Re: [help-bison]How to stock information?

[soledady]

Le mercredi 20 juillet 2005 à 01:42 +0200, Hans Aberg a écrit :

thanks you very much for the quick answer!

> >  when I execute bison It builds a syntaxical tree (doesn't it?)
> 
> Not really. Bison supplies the constructs so that you can build a  
> syntax trees in the parser, bottom up, if you so want. One can't  
> immediately build them top-down.
> 
can i construct a top-down grammar?

> For example, if you have a rule
> term:
>    term "+" term {...}
> then $1, $2, and $3 will be used to assign values to the RHS  
> occurrences of "term", which can be forwarded to the LHS by the use  
> of $$. If you let $$ be the root of a tree, and $1, $2 and $3 be  
> branches attached to $$, you get a syntax tree:
>          $$
>       /  |  \
>      $1  $2  $3

 the $$ could be use again in other rule couldn't it?
 if yes then How?(not really in rule i mean in code next tne rule
between brackets) 
just a precision what the meaning of RHS and LHS(Right...? and Left
something?)



> > so for this part of an example (without all the rest of the example)
> > U{N}=U{N-1}+3*U{N-2}; U{0}=1; U{1}=2;
> > it's give me:
> > *3+    ;  1  2   =U{1}=U{0} U{n-2} U{n-1}    =U{N}
> >
> >
> > how can i do to recover correctly which number for which part of  
> > code ?
> 
> My guess is that you ask for the semantic value. It will be held in  
> the variables $$ and $k.
> 

ok but how can i do to know that *3+ means +3*
and to know which kind of term (u(n) or u(n+1) and so on...) are in use



> Also, there is a program <http://codeworker.free.fr/> dedicated to  
> this kind of task, you may want to have a look at.
> 
> >
> You just assign the suitable text values to the tokens, and start to  
> build suitable strings or macros. Assume you have
> 
> statement:
>    "{" statement_body "}"
> 
> statement_body: /* Builds "u(n)=u(n-1)+3*u(n-2);u{0}=1;u{1}=2;" */
> 
yes but how can i built this expression

> Then you need an action for "statement" like
>    statement: "{" statement_body "}" {
>      $$ = "begin Name=Suite; begin DEFINITION=RECURRENTE;" + $1 + ...
>    }
> where "+" is string concatenation. I hope you see the idea.
> 

ok  can we use $$ for other rule and recover its value, 
the idea is in the built of the grammar 

> You can simplify token handling by using Flex, and let every token  
> return the text that is lexed.
> 
>    Hans Aberg
> 
I thank you again. 
> 

> 
> 
> _______________________________________________
> address@hidden http://lists.gnu.org/mailman/listinfo/help-bison
>