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#### 4.15.3.1 Grammar

Written by Eric Sunshine, sunshine@sunshineco.com.

The syntax for the standard Crystal Space map file is specified using a context-free grammar using a modified BNF (Backus-Naur Form) notation.

Terminal symbols (also known as tokens) are denoted like this, ``VERTEX`'. Non-terminal symbols are denoted in this fashion, vector. Expressions enclosed within `[' and `]' are optional. When an expression is followed by the notation `...', then the expression may appear zero or more times. Finally, the symbol '|' appearing between expressions indicates selection. Either the expression to the left may be utilized, or the one to the right, but not both. An example follows.

flip => ``HEAD`' | ``TAIL`'
wager => ``WAGER`' flip ``(`' money [ ``,`' money ... ] ``)`'

In this example, a ``WAGER'` may be followed by either ``HEAD'` or ``TAIL'`, and then by a parenthesized list of monetary values separated by commas. At least one monetary value must be specified. All subsequent values (including the comma) are optional, as denoted by `[' and `]'. Here are a couple of valid expressions which satisfy the wager production:

    WAGER HEAD (44)
    WAGER TAIL (5, 39, 2)

And here are a few invalid expressions which do not:

    WAGER HEAD (44,)
    WAGER TAIL (,23)
    WAGER TAIL ()
    WAGER EITHER (81, 15)
    WAGER (72, 91)

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