^title Values

Values are the built-in atomic object types that all other objects are composed
of. They can be created through *literals*, expressions that evaluate to a
value. All values are *immutable*—once created, they do not change. The
number `3` is always the number `3`. The string `"frozen"` can never have its
character array modified in place.

## Booleans

A boolean value represents truth or falsehood. There are two boolean literals,
`true` and `false`. Their class is [Bool][].

[bool]: modules/core/bool.html

## Numbers

Like other scripting languages, Wren has a single numeric type:
double-precision floating point. Number literals look like you expect coming
from other languages:

    :::wren
    0
    1234
    -5678
    3.14159
    1.0
    -12.34

Numbers are instances of the [Num][] class.

[num]: modules/core/num.html

## Strings

A string is an array of bytes. Typically, they store characters encoded in
UTF-8, but you can put any byte values in there, even zero or invalid UTF-8
sequences. (You might have some trouble *printing* the latter to your terminal,
though.)

String literals are surrounded in double quotes:

    :::wren
    "hi there"

A handful of escape characters are supported:

    :::wren
    "\0" // The NUL byte: 0.
    "\"" // A double quote character.
    "\\" // A backslash.
    "\%" // A percent sign.
    "\a" // Alarm beep. (Who uses this?)
    "\b" // Backspace.
    "\f" // Formfeed.
    "\n" // Newline.
    "\r" // Carriage return.
    "\t" // Tab.
    "\v" // Vertical tab.

A `\u` followed by four hex digits can be used to specify a Unicode code point:

    :::wren
    System.print("\u0041\u0b83\u00DE") //> AஃÞ

A capital `\U` followed by *eight* hex digits allows Unicode code points outside
of the basic multilingual plane, like all-important emoji:

    :::wren
    System.print("\U0001F64A\U0001F680") //> 🙊🚀

A `\x` followed by two hex digits specifies a single unencoded byte:

    :::wren
    System.print("\x48\x69\x2e") //> Hi.

Strings are instances of class [String][].

[string]: modules/core/string.html

### Interpolation

String literals also allow *interpolation*. If you have a percent sign (`%`)
followed by a parenthesized expression, the expression is evaluated. The
resulting object's `toString` method is called and the result is inserted in the
string:

    :::wren
    System.print("Math %(3 + 4 * 5) is fun!") //> Math 23 is fun!

Arbitrarily complex expressions are allowed inside the parentheses:

    :::wren
    System.print("wow %((1..3).map {|n| n * n}.join())") //> wow 149

An interpolated expression can even contain a string literal which in turn has
its own nested interpolations, but doing that gets unreadable pretty quickly.

## Ranges

A range is a little object that represents a consecutive range of numbers. They
don't have their own dedicated literal syntax. Instead, the number class
implements the `..` and `...` [operators][] to create them:

[operators]: method-calls.html#operators

    :::wren
    3..8

This creates a range from three to eight, including eight itself. If you want a
half-inclusive range, use `...`:

    :::wren
    4...6

This creates a range from four to six *not* including six itself. Ranges are
commonly used for [iterating](control-flow.html#for-statements) over a
sequences of numbers, but are useful in other places too. You can pass them to
a [list](lists.html)'s subscript operator to return a subset of the list, for
example:

    :::wren
    var list = ["a", "b", "c", "d", "e"]
    var slice = list[1..3]
    System.print(slice) //> [b, c, d]

Their class is [Range][].

[range]: modules/core/range.html

## Null

Wren has a special value `null`, which is the only instance of the class
[Null][]. (Note the difference in case.) It functions a bit like `void` in some
languages: it indicates the absence of a value. If you call a method that
doesn't return anything and get its returned value, you get `null` back.

[null]: modules/core/null.html

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