Toy/types.md

Types

The type system in toy is opt-in, but allows a lot of robust checks at runtime when needed. Types themselves are first-class citizens. To retreive the type of an existing variable, use the typeof keyword.

print typeof value;

The types available are:

Type	Signature	Description
null	null	Represents a lack of any meaningful value, also has the type of "null"
boolean	bool	Either true or false
integer	int	Any whole number. The limits are implementation dependant
float	float	Any floating point number. The limits are implementation dependant
string	string	A series of characters, forming text
array	n/a	A series of values arranged sequentially in memory, indexable with an integer
array	n/a	A series of key-value pairs stored in a hash-table, indexable with the keys
function	fn	A chunk of reusable code, which can potentially return a value of some kind
type	type	The type of types
any	any	Can hold any value except null

Specifying Types For Variables

To specify a type for a variable, use : followed by the signature. In this example, the variable total can only ever hold integers:

var total: int = 0;

To specify the type of an array or dictionary, use some variation of these signatures:

var array: [int] = [1, 2, 3]; //an array of integers

var dictionary: [string : int] = ["key":42]; //a dictionary of key-value pairs

Complex, hard-to-write types can be stored in variables, like so:

//define a variable called "entry"
var entry: type = astype [string: [string]];

//define a phonebook which follows the above signature
var phonebook: entry = [
    "Lucy": ["1234", "Cabbage Ln"],
    "Bob": ["5678", "Candy Rd"]
];

Const

Const-ness, or the ability to fix the value of a variable, is part of the type system. To define a constant, follow the type signature with the const keyword:

var ANSWER: int const = 42; //answer will never change

You can also set the members of an array or dicitonary as const, or the entire compound:

var members: [int const] = [1, 2, 3]; //1, 2 and 3 cannot be changed, but "members" can be modified or re-assigned

var everything: [int] const = [4, 5, 6]; //everything is now const

Astype

Due to the syntax of Toy, when storing a complex type into a varable, you may need to use the astype keyword to differentiate the value from an array or dictionary.

var t: type = astype [int]; //t is a type, representing an array of integers
var u: type = [int]; //Error! it tried to assign an array with the sole entry "int"

First-Class citizens

Types are first-class citizens. What this means is that they can be used just like any other value, as well as being stored in variables, and even returned from functions.

fn decide(question) {
    if (question) {
        return int;
    }
    else {
        return float;
    }
}

var t = decide(true);

var number: t = 0; //what if it had been false?