ast visitor pattern

class AstExpression;
class AstCall;
class AstBinaryExpression;
class AstUnaryExpression;
class AstValueFloat;
class AstValueInt;
class AstVariable;

struct VisitorAst
{
    virtual ~VisitorAst();

    virtual void visit(AstExpression&) = 0;
    virtual void visit(AstCall&) = 0;
    virtual void visit(AstBinaryExpression&) = 0;
    virtual void visit(AstUnaryExpression&) = 0;
    virtual void visit(AstValueFloat&) = 0;
    virtual void visit(AstValueInt&) = 0;
    virtual void visit(AstVariable&) = 0;
};


struct StringifyAst:
    public VisitorAst
{
    std::string str;

    void visit(AstExpression&) override {}
    void visit(AstCall&) override {}
    void visit(AstBinaryExpression&) override;
    void visit(AstUnaryExpression&) override;
    void visit(AstValueFloat&) override;
    void visit(AstValueInt&) override;
    void visit(AstVariable&) override;
};