26 Jul 2005 13:21:57 -0400

Related articles |
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how to eliminate this left recursion hammeron56@yahoo.com (Mike) (2005-07-22) |

Re: how to eliminate this left recursion codeworker@free.fr (=?iso-8859-1?q?C=E9dric_LEMAIRE?=) (2005-07-26) |

Re: how to eliminate this left recursion cfc@shell01.TheWorld.com (Chris F Clark) (2005-07-26) |

Re: how to eliminate this left recursion owong@castortech.com (Oliver Wong) (2005-07-26) |

From: | "Oliver Wong" <owong@castortech.com> |

Newsgroups: | comp.compilers |

Date: | 26 Jul 2005 13:21:57 -0400 |

Organization: | GlobeTrotter |

References: | 05-07-083 |

Keywords: | parse |

Posted-Date: | 26 Jul 2005 13:21:57 EDT |

"Mike" <hammeron56@yahoo.com> wrote in message

*> I understand how to eliminate left-recursion when a grammar rule*

*> looks like this: a->ab | c*

*>*

*> but how do you do it when it looks only like this: a->ab*

If the expansion of "a" is "ab" with no other alternative, then you have an

infinite recursion that you can never get out of.

*> Such a grammar rule exists in the following regular expressions grammar*

*> (see rule ERE_expression)*

[snip]

*> ERE_expression : one_character_ERE*

*> | '^'*

*> | '$'*

*> | '(' extended_reg_exp ')'*

*> | ERE_expression ERE_dupl_symbol*

*> ;*

[snip]

Seems to me, this could be rewritten as:

ERE_expression : ( one_character_ERE

| '^'

| '$'

| '(' extended_reg_exp ')'

)

( ERE_dupl_symbol )*;

- Oliver

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