Type Declarations

Arbitrary Types

XCSL tries to emphasize modularity throughout system design, whenever possible. This principle is largely upheld by the internal data type system, especially the concept of Arbitrary Types.

Arbitrary types allow functions to be efficiently built for most generalized case. For example:

let sum x y = x + y

While many languages require parameters to be explicitly typed, XCSL recognizes that x and y can be any type that implements addition. This leads to a single modular sum function that can interchangeably add integers, real numbers, characters, and booleans.

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Type Aliases

It is frequently helpful to duplicate an existing type with an additional name, aka Alias. This allows code to be naturally self-documenting. Self-documenting code is a principle where internal functionality is made obvious via nomenclature. See a common example below:

type address = int

Memory addresses are integer values, where the integer itself does not matter, but rather the value in memory it points to. When working with addresses, it is better practice to label values as addresses rather than integers to distiquish memory pointers from data.

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Type Constructors

Type Constructors are used to define different instances of the same type of data.

See the following color example:

type color = Red | Green | Blue | RGB of (int; int; int)

Red, Green, and Blue are all valid constructors of the color type. Additionally, there is a constructor (RGB) that accepts three integer parameters. This set of constructors allows developers to quickly use common colors, as well as form new colors by mixing red, green, and blue.

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Complex Types

The aforementioned type constructors built simple type instances (e.g. no records). However, users are able to define Complex Types with records. See the following example using a person type.

type person =
    name   : string,
    age    : int,
    height : int 

Then, it can be called to create specific people.

const jim of person = 
    name = "jim",
    age = 21,
    height = 67

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