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

[Hans Aberg]

On 19 Jul 2005, at 17:39, soledady wrote:

> if you receive for twice time this message i'm sorry i made a mistake

It it did come twice; I reply to the second address. [Please keep the  
cc to Help-Bison in replies, so that others can help.]

> Hello, i'm using Bison for compute a mathematic tool to resolve this
> kind of thing:
> u(n)=u(n-1)+3*u(n-2);u{0}=1;u{1}=2;
>  the example is very simple and this tools can do more things
> So the subject:
>  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.

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

>  how recover number (they could change of course) in a correct order
> cause i need to know how the formulation is written..
> i give you a parse of the code: (the print are just here in order  
> for me
> to understand how does it works)
>
> g    :    '=' d g            {printf("=");}
>         |U '{'N '}' g        {printf("U{N}");}
>         |U '{ N '-'NB'}'g       {printf("U{n-%d}",$5);}
>         |U '{' N '+' NB '}' g   {printf("U{N+%d}",$5);}
>         |U '{' NB '}' g        {printf("U{%d}",$3);}
>         |d g            {printf(" ");}
>         |V g            {printf(" ");}
>         |/*empty*/        {printf(" ")}
> d    :    g T             {printf(" ");}
>         |NB ';'            {printf(" %d ",$1);}
>
> T    :    /*vide*/        {printf("  ");}
>         |NB T            {printf("%d",$1);}
>         |'*' T            {printf("*");}
>         |'/' T            {printf("/");}
>         |'^' T            {printf("^");}
>         |'+' T            {printf("+");}
>         |'-' T            {printf("-");}
>         |';' T            {printf(";");}
> 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.

> more precisely i need to generate code in java and to do that i need
> which kind of fomulation its given?

My guess is that you want to write Java code to later be executed.  
Then you could write actions that output say strings for use in M4,  
or Guile, which would generate the Java output. It something similar  
for a program writing code in C++, and then it turned out to be  
tricky to place various C++ constructs, such as #include without at  
least a macro program. M4 is though tricky to use, therefore Guile  
might be better.

Also, there is a program <http://codeworker.free.fr/> dedicated to  
this kind of task, you may want to have a look at.

> thanks for your help!
>
> if you need more precision let's continue:
> moreover it's inside of a group of result globaly like that
>
> for this code:the indentation are here just to be clearer
> begin
>      Name=Suite;
>     begin
>      DEFINITION=RECURRENTE;
>      U{N}=U{N-1}+3*U{N-2};
>      U{0}=1;
>      U{1}=2;
>      TERME[1..8];
>      VARIATION;
>      TYPE;
>     SI_ARITH
>         begin
>          FORMULE_ARITH;
>          SOMME_ARITH[1..8];
>         end
>     SI_GEO
>         begin
>          FORMULE_GEO;
>          SOMME_GEO[1..8];
>         end
>      end
> end
>
>
> i'have this tree (the printf("blabla"); ) the indentation are here  
> just
> to be clearer

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;" */

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.

You can simplify token handling by using Flex, and let every token  
return the text that is lexed.

  Hans Aberg