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 | Chapter 1. Data Values |  |
| 1.7. Records | 1.8. Algebraic Data Types | 1.9. Closures |
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| | Chapter 1. Data Values | |
| 1.7. Records | 1.8. Algebraic Data Types | 1.9. Closures |
An Orc datatype is an algebraic data type, or "tagged union". A datatype value contains a sequence of values enclosed by a tag. This value can be matched by a pattern.
Datatypes are defined by a type declaration.
Each constructor
in the declaration introduces a new tag, followed by a sequence of slots.
The | separator allows multiple constructors to be defined at the same time.
In an untyped program, slots are written as _. In a typed program, slots contain types.
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Each constructor is a site, which takes one argument for each slot of the constructor, and publishes a datatype value consisting of the sequence of argument values, tagged with that constructor's unique tag.
Each constructor also has a corresponding unapply member,
which takes a value with that constructor's tag, removes the tag, and publishes the sequence of values as a tuple.
If its argument does not have the tag, it halts.
Thus, constructors can be used in pattern matching.
A datatype declaration defines a new sum type.
Each constructor defined by the datatype has the function type
lambda [ X0 , … , Xn ]( T0 , … , Tn ) :: S,
where Xi are the type parameters of the datatype, Ti are the types in the slots of the constructor,
and S is the sum type.
Each constructor also has a corresponding unapply member,
with type lambda [ X0 , … , Xn ](S) :: ( T0 , … , Tn ).
A datatype declaration may define a recursive type: the name of the type may be used in the definition of the type itself. In fact, this is the only way to declare a recursive type in Orc.
{- An enumeration, such as Java's enum, can be represented by a datatype whose constructors have no arguments. Note that an empty argument list, (), is still needed. -} type objective = Primary() | Secondary() | Tertiary() [Secondary(), Tertiary()] {- OUTPUT: [Secondary(), Tertiary()] -}
{- A Shape type with three data constructors -} type Shape = Rectangle(_, _) | Circle (_) def area(Rectangle(width,height)) = width * height def area(Circle(radius)) = 3.1415926535897 * radius ** 2 area(Rectangle(2, 3)) | area(Circle(1)) {- OUTPUT:PERMUTABLE: 6 3.1415926535897 -}
{- This is a binary tree datatype Leaf nodes carry integer values -} type Node = LeafNode(Integer) | InnerNode(Node, Node) {- Constructing a simple tree /\ 1 /\ 2 3 -} InnerNode(LeafNode(1),InnerNode(LeafNode(2),LeafNode(3))) {- OUTPUT: InnerNode(LeafNode(1), InnerNode(LeafNode(2), LeafNode(3))) -}
{- This is a binary tree datatype Leaf nodes carry values of type T -} type Node[T] = LeafNode(T) | InnerNode(Node[T], Node[T]) {- Constructing a simple tree /\ "A" /\ "B" "C" -} InnerNode[String](LeafNode("A"),InnerNode(LeafNode("B"),LeafNode("C"))) {- OUTPUT: InnerNode(LeafNode("A"), InnerNode(LeafNode("B"), LeafNode("C"))) -}
{- A datatype for optional values of type T -} type Option[T] = Some(T) | None() {- NONRUNNABLE -}
Related Reference Topics