Embedding Hygiene-Compatible Macros in an Unhygienic Macro System

It is known that the essential ingredients of a lisp-style unhygienic macro system can be expressed in terms of advanced hygienic macro systems. we show that the reverse is also true: we present a model of a core unhygienic macro system, on top of which a hygiene-compatible macro system can be built, without changing the internals of the core macro system and without using a code walker. to achieve this, the internal representation of source code as lisp s-expressions does not need to be changed. the major discovery is the fact that symbol macros can be used in conjunction with local macro environments to bootstrap a hygiene-compatible macro system. we also discuss a proof-of-concept implementation in common lisp and give historical notes.