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Repetition

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Repetition operators specify that multiple occurrences of a term occur. The operators include the following:

  • ? indicates optionality, or in other words, that zero or one of the term is valid.

  • + indicates that one or more occurrences of the term are valid.

  • * indicates that zero or more occurrences of the term are valid.

  • #n where "n" is an integer, indicates that exactly n occurrences of the term are valid.

  • #n..m where "n" and "m" are integers and m is greater than n, indicates that between n and m occurrences of the term are valid.

  • #n.. where "n" is an integer, indicates that n or more occurrences of the term are valid.

Examples

These examples are taken from the grammars that define the “M” modeling language.

Optionality

This example states that when tokenizing the input stream, the DateLiteral token is inserted when the following tokens are recognized, in order:

  • An optional Sign token.

  • A DateYear token.

  • The literal "-".

  • A DateMonth token.

  • The literal "-".

  • A DateDay token.

        token DateLiteral = Sign? DateYear "-" DateMonth "-" DateDay;

One or More

This example states that when tokenizing the input stream, the Scientific token is inserted when the following tokens are recognized, in order:

  • A Decimal token.

  • The literal "e".

  • An optional Sign token.

  • One or more Digit tokens.

        token Scientific = Decimal "e" Sign? Digit+;

Zero or More

This example states that when tokenizing the input stream, the Binary token is inserted when the following tokens are recognized, in order:

  • The literal "0x".

  • Zero or more HexDigit tokens.

        token Binary = "0x" HexDigit*;

Range Operator Examples

The following examples show the different versions of this operator.

      // Recognizes exactly 5 "A"s : "AAAAA"
      token A5 = "A"#5;
      // Recognizes from 2 to 5 "A"s : "AA", "AAA", "AAAA", "AAAAA"
      token A5 = "A"#2..5;
      // Recognizes 3 or more "A"s : "AAA", "AAAA", "AAAAA"....
      token A5 = "A"#3..;
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