Re: converting this grammar to LL1

Try this (EBNF):


  E: P R .
  P: id | '&' id | '(' E ')' .
  R: [ Q R ] .
  Q: '=' E | '[' int ']' .


This should be LL1.






How to get there:


1) combine non-ambiguous parts to one production:
          E: P | E '=' E | E '[' int ']' .
          P: id | '&' id | '(' E ')' .


2) rewrite the ambiguous parts to a prefix and a suffix.
          E: P | E Q .
          Q: '=' E | '[' int ']' .


3) eliminate left recursion:
          E: P R .
          R: [ Q R ] .


All three modifications result in the grammer stated above.


HTH


Andi




Te-Cheng Shen schrieb:
>
> Hello:
> This is supposed to be really simple but I have worked on it for hours
> but all generated grammar are ambiguous and I am not sure why.
>
> This is the grammar
>
> E->id | &id | (E) | E[int] | E=E
>
> First of all, can this grammar make LL1? I am not sure.
>
> What I am doing is:
> Make this production
>
> E-> E = E
>
> to
>
> E -> F = E
> E -> F
>
> according to algorithms mentioned in textbook.
>
> Then the resulting grammar is
>
> E-> F = E
> E -> F
>
> F -> id| & id | ( E ) | E [ int ]
>
> then I apply another algorithm to eliminate left-recursions.
> then I apply another algorithm to left-factor this grammar.
>
> However, I use this tool LellRap to verify my resulted grammar. It is
> still ambiguous.
>
> Can anyone show me how to make it unambiguous?
>
> thanks a lot
>
> tcs


--
Andreas Gieriet mailto:andreas.gieriet@externsoft.ch
eXternSoft GmbH http://www.externsoft.com/
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