Thu, 16 Apr 2009 16:52:26 GMT

Related articles |
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[2 earlier articles] |

Re: additional regular expression operators zaimoni@zaimoni.com (2009-03-30) |

Re: additional regular expression operators haberg_20080406@math.su.se (Hans Aberg) (2009-03-30) |

Re: additional regular expression operators torbenm@pc-003.diku.dk (2009-03-31) |

Re: additional regular expression operators rpboland@gmail.com (Ralph Boland) (2009-03-31) |

Re: additional regular expression operators torbenm@pc-003.diku.dk (2009-04-14) |

Re: additional regular expression operators zayenz@gmail.com (MZL) (2009-04-15) |

Re: additional regular expression operators anton@mips.complang.tuwien.ac.at (2009-04-16) |

Re: additional regular expression operators gah@ugcs.caltech.edu (glen herrmannsfeldt) (2009-04-16) |

Re: additional regular expression operators torbenm@pc-003.diku.dk (2009-04-17) |

Re: additional regular expression operators mailbox@dmitry-kazakov.de (Dmitry A. Kazakov) (2009-04-17) |

From: | anton@mips.complang.tuwien.ac.at (Anton Ertl) |

Newsgroups: | comp.compilers |

Date: | Thu, 16 Apr 2009 16:52:26 GMT |

Organization: | Institut fuer Computersprachen, Technische Universitaet Wien |

References: | 09-03-111 09-03-123 09-04-001 |

Keywords: | lex |

Posted-Date: | 17 Apr 2009 06:10:59 EDT |

Ralph Boland <rpboland@gmail.com> writes:

*>I have never found a useful example of set intersection though.*

FP numbers are typically strings of digits and decimal points that

contain at least one digit and exactly one decimal point. That's a

little more elegant to describe as intersection than as a union; let's

use '&' as intersection operator:

[.0-9]*&.*[0-9].*&[^.]*[.][^.]*

That reflects exactly the specification above, which is not so clear

with the equivalent

[0-9]+[.][0-9]*|[.][0-9]+

Intersections can also be used for a set of things in arbitrary order

and also for a subset of things. For a set (i.e., your R @ S @ T):

(R|S|T)*&R~*RR~*&S~*SS~*&T~*TT~*

For a subset:

(R|S|T)*&R~*R?R~*&S~*S?S~*&T~*T?T~*

- anton

--

M. Anton Ertl

anton@mips.complang.tuwien.ac.at

http://www.complang.tuwien.ac.at/anton/

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