Thu, 28 Sep 1995 06:01:17 GMT

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need help with reg. expr., fsa khemani@eden.rutgers.edu (1995-09-28) |

Newsgroups: | comp.compilers |

From: | khemani@eden.rutgers.edu (Maverick) |

Keywords: | DFA, lex, question |

Organization: | Rutgers University |

Date: | Thu, 28 Sep 1995 06:01:17 GMT |

hi,

i have no idea where to post this question. i thought about posting it

here, since most course on compiler design discuss regular expressions,

finite state automaton, and bnf grammar.

my question is this:

1) let us say you have a grammar which describes comments. comments consist

of strings surrounded by /* and */ without intervening */, unless that */

appears in single quotes '*/'. assume that the alphabet contains the five

characters: a b ' / *

so /*ab'*/ and /*ab'*/'a*/ are proper comments

but /*ab'*/aa and /*ab*/a*/ are not proper comments.

i've constructed a non-deterministic fsa for this. i am not sure how to

construct a bnf grammar or regular expression for this language.

for the regular expression, i thought of

(/*)(a | b | / | * | '*/')* (*/)

but the problem is in the middle expression - how do you know if the

comment string has * / and then something else?

for bnf, the grammar i came up with has the same problem - i'm not sure

how to handle checking what has occured already - this is easier with

fsa.

2) write a regular expression for the set of binary numbers containing

3k 1's where k=1,2,3,... i need an fsa and ebnf (extended bnf) grammar

that recognizes this language.

general advice on how to handle these sort of problems would also be

greatly appreciated.

thanks much,

yash

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