.. This document is designed for recording basic elements
.. Refer to https://golang.org/ref/spec

Lexical elements
----------------

Comments
~~~~~~~~

A single line comment can be achieved by using '//'.

Encoding
~~~~~~~~

Currently, ELI only supports ASCII.

Semicolons
~~~~~~~~~~

A semicolon may have two meanings

- Array dimension delimit.  It is a separator used in array indexing.  For example, ``arr[x;y]``;
- Multiple statement separator.  One line code with multiple statements is supported with semicolons.  The execution order of statements is from left to right, but within a statement, the execution order remains the same (from right to left).  For example, ``a<-!5;[]<-1+a``.

Identifiers
~~~~~~~~~~~

- An identifier starts with a letter;
- It can follow with arbitrary numbers and underscores('_');
- But, the last character cannot be an underscore

.. code-block:: none

	identifier ::= letter { letternum | underscore }
	underscore ::= {'_'} letternum
	letternum  ::= letter | [0-9]
	letter     ::= [a-zA-Z]

Keywords
~~~~~~~~

System commands (`Details <syscd.html>`_)

+----------+----------+----------+----------+
| )LOAD    | )SAVE    | )WSID    | )FNS     |
+----------+----------+----------+----------+
| )FLOAD   | )OUT     | )OFF     | )VARS    |
+----------+----------+----------+----------+

Operators
~~~~~~~~~

Please refer to the `primitive function <primt.html>`_ page.


Integer literals
~~~~~~~~~~~~~~~~

Currently, only decimal integers are supported.

.. code-block:: none

	int      ::= ['+' | '_'] decimals
	decimals ::= digit { digit }
	digit    ::= [0-9]


Floating-point literals
~~~~~~~~~~~~~~~~~~~~~~~

.. code-block:: none

	float    ::= decimals '.' decimals [exponent] | decimals exponent
	exponent ::= ('e' | 'E') ['+' | '_'] decimals

Examples

.. code-block:: none

	0.    //syntax error
	0.1
	2.3e5
	2.e5  //syntax error
	.1e3  //syntax error


Complex number literals
~~~~~~~~~~~~~~~~~~~~~~~

.. code-block:: none

	complex ::= real 'j' real
	real    ::= int | float

Examples

.. code-block:: none

	2j3
	2.3j4
	2j3.4


String literals
~~~~~~~~~~~~~~~

A string starts with a single quote(``'``).  The content can be any possible ASCII characters.  But if you want to include a single quote, you need to type two single quotes consecutively (i.e. ``''``).

.. code-block:: none

	string  ::= \' { content } \'
	content ::= letters | \'\'
	letters ::= all ASCII characters except \'

Examples

.. code-block:: none

	'It is a nice string'
	'It''s a nice string'

.. To be continued
.. - constants
.. - variables
.. - Types