Q:

Error: expected specifier-qualifier-list before ‘TR’

I have a problem defining my structure inside the union on Bison
I made a structure 
typedef enum {Binary_Op,Uni_Op,Variable, Const} Tag_Type;

typedef struct tree
{
    Tag_Type Tag;
    union
    {
        struct
        {
            char op;
            struct tree *left, *right;
        }bin_op;

        struct
        {
            char op;
            struct tree *arg; /* negative or positive */
        }uni_op;

        char var;
        int const_val;
    }u;

}TREE_REC, *TR;

%}

%union
{

    int y_int;
    TR y_tree;
}

%type <y_tree> expr term factor assign
%token <y_int> CONST
%token <y_int> VAR

%%

but inside the union TR has an error. I don't understand why!! any help?

A:

You need to define struct tree and TR in a header file that you #include before you #include "y.tab.h".  The error message is telling you that you're trying to use TR before the compiler has seen a definition for it.

A:

I'm a bit confused with your typedef struct tree {...} TREE_REC, *TR. I would have rather written :
typedef struct tree {...} TREE_REC; //Alias on struct tree 
typedef TREE_REC * TR; //Definition of the pointer to a struct tree

The , in your typedef is disturbing me.
Can you test my solution, or just clarify the syntax of your typedef?

