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diff --git a/doc/manual/syntax.txt b/doc/manual/syntax.txt new file mode 100644 index 000000000..0ae353edd --- /dev/null +++ b/doc/manual/syntax.txt @@ -0,0 +1,112 @@ +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 10 different levels of precedence. + +Relevant character +------------------ + +An operator symbol's *relevant character* is its first +character unless the first character is ``\`` and its length is greater than 1 +then it is the second character. + +This rule allows to escape operator symbols with ``\`` and keeps the operator's +precedence and associativity; this is useful for meta programming. + + +Associativity +------------- + +Binary operators whose relevant character is ``^`` are right-associative, all +other binary operators are left-associative. + +Precedence +---------- + +Unary operators always bind stronger than any binary +operator: ``$a + b`` is ``($a) + b`` and not ``$(a + b)``. + +If an unary operator's relevant character is ``@`` it is a `sigil-like`:idx: +operator which binds stronger than a ``primarySuffix``: ``@x.abc`` is parsed +as ``(@x).abc`` whereas ``$x.abc`` is parsed as ``$(x.abc)``. + + +For binary operators that are not keywords the precedence is determined by the +following rules: + +If the operator ends with ``=`` and its relevant character is none of +``<``, ``>``, ``!``, ``=``, ``~``, ``?``, it is an *assignment operator* which +has the lowest precedence. + +Otherwise precedence is determined by the relevant character. + +================ =============================================== ================== =============== +Precedence level Operators Relevant character Terminal symbol +================ =============================================== ================== =============== + 9 (highest) ``$ ^`` OP9 + 8 ``* / div mod shl shr %`` ``* % \ /`` OP8 + 7 ``+ -`` ``+ ~ |`` OP7 + 6 ``&`` ``&`` OP6 + 5 ``..`` ``.`` OP5 + 4 ``== <= < >= > != in notin is isnot not of`` ``= < > !`` OP4 + 3 ``and`` OP3 + 2 ``or xor`` OP2 + 1 ``@ : ?`` OP1 + 0 (lowest) *assignment 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: + |