Re: cycle free grammar ?

ctx2002@gmail.com writes:
> I am currently learning how to write a compiler , i am using a book
> called Compilers Principles , techniques, and tools.
>
> in this book , there is an exercise asking write a algorithm to
> convert a grammar into a equivalent cycle - free grammar.
>
> for example:
>
> convert grammar s->ss|(s)|e to a cycle free grammar.
>
> any one know how to do that?


If you first make the grammar epsilon-free (which is the prior
exercise, if memory serves me), then the only kinds of cycles that can
remain are those based on productions of the form A -> B. That may be
enough of a hint to let you figure out the algorithm on your own. If
not, a second hint would be to look at algorithms for finding the
strongly connected components of directed graphs. -max

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