22 Jun 2003 23:18:16 -0400

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From: | mefrill@yandex.ru (Vladimir) |

Newsgroups: | comp.compilers |

Date: | 22 Jun 2003 23:18:16 -0400 |

Organization: | http://groups.google.com/ |

Keywords: | parse, question |

Posted-Date: | 22 Jun 2003 23:18:16 EDT |

Hi,

I have a problem with FIRST function for 1 lookahead symbol evalation.

To lookup such the symbols for some nonterminal A I am doning follows:

1. go through all rules that left part is A. Here I do following:

a) If I have rule A --> aB, where a is terminal. I just add this

terminal to lookahead set for A.

b) If I have rule A --> e, where e is epsilon, I add e to lookahead

set for A.

c) If I have rule A --> B C ... where B - nonterminal, I at first

compute the lookahead set for B, if B's lookahead set contains

epsilon, check C and etc. I found that recursive function here is the

best. But I do not know how to work with rules like follows: A --> B,

B --> C A D... To compute lookahead set for A I have to at first

compute lookaheads for B, but if lookaheads for C contain epsilon I

need to know the same about A to understand do checking of D or

not...

Please, help to decide this problem and there may be the good FIRTS

computaion algorithm?

Thanks,

Vladimir.

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