It is possible to migrate code written in Emacs Lisp or another Lisp
dialect which uses dynamic scoping to a more modern programming
language with lexical scoping while largely preserving structure and
readability of the code. The biggest obstacle to such an idiomatic
translation from Emacs Lisp is the translation of dynamic binding
into suitable instances of lexical binding: Many binding constructs
in real programs in fact exhibit identical behavior under both
dynamic and lexical binding. An idiomatic translation needs to
detect as many of these binding constructs as possible and convert
them into lexical binding constructs in the target language to
achieve readability and efficiency of the target code.
The basic prerequisite for such an idiomatic translation is thus a
dynamic scope analysis which associates variable
occurrences with binding constructs. We present such an analysis.
It is an application of the Nielson/Nielson framework for flow
analysis to a semantics for dynamic binding akin to Moreau's. Its
implementation handles a substantial portion of Emacs Lisp, has been
applied to substantial realistic Emacs Lisp code, and is highly
accurate and reasonably efficient in practice.
