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38 lines
1.5 KiB
Plaintext
About this document
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===================
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**Note**: This document is a draft! Several of Nim's features need more
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precise wording. This manual will evolve into a proper specification some
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day.
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This document describes the lexis, the syntax, and the semantics of Nim.
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The language constructs are explained using an extended BNF, in
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which ``(a)*`` means 0 or more ``a``'s, ``a+`` means 1 or more ``a``'s, and
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``(a)?`` means an optional *a*. Parentheses may be used to group elements.
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``&`` is the lookahead operator; ``&a`` means that an ``a`` is expected but
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not consumed. It will be consumed in the following rule.
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The ``|``, ``/`` symbols are used to mark alternatives and have the lowest
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precedence. ``/`` is the ordered choice that requires the parser to try the
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alternatives in the given order. ``/`` is often used to ensure the grammar
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is not ambiguous.
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Non-terminals start with a lowercase letter, abstract terminal symbols are in
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UPPERCASE. Verbatim terminal symbols (including keywords) are quoted
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with ``'``. An example::
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ifStmt = 'if' expr ':' stmts ('elif' expr ':' stmts)* ('else' stmts)?
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The binary ``^*`` operator is used as a shorthand for 0 or more occurrences
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separated by its second argument; likewise ``^+`` means 1 or more
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occurrences: ``a ^+ b`` is short for ``a (b a)*``
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and ``a ^* b`` is short for ``(a (b a)*)?``. Example::
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arrayConstructor = '[' expr ^* ',' ']'
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Other parts of Nim - like scoping rules or runtime semantics are only
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described in an informal manner for now.
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