Parsing JSON with lex and yacc

json.l

%{
    #include<stdio.h>
    #include "y.tab.h"
    char *strclone(char *str);
    /*
    #define STRING "str"
    #define NUMBER "number"
    #define O_BEGIN "o_begin"
    #define O_END "o_end"
    #define A_BEGIN "a_begin"
    #define A_END "a_end"
    #define COMMA "comma"
    */
%}
DIGIT1to9 [1-9]
DIGIT [0-9]
DIGITS {DIGIT}+
INT {DIGIT}|{DIGIT1to9}{DIGITS}|-{DIGIT}|-{DIGIT1to9}{DIGITS}
FRAC [.]{DIGITS}
EXP {E}{DIGITS}
E [eE][+-]?
HEX_DIGIT [0-9a-f]
NUMBER {INT}|{INT}{FRAC}|{INT}{EXP}|{INT}{FRAC}{EXP}
UNESCAPEDCHAR [ -!#-\[\]-~]
ESCAPEDCHAR \\["\\bfnrt/]
UNICODECHAR \\u{HEX_DIGIT}{HEX_DIGIT}{HEX_DIGIT}{HEX_DIGIT}
CHAR {UNESCAPEDCHAR}|{ESCAPEDCHAR}|{UNICODECHAR}
CHARS {CHAR}+
DBL_QUOTE ["]
%%
{DBL_QUOTE}{DBL_QUOTE} |
{DBL_QUOTE}{CHARS}{DBL_QUOTE} {
    yylval=strclone(yytext);
    return STRING;
};
{NUMBER} {
    yylval=strclone(yytext);
    return NUMBER;
}
true {
    return true;
};
false {
    return false;
};
null {
    return null;
};
\{ {
    return O_BEGIN;
};

\} {
    return O_END;
};

\[ {
    return A_BEGIN;
};

\] {
    return A_END;
};

, {
    return COMMA;
};
: {
    return COLON;
};
. {
    printf("Unexpected: %c\nExiting...\n",*yytext);
    exit(0);
}
%%
char *strclone(char *str)
{
    int len = strlen(str);
    char *clone = (char *)malloc(sizeof(char)*(len+1));
    strcpy(clone,str);
    return clone;
}

json.y

%{
    #include<stdio.h>
    #include<string.h>
    #include<stdlib.h>
    #define YYSTYPE char*
    char *strconcat(char *str1, char *str2);
%}
%token NUMBER
%token STRING
%token true false null
%left O_BEGIN O_END A_BEGIN A_END
%left COMMA
%left COLON
%%
START: ARRAY {
    printf("%s",$1);
  }
| OBJECT {
    printf("%s",$1);
  }
;
OBJECT: O_BEGIN O_END {
    $$ = "{}";
  }
| O_BEGIN MEMBERS O_END {
    $$ = (char *)malloc(sizeof(char)*(1+strlen($2)+1+1));
    sprintf($$,"{%s}",$2);
  }
;
MEMBERS: PAIR {
    $$ = $1;
  }
| PAIR COMMA MEMBERS {
    $$ = (char *)malloc(sizeof(char)*(strlen($1)+1+strlen($3)+1));
    sprintf($$,"%s,%s",$1,$3);
  }
;
PAIR: STRING COLON VALUE {
    $$ = (char *)malloc(sizeof(char)*(strlen($1)+1+strlen($3)+1));
    sprintf($$,"%s:%s",$1,$3);
  }
;
ARRAY: A_BEGIN A_END {
    $$ = (char *)malloc(sizeof(char)*(2+1));
    sprintf($$,"[]");
  }
| A_BEGIN ELEMENTS A_END {
    $$ = (char *)malloc(sizeof(char)*(1+strlen($2)+1+1));
    sprintf($$,"[%s]",$2);
}
;
ELEMENTS: VALUE {
    $$ = $1;
  }
| VALUE COMMA ELEMENTS {
    $$ = (char *)malloc(sizeof(char)*(strlen($1)+1+strlen($3)+1));
    sprintf($$,"%s,%s",$1,$3);
  }
;
VALUE: STRING {$$=yylval;}
| NUMBER {$$=yylval;}
| OBJECT {$$=$1;}
| ARRAY {$$=$1;}
| true {$$="true";}
| false {$$="false";}
| null {$$="null";}
;
%%
int main()
{
   printf("\n");
   yyparse();
   printf("\n");
   return 0;
}
int yywrap()
{
   return 1;
}
char *strconcat(char *str1, char *str2)
{
    int len1 = strlen(str1);
    int len2 = strlen(str2);
    char *str3 = (char *)malloc(sizeof(char)*(len1+len2+1));
    strcpy(str3,str1);
    strcpy(&(str3[len1]),str2);
    return str3;
}