Nim/doc/manual/syntax.txt

Syntax
======

This section lists Nim's standard syntax. How the parser handles
the indentation is already described in the `Lexical Analysis`_ section.

Nim allows user-definable operators.
Binary operators have 11 different levels of precedence.



Associativity
-------------

Binary operators whose first character is ``^`` are right-associative, all
other binary operators are left-associative.

.. code-block:: nim
  proc `^/`(x, y: float): float =
    # a right-associative division operator
    result = x / y
  echo 12 ^/ 4 ^/ 8 # 24.0 (4 / 8 = 0.5, then 12 / 0.5 = 24.0)
  echo 12  / 4  / 8 # 0.375 (12 / 4 = 3.0, then 3 / 8 = 0.375)

Precedence
----------

Unary operators always bind stronger than any binary
operator: ``$a + b`` is ``($a) + b`` and not ``$(a + b)``.

If an unary operator's first character is ``@`` it is a `sigil-like`:idx:
operator which binds stronger than a ``primarySuffix``: ``@x.abc`` is parsed
as ``(@x).abc`` whereas ``$x.abc`` is parsed as ``$(x.abc)``.


For binary operators that are not keywords the precedence is determined by the
following rules:

Operators ending in either ``->``, ``~>`` or ``=>`` are called
`arrow like`:idx:, and have the lowest precedence of all operators.

If the operator ends with ``=`` and its first character is none of
``<``, ``>``, ``!``, ``=``, ``~``, ``?``, it is an *assignment operator* which
has the second lowest precedence.

Otherwise precedence is determined by the first character.

================  ===============================================  ==================  ===============
Precedence level    Operators                                      First character     Terminal symbol
================  ===============================================  ==================  ===============
 10 (highest)                                                      ``$  ^``            OP10
  9               ``*    /    div   mod   shl  shr  %``            ``*  %  \  /``      OP9
  8               ``+    -``                                       ``+  -  ~  |``      OP8
  7               ``&``                                            ``&``               OP7
  6               ``..``                                           ``.``               OP6
  5               ``==  <= < >= > !=  in notin is isnot not of``   ``=  <  >  !``      OP5
  4               ``and``                                                              OP4
  3               ``or xor``                                                           OP3
  2                                                                ``@  :  ?``         OP2
  1               *assignment operator* (like ``+=``, ``*=``)                          OP1
  0 (lowest)      *arrow like operator* (like ``->``, ``=>``)                          OP0
================  ===============================================  ==================  ===============


Whether an operator is used a prefix operator is also affected by preceding
whitespace (this parsing change was introduced with version 0.13.0):

.. code-block:: nim
  echo $foo
  # is parsed as
  echo($foo)


Grammar
-------

The grammar's start symbol is ``module``.

.. include:: ../grammar.txt
   :literal: