datum.h

#ifndef _stran_datum_h_
#define _stran_datum_h_

#include "tok.h"

#include <cassert>
#include <unordered_map>

namespace stran {

struct datum;

struct env {
  env(const sp<env> &p) : parent(p) {}

  const sp<datum> &find(const std::string &name) const;

  void define(const std::string &name, const sp<datum> &val) {
    table[name] = val;
  }

private:
  std::unordered_map<std::string, sp<datum>> table;

  const sp<env> parent;
};

struct datum : tok, std::enable_shared_from_this<datum> {
  friend sp<datum> eval(const sp<datum> &p_d, const sp<env> &curr_env) {
    assert(p_d && "attempted to evaluate nil");
    return p_d->internal_eval(curr_env);
  }

private:
  // self-evaluating by default
  virtual sp<datum> internal_eval(const sp<env> &) {
    return shared_from_this();
  }
};

struct iden : datum {
  iden(const std::string &n) : name(n) {}

  const std::string name;

private:
  operator std::string() const override { return name; }

  sp<datum> internal_eval(const sp<env> &curr_env) override {
    return curr_env->find(name);
  }
};

struct inexact : datum {
  inexact(const double v) : val(v) {}

private:
  operator std::string() const override { return std::to_string(val); }

  const double val;
};

} // namespace stran

#endif