From: max@gustavus.edu   
      
   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   
      
   --- SoupGate-Win32 v1.05   
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