.. _lexical_structure:


=================
Lexical Structure
=================

.. index:: single: lexical structure

-----------
Identifiers
-----------

.. index:: single: identifiers

Identifiers start with a alphabetic character or '_' followed by any number of alphabetic
characters, '_' or digits ([0-9]). Squirrel is a case sensitive language, this means that the
lowercase and uppercase representation of the same alphabetic character are considered
different characters. For instance "foo", "Foo" and "fOo" will be treated as 3 distinct
identifiers.

-----------
Keywords
-----------

.. index:: single: keywords

The following words are reserved words by the language and cannot be used as identifiers:

+------------+------------+-----------+------------+------------+-------------+
| base       | break      | case      | catch      | class      | clone       |
+------------+------------+-----------+------------+------------+-------------+
| continue   | const      | default   | delete     | else       | enum        |
+------------+------------+-----------+------------+------------+-------------+
| extends    | for        | foreach   | function   | if         | in          |
+------------+------------+-----------+------------+------------+-------------+
| local      | null       | resume    | return     | switch     | this        |
+------------+------------+-----------+------------+------------+-------------+
| throw      | try        | typeof    | while      | yield      | constructor |
+------------+------------+-----------+------------+------------+-------------+
| instanceof | true       | false     | static     | __LINE__   | __FILE__    |
+------------+------------+-----------+------------+------------+-------------+

Keywords are covered in detail later in this document.

-----------
Operators
-----------

.. index:: single: operators

Squirrel recognizes the following operators:

+----------+----------+----------+----------+----------+----------+----------+----------+
| ``!``    | ``!=``   | ``||``   | ``==``   | ``&&``   | ``>=``   | ``<=``   | ``>``    |
+----------+----------+----------+----------+----------+----------+----------+----------+
| ``<=>``  | ``+``    | ``+=``   | ``-``    | ``-=``   | ``/``    | ``/=``   | ``*``    |
+----------+----------+----------+----------+----------+----------+----------+----------+
| ``*=``   | ``%``    | ``%=``   | ``++``   | ``--``   | ``<-``   | ``=``    | ``&``    |
+----------+----------+----------+----------+----------+----------+----------+----------+
| ``^``    | ``|``    | ``~``    | ``>>``   | ``<<``   | ``>>>``  |          |          |
+----------+----------+----------+----------+----------+----------+----------+----------+

------------
Other tokens
------------

.. index::
    single: delimiters
    single: other tokens

Other used tokens are:

+----------+----------+----------+----------+----------+----------+
| ``{``    | ``}``    | ``[``    | ``]``    | ``.``    | ``:``    |
+----------+----------+----------+----------+----------+----------+
| ``::``   | ``'``    | ``;``    | ``"``    | ``@"``   |          |
+----------+----------+----------+----------+----------+----------+

-----------
Literals
-----------

.. index::
    single: literals
    single: string literals
    single: numeric literals

Squirrel accepts integer numbers, floating point numbers and strings literals.

+-------------------------------+------------------------------------------+
| ``34``                        | Integer number(base 10)                  |
+-------------------------------+------------------------------------------+
| ``0xFF00A120``                | Integer number(base 16)                  |
+-------------------------------+------------------------------------------+
| ``0753``                      | Integer number(base 8)                   |
+-------------------------------+------------------------------------------+
| ``'a'``                       | Integer number                           |
+-------------------------------+------------------------------------------+
| ``1.52``                      | Floating point number                    |
+-------------------------------+------------------------------------------+
| ``1.e2``                      | Floating point number                    |
+-------------------------------+------------------------------------------+
| ``1.e-2``                     | Floating point number                    |
+-------------------------------+------------------------------------------+
| ``"I'm a string"``            | String                                   |
+-------------------------------+------------------------------------------+
| ``@"I'm a verbatim string"``  | String                                   |
+-------------------------------+------------------------------------------+
| ``@" I'm a``                  |                                          |
| ``multiline verbatim string`` |                                          |
| ``"``                         | String                                   |
+-------------------------------+------------------------------------------+

Pesudo BNF

.. productionlist::
    IntegerLiteral : [1-9][0-9]* | '0x' [0-9A-Fa-f]+ | ''' [.]+ ''' | 0[0-7]+
    FloatLiteral : [0-9]+ '.' [0-9]+
    FloatLiteral : [0-9]+ '.' 'e'|'E' '+'|'-' [0-9]+
    StringLiteral: '"'[.]* '"'
    VerbatimStringLiteral: '@''"'[.]* '"'

-----------
Comments
-----------

.. index:: single: comments

A comment is text that the compiler ignores but that is useful for programmers.
Comments are normally used to embed annotations in the code. The compiler
treats them as white space.

The ``/*`` (slash, asterisk) characters, followed by any
sequence of characters (including new lines),
followed by the ``*/`` characters. This syntax is the same as ANSI C.::

    /*
    this is
    a multiline comment.
    this lines will be ignored by the compiler
    */

The ``//`` (two slashes) characters, followed by any sequence of characters.
A new line not immediately preceded by a backslash terminates this form of comment.
It is commonly called a *"single-line comment."*::

    //this is a single line comment. this line will be ignored by the compiler

The character ``#`` is an alternative syntax for single line comment.::

    # this is also a single line comment.

This to facilitate the use of squirrel in UNIX-style shell scripts.