|
|
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 ``^`` or its last character
is ``>`` are right-associative, all other binary operators are left-associative.
Exception: The single "greater than" ``>`` operator is left-associative too.
Operators ending in ``>`` but longer than a single character are
called `arrow like`:idx:.
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 ``$(x.abc)``.
For binary operators that are not keywords the precedence is determined by the
following rules:
If the operator ends with ``=`` and its first character is none of
``<``, ``>``, ``!``, ``=``, ``~``, ``?``, it is an *assignment operator* which
has the lowest precedence.
Otherwise precedence is determined by the first character.
================ =============================================== ================== ===============
Precedence level Operators First character Terminal symbol
================ =============================================== ================== ===============
10 (highest) ``$ ^`` 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
================ =============================================== ================== ===============
Strong spaces
-------------
The number of spaces preceeding a non-keyword operator affects precedence
if the experimental parser directive ``#!strongSpaces`` is used. Indentation
is not used to determine the number of spaces. If 2 or more operators have the
same number of preceding spaces the precedence table applies, so ``1 + 3 * 4``
is still parsed as ``1 + (3 * 4)``, but ``1+3 * 4`` is parsed as ``(1+3) * 4``:
.. code-block:: nim
#! strongSpaces
if foo+4 * 4 == 8 and b&c | 9 ++
bar:
echo ""
# is parsed as
if ((foo+4)*4 == 8) and (((b&c) | 9) ++ bar): echo ""
Furthermore whether an operator is used a prefix operator is affected by the
number of spaces:
.. code-block:: nim
#! strongSpaces
echo $foo
# is parsed as
echo($foo)
This also affects whether ``[]``, ``{}``, ``()`` are parsed as constructors
or as accessors:
.. code-block:: nim
#! strongSpaces
echo (1,2)
# is parsed as
echo((1,2))
Only 0, 1, 2, 4 or 8 spaces are allowed to specify precedence and it is
enforced that infix operators have the same amount of spaces before and after
them. This rules does not apply when a newline follows after the operator,
then only the preceding spaces are considered.
Grammar
-------
The grammar's start symbol is ``module``.
.. include:: grammar.txt
:literal:
|