var.h

#ifndef VAR_H_
#define VAR_H_

#include <memory>
#include <string>
#include <unordered_map>

#include "string_piece.h"
#include "value.h"

using namespace std;

class Evaluator;
class Value;

class Var : public Evaluable {
 public:
  virtual ~Var();

  virtual const char* Flavor() const = 0;
  virtual const char* Origin() const = 0;
  virtual bool IsDefined() const { return true; }

  virtual void AppendVar(Evaluator* ev, Value* v);

  virtual string DebugString() const = 0;

 protected:
  Var();
};

class SimpleVar : public Var {
 public:
  SimpleVar(shared_ptr<string> v, const char* origin);

  virtual const char* Flavor() const {
    return "simple";
  }
  virtual const char* Origin() const {
    return origin_;
  }

  virtual shared_ptr<string> Eval(Evaluator*) const override {
    return v_;
  }
  virtual void Eval(Evaluator* ev, string* s) const override;

  virtual void AppendVar(Evaluator* ev, Value* v);

  string DebugString() const override;

 private:
  shared_ptr<string> v_;
  const char* origin_;
};

class RecursiveVar : public Var {
 public:
  RecursiveVar(Value* v, const char* origin);

  virtual const char* Flavor() const {
    return "recursive";
  }
  virtual const char* Origin() const {
    return origin_;
  }

  virtual void Eval(Evaluator* ev, string* s) const override;

  virtual void AppendVar(Evaluator* ev, Value* v);

  string DebugString() const override;

 private:
  Value* v_;
  const char* origin_;
};

class UndefinedVar : public Var {
 public:
  UndefinedVar();

  virtual const char* Flavor() const {
    return "undefined";
  }
  virtual const char* Origin() const {
    return "undefined";
  }
  virtual bool IsDefined() const { return false; }

  virtual void Eval(Evaluator* ev, string* s) const override;

  string DebugString() const override;
};

extern UndefinedVar* kUndefined;

class Vars : public unordered_map<StringPiece, Var*> {
 public:
  ~Vars();

  Var* Lookup(StringPiece name) const;

  void Assign(StringPiece name, Var* v);
};

#endif  // VAR_H_