Question

i have shared the header file containing class definition of a Context Free grammar for a parser. Could you comment on the design.
this code is for my lab assignment.
may be we could get some good programming tips out of this code. is the class hierarchy good or too complicated.

#ifndef CFG_H
#define CFG_H

#include <iostream>
#include <set>
#include <list>

using namespace std;



class Terminal;


class CfgSymbol
{
protected:
    char ch;
    set<Terminal*> first;
    set<Terminal*> follow;

public:
    CfgSymbol()
    {
        ch = '\0';
    }

    CfgSymbol(char c) : ch(c)
    {
    }

    virtual void computeFirst() = 0;
};


class Terminal: public CfgSymbol
{
private:

public:
    Terminal(): CfgSymbol()
    {
    }

    Terminal(char c) : CfgSymbol(c)
    {
        computeFirst();
    }

    virtual void computeFirst()
    {
        first->insert(this);
    }

};

class NonTerminal: public CfgSymbol
{
private:

public:
    virtual void computeFirst();
    virtual void computeFollow();
};

class SymbolString
{
public:
    CfgProduction* prd;
    list<CfgSymbol*> symstr;

    void computeFirst();
    void computeFollow();
};

class CfgProduction
{
private:
    NonTerminal lhs;
    SymbolString rhs;
public:
    int add_terminal(char t);
    int add_nonterminal(char n);
    int set_lhs(char c);
};

class Cfg
{
public:
    vector<CfgProduction*> prdList;

    void addProduction(const CfgProduction& cfg);
    void computeFirst();
    void computeFollow();
    void computeFirstFollow();

};

#endif

Answer 1

Spirit’s documentation should give you a nice intro for grammar implementation (with templates). Don’t know your level, maybe that’s too simple, but its quite interesting :

As a grammar becomes complicated, it
is a good idea to group parts into
logical modules. For instance, when
writing a language, it might be wise
to put expressions and statements into
separate grammar capsules. The grammar
takes advantage of the encapsulation
properties of C++ classes. The
declarative nature of classes makes it
a perfect fit for the definition of
grammars. Since the grammar is nothing
more than a class declaration, we can
conveniently publish it in header
files. The idea is that once written
and fully tested, a grammar can be
reused in many contexts. We now have
the notion of grammar libraries.