Сопрограммы на C++

#include <stdio.h>


class CharIter {
public:
  virtual ~CharIter() {}

  virtual char next() = 0;
};

class SimpleChain: public CharIter {
public:
  SimpleChain(const char *str)
    : m_str(str)
  {
    /* пусто */
  }

  virtual char next() {
    char result = *m_str;
    if (result) {
      ++ m_str;
    }
    return result;
  }

private:
  const char *m_str;
};

#define YIELD_RETURN(point, value) \
  m_state = point; \
  return (value); \
  case point:

class RLEDecode: public CharIter {
public:
  RLEDecode(CharIter *src)
    : m_src(src)
    , m_state(Start)
  {
    /* пусто */
  }

  virtual char next();

private:
  CharIter *m_src;

  enum State {
    Start, Normal, Repeat, End
  };
  State m_state;

  char m_current;
  int m_repeat;
};

char RLEDecode::next() {
  switch (m_state) {
    case Start:
    while (m_current = m_src->next(), m_current != '\0') {
      if (m_current == '!') {
        m_repeat = (unsigned char) m_src->next();
        m_current = m_src->next();
        while (m_repeat > 0) {
          YIELD_RETURN(Repeat, m_current);
          --m_repeat;
        }
      } else {
        YIELD_RETURN(Normal, m_current);
      }
    }

    while (true) {
      YIELD_RETURN(End, '\0');
    }
  }

  // компилятор ругается
  return '\0';
}

class Wrapper: public CharIter {
public:
  Wrapper(CharIter *src, int width)
    : m_src(src)
    , m_width(width)
    , m_state(Start)
  {
    /* пусто */;
  }

  virtual char next();

private:
  CharIter *m_src;
  int m_width;

  enum State {
    Start, InLine, NewLine, End
  };
  State m_state;

  char m_current;
  int m_col;
};

char Wrapper::next() {
  switch (m_state) {
    case Start:
    m_current = m_src->next();
    while (m_current != '\0') {
      for (
        m_col = 0;
        m_col < m_width && m_current != '\0';
        ++m_col, m_current = m_src->next()
      ) {
        YIELD_RETURN(InLine, m_current);
      }
      YIELD_RETURN(NewLine, '\n');
    }

    while (true) {
      YIELD_RETURN(End, '\0');
    }
  }

  // компилятор ругается
  return '\0';
}

int main() {
  const char *string =
    "12345678901234567890"
    "Hello, ten of A: !\12A, one bang: !\1!, 64 of x: !\100x.";

  SimpleChain source(string);
  RLEDecode rle(&source);
  Wrapper wrapper(&rle, 20);

  char current;
  while (current = wrapper.next(), current != '\0') {
    printf("%c", current);
  }

  return 0;
}