Do = Object.subtype(#Do);

Do.new(body, cond) {
    self = super.new();
    self.body = body;
    self.cond = cond;
    self;
}

Do.__eval__(env) {
    local result = self.body.__eval__(env);
    while (self.cond.__eval__(env)) {
        result = self.body.__eval__(env);
    }
    result;
}

Do.__codeon__(str) {
    str.push("do ");
    self.body.__codeon__(str);
    str.push(" while ( ");
    self.cond.__codeon__(str);
    str.push(" )");
}

// parse the grammar expression
// put it at the beginning of stmt (which is an alternation)
metaGrammar.stmt.prepend("\"whatever i want\" - b:stmt WHILE LPAREN c:expr RPAREN EOS { $$ = Do.new(b, c); }");

{

local i = 1;

    {

        whatever i want {
            i *= 2;
            print(i, "\n");
        } while (i < 1000);

        whatever i want {
            i *= 2;
            print(i, "\n");
        } while (i < 1000);

        whatever i want {
            i *= 2;
            print(i, "\n");
        } while (i < 1000);

    }

}