Hygienic macros are aware of what they are using. For example, if your macro uses leftpad, calling code does not need to import or be aware of leftpad. Also, co

Hygienic macros are aware of what they are using. For example, if your macro uses leftpad, calling code does not need to import or be aware of leftpad. Also, consider the issues around writing a swap macro using eval, how do you introduce a temporary which is guaranteed to not conflict with the caller’s code? Hygiene solves this by saying the macro’s temp variable is not the same as the calling code’s temp variable.