sqrt-either.cpp

// This... 
float sqrt(float x) {
  if (x < 0) {
    throw std::string("x should be >= 0");
  }
  return computeSqrt(x);
}

// ... can be transformed into this... 
Either<std::string, float> sqrt(float x) {
  if (x < 0) {
    return left("x should be >=0");
  }
  return right(computeSqrt(x));
}