Traversing Z3_ast tree in C/C++

Question

In short, I need to be able to traverse Z3_ast tree and access the data associated with its nodes. Cannot seem to find any documentation/examples on how to do that. Any pointers would be helpful.

At length, I need to parse smt2lib type formulae into Z3, make some variable to constant substitutions and then reproduce the formula in a data structure which is compatible with another unrelated SMT sovler (mistral to be specific, I don't think details about mistral are important to this question but funnily enough it does not have a command line interface where I can feed it text formulae. It just has a C API). I have figured that to generate the formula in mistral's format, I would need to traverse the Z3_ast tree and reconstruct the formula in the desired format. I cannot seem to find any documentation/examples that demonstrate how to do this. Any pointers would be helpful.

Answer 1

Consider using the C++ auxiliary classes defined at z3++.h. The Z3 distribution also includes an example using these classes. Here is a small code fragment that traverses a Z3 expression. If your formulas do not contain quantifiers, then you don't even need to handle the is_quantifier() and is_var() branches.

void visit(expr const & e) {
    if (e.is_app()) {
        unsigned num = e.num_args();
        for (unsigned i = 0; i < num; i++) {
            visit(e.arg(i));
        }
        // do something
        // Example: print the visited expression
        func_decl f = e.decl();
        std::cout << "application of " << f.name() << ": " << e << "\n";
    }
    else if (e.is_quantifier()) {
        visit(e.body());
        // do something
    }
    else { 
        assert(e.is_var());
        // do something
    }
}

void tst_visit() {
    std::cout << "visit example\n";
    context c;

    expr x = c.int_const("x");
    expr y = c.int_const("y");
    expr z = c.int_const("z");
    expr f = x*x - y*y >= 0;

    visit(f);
}