environment.hpp

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#ifndef ENVIRONMENT_HPP
#define ENVIRONMENT_HPP

// system includes
#include <map>

// module includes
#include "atom.hpp"
#include "expression.hpp"

typedef Expression (*Procedure)(const std::vector<Expression> & args);

class Environment {
public:
  Environment();

  bool is_known(const Atom &sym) const;

  bool is_exp(const Atom &sym) const;

  Expression get_exp(const Atom &sym) const;

  void add_exp(const Atom &sym, const Expression &exp);

  bool is_proc(const Atom &sym) const;

  Procedure get_proc(const Atom &sym) const;

  void reset();

private:
  
  // Environment is a mapping from symbols to expressions or procedures
  enum EnvResultType { ExpressionType, ProcedureType };

  struct EnvResult {
    EnvResultType type;
    Expression exp; // used when type is ExpressionType
    Procedure proc; // used when type is ProcedureType

    // constructors for use in container emplace
    EnvResult(){};
    EnvResult(EnvResultType t, Expression e) : type(t), exp(e){};
    EnvResult(EnvResultType t, Procedure p) : type(t), proc(p){};
  };

  // the environment map
  std::map<std::string, EnvResult> envmap;
};

#endif