NOTE: I am not interested in using GCC statement expression!

I am implementing a set data structure using a Red Black Tree and to make it work for multiple types I am using macros.

This is a definition of a node:

typedef struct {
    bool colour;
    void* val;
    void* parent;
    void* left;
    void* right;
}* set;

I want to create a macro function set_contains(s, t), that will “return” a true expression if t is in a set s. By “return” I mean, that I can use it as such:

if(set_contains(my_set, 6)) {
    ...
}

For example, the following macro “returns” a true expression if x is an odd number:

#define isOdd(x)                        
    /* notice the lack of semicolon! */ 
    (bool)((x)&1)

My set_contains macro looks as follows:

#define set_contains(s, t)                                  
    do {                                                    
        set it = s;                                         
        while(it && *(typeof((t))*)it->val != (t)) {        
            if((t) < *(typeof((t))*)it->val) it = it->left; 
            else it = it->right;                            
        }                                                   
        /* This is what I want to "return" */               
        (bool)it;                                           
    } while(0)

How can I have (bool)it at the end of macro, so I can use the entire thing as an expression (like the isOdd macro)? The do while is necessary since I need to define a temp variable (it) to iterate over the set. Of course I cannot use it after while, since it is undefined in that scope. Once again, I want to achieve this without using GCC statement expression.