I Need Help to construct an AST (abstract syntax tree ) in XML File

Question

I don't know how to solve this problem for home-work ; we are told to write a flex and bison code for a Language called Exp that offers structures control: sequence, condition and repetition. I wrote the code but I don't know how to construct an AST and display it on an XML file. Here is the Flex code :

START%{
        #include"parser.tab.h"

    %}

    lettre  [a-z]
    chiffre [0-9]

    %x comment
    %%


    "/*"                               BEGIN(comment);
    <comment>.                         ;
    <comment>"*/"                      BEGIN(INITIAL);

    debut                               return DEBUT;
    fin                                 return END;
    si                                  return IF;
    alors                               return ALORS;
    sinon                               return SINON;
    repeter                             return REPETER;
    jusqua                              return JUSQUA;
    pour                                return POUR;
    tantque                             return TANTQUE;
    lire                                return READ;
    ecrire                              return ECRIRE;

    " "|\t                             ;


    {lettre}({chiffre}|{lettre}){0,35}  {return ID;}
    "-"?{chiffre}+                      {return NUM;}
    "=="                                return EQUAL;

    "*"|"/"|"+"|"-"|"="|"<"|">"         return *yytext;
    "("|")"|","|";"|"."                 return *yytext;

    \n                                  ;

    .                                   {
                                        printf("erreur\n");
                                        return 0;
                                        }
    %%

and Here is Bison Code

 %{
        #include<stdio.h>


        extern FILE* yyin;

        int numAffec = 0;
        int numLecture = 0;
        int numEcriture = 0;
        int numnumCondition = 0;
        int numPour = 0;
        int numTantque = 0;
        int numRepeter = 0;
    %}


    %start prog
    %token DEBUT END IF ALORS SINON REPETER JUSQUA POUR TANTQUE READ ECRIRE NUM ID EQUAL
    %%

    prog : DEBUT seq_instr END '.'

    seq_instr : seq_instr instr ';'
            | instr ';'

    instr : instr_si           {numCondition++;}
            | instr_repeter    {numRepeter++;}
            | instr_pour       {numPour++;}
            | instr_tant_que   {numTantque++;}
            | instr_aff        {numAffec++;} 
            | instr_lect       {numLecture++;} 
            | instr_ecrit

    instr_si : IF exp ALORS seq_instr END 
            |  IF exp ALORS seq_instr SINON seq_instr END 
            ;


    instr_repeter : REPETER seq_instr JUSQUA '(' exp ')' 
                  ;               
    instr_pour : POUR '(' instr_aff ',' exp ',' instr_aff ')' seq_instr END 
                  ;  
    instr_tant_que : TANTQUE '(' exp ')' seq_instr END 
                   ; 
    instr_aff : ID '=' exp  
              ;  
    instr_lect : READ '(' ID ')'   
               ; 
    instr_ecrit : ECRIRE '(' exp ')'    
                ;
    exp : exp_simple '<' exp_simple
        | exp_simple '>' exp_simple
        | exp_simple EQUAL exp_simple
        | exp_simple

    exp_simple : exp_simple '+' term
                | exp_simple '-' term
                | term

    term : term '*' facteur
         | term '/' facteur
         | facteur

    facteur : '(' exp ')'
            | NUM
            | ID

    %%
    int main(int arg,char** var) {

        yyin = fopen(var[1],"r");

        if(yyin == NULL) {
            printf("erreur\n");
            return ;
        }

        yyparse();

        printf("Affectation    : %d\n",numAffec);
        printf("Lecture        : %d\n",numLecture);
        printf("Ecriture       : %d\n",numEcriture);
        printf("Conditionnel   : %d\n",numCondition);
        printf(" Pour    : %d\n",numPour);
        printf(" Tant Que: %d\n",numTantque);
        printf(" Repeter : %d\n",numRepeter);

        return 0;
    }

Answer 1

See https://stackoverflow.com/a/25106688/120163 for a general approach on building ASTs.

You'll need to tailor this to bison; in fact people do this all the time and IIRC, the bison reference manual gives examples on how to do this. So, you need to read the bison reference manual carefully.

Once you have an AST, you can produce XML from it by doing a recursive tree walk and spitting XML tags/content as you do the walk. This is a pretty trivial bit of code.