About this document
===================

**Note**: This document is a draft! Several of Nim's features may need more
precise wording. This manual is constantly evolving until the 1.0 release and is
not to be considered as the final proper specification.

This document describes the lexis, the syntax, and the semantics of Nim.

The language constructs are explained using an extended BNF, in which ``(a)*``
means 0 or more ``a``'s, ``a+`` means 1 or more ``a``'s, and ``(a)?`` means an
optional *a*. Parentheses may be used to group elements.

``&`` is the lookahead operator; ``&a`` means that an ``a`` is expected but
not consumed. It will be consumed in the following rule.

The ``|``, ``/`` symbols are used to mark alternatives and have the lowest
precedence. ``/`` is the ordered choice that requires the parser to try the
alternatives in the given order. ``/`` is often used to ensure the grammar
is not ambiguous.

Non-terminals start with a lowercase letter, abstract terminal symbols are in
UPPERCASE. Verbatim terminal symbols (including keywords) are quoted
with ``'``. An example::

  ifStmt = 'if' expr ':' stmts ('elif' expr ':' stmts)* ('else' stmts)?

The binary ``^*`` operator is used as a shorthand for 0 or more occurrences
separated by its second argument; likewise ``^+`` means 1 or more
occurrences: ``a ^+ b`` is short for ``a (b a)*``
and ``a ^* b`` is short for ``(a (b a)*)?``. Example::

  arrayConstructor = '[' expr ^* ',' ']'

Other parts of Nim - like scoping rules or runtime semantics are only
described in the, more easily comprehensible, informal manner for now.