1> | ... | <type n>

Example. In the following declarations:

Point is a product type, and
Shape is a sum type.

-- a point in the Euclidean plane, represented by its coordinates
data Point = PointC Float Float

-- a shape, defined as either a triangle or a rectangle
data Shape = TriangleC Point Point Point | RectangleC Point Point Point Point

Note. in Haskell, an enumerated type is a sum type.