code: func addBindings(a, b bindingFrame) bindingFrame {
  	result := make(bindingFrame)
  
  	for k, v := range a {
  		result[k] = v
  	}
  
  	for k, v := range b {
  		result[k] = v
  	}
  
  	return result
  }
docs: // Map union, b takes precedence when keys collide.