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06617bbb76
Don't use ^ operator yet for compatibility with older compilers. Moved arrow like explanation, and fix precedence description on the text in the manual. Fixed typo in news.
110 lines
3.9 KiB
Plaintext
110 lines
3.9 KiB
Plaintext
Syntax
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======
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This section lists Nim's standard syntax. How the parser handles
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the indentation is already described in the `Lexical Analysis`_ section.
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Nim allows user-definable operators.
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Binary operators have 11 different levels of precedence.
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Associativity
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-------------
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Binary operators whose first character is ``^`` are right-associative, all
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other binary operators are left-associative.
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Precedence
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----------
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Unary operators always bind stronger than any binary
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operator: ``$a + b`` is ``($a) + b`` and not ``$(a + b)``.
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If an unary operator's first character is ``@`` it is a `sigil-like`:idx:
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operator which binds stronger than a ``primarySuffix``: ``@x.abc`` is parsed
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as ``(@x).abc`` whereas ``$x.abc`` is parsed as ``$(x.abc)``.
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For binary operators that are not keywords the precedence is determined by the
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following rules:
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Operators ending in either ``->``, ``~>`` or ``=>`` are called
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`arrow like`:idx:, and have the lowest precedence of all operators.
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If the operator ends with ``=`` and its first character is none of
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``<``, ``>``, ``!``, ``=``, ``~``, ``?``, it is an *assignment operator* which
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has the second lowest precedence.
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Otherwise precedence is determined by the first character.
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================ =============================================== ================== ===============
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Precedence level Operators First character Terminal symbol
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================ =============================================== ================== ===============
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10 (highest) ``$ ^`` OP10
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9 ``* / div mod shl shr %`` ``* % \ /`` OP9
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8 ``+ -`` ``+ - ~ |`` OP8
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7 ``&`` ``&`` OP7
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6 ``..`` ``.`` OP6
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5 ``== <= < >= > != in notin is isnot not of`` ``= < > !`` OP5
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4 ``and`` OP4
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3 ``or xor`` OP3
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2 ``@ : ?`` OP2
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1 *assignment operator* (like ``+=``, ``*=``) OP1
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0 (lowest) *arrow like operator* (like ``->``, ``=>``) OP0
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================ =============================================== ================== ===============
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Strong spaces
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-------------
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The number of spaces preceding a non-keyword operator affects precedence
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if the experimental parser directive ``#!strongSpaces`` is used. Indentation
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is not used to determine the number of spaces. If 2 or more operators have the
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same number of preceding spaces the precedence table applies, so ``1 + 3 * 4``
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is still parsed as ``1 + (3 * 4)``, but ``1+3 * 4`` is parsed as ``(1+3) * 4``:
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.. code-block:: nim
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#! strongSpaces
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if foo+4 * 4 == 8 and b&c | 9 ++
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bar:
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echo ""
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# is parsed as
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if ((foo+4)*4 == 8) and (((b&c) | 9) ++ bar): echo ""
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Furthermore whether an operator is used a prefix operator is affected by the
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number of spaces:
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.. code-block:: nim
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#! strongSpaces
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echo $foo
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# is parsed as
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echo($foo)
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This also affects whether ``[]``, ``{}``, ``()`` are parsed as constructors
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or as accessors:
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.. code-block:: nim
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#! strongSpaces
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echo (1,2)
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# is parsed as
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echo((1,2))
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Only 0, 1, 2, 4 or 8 spaces are allowed to specify precedence and it is
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enforced that infix operators have the same amount of spaces before and after
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them. This rules does not apply when a newline follows after the operator,
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then only the preceding spaces are considered.
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Grammar
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-------
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The grammar's start symbol is ``module``.
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.. include:: grammar.txt
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:literal:
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