Anyone who had read the src of lalr-scm?

Anyone who had read the src of lalr-scm?

[康桥]

Hi all. I am a college student, recently I became interested in parser generating algorithms.
One of them is LALR(1).I took lalr-scm(which is mentioned in Guile Manual) as an example of the design of this kind of parser generators and studied its source code.
However, I found the source code too little scheme.It seems that it was written by a programmer who had been familier with C or Pascal before, mainly because it relies heaviliy on side-effects, which we don't use much in functional programming languages.
In spite of this, I read it almost all.I have found the part of computing itemsets, FOLLOW sets, etc.But I still leave one function not understand. It's function digraph in the macro lalr-parser in file lalr.scm.
It seems that this function is trying to traverse a digraph and make each FOLLOW set corresponding a vertex in the digraph the union of it and the FOLLOW sets corrsponding the vertices which can be reached from the vectex I mentioned before.But I can't figure out what algorithm it uses.

Anyone who know this algorithm?
BTW, should we rewrite lalr-scm in a more scheme way(even to make the process of parser generating slower)?

Re: Anyone who had read the src of lalr-scm?

[Thien-Thi Nguyen]

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() 康桥 <usakq12345@gmail.com>
() Fri, 06 Dec 2013 18:30:16 +0800

   But I still leave one function not understand.  It's function
   digraph in the macro lalr-parser in file lalr.scm.  It seems
   that this function is trying to traverse a digraph and make
   each FOLLOW set corresponding a vertex in the digraph the union
   of it and the FOLLOW sets corrsponding the vertices which can
   be reached from the vectex I mentioned before.  But I can't
   figure out what algorithm it uses.

   Anyone who know this algorithm?

At first glance it seems to be a standard fanout computation.
What do you mean by "know"?  Are you looking for its name?

   BTW, should we rewrite lalr-scm in a more scheme way(even to
   make the process of parser generating slower)?

Why don't you go ahead and try, then post your findings?

-- 
Thien-Thi Nguyen
   GPG key: 4C807502
   (if you're human and you know it)
      read my lisp: (responsep (questions 'technical)
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                     => nil

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