Michael Wessel, arXiv:2305.02991, https://doi.org/10.48550/arXiv.2305.02991
I recently consulted for a very big Common Lisp project having more than one million lines of code (including comments). Let’s call it “System X” in the following. System X suffered from extremely long compilation times; i.e., a full recompile took about 33:17 minutes on a 3.1 GHz MacBook Pro Intel Core i7 with SSD and 16 GBs of RAM, using ACL 10.1. It turns out that a number of macros were causing an exponential code blowup. With these macros refactored, the system then recompiled in 5:30 minutes – a speedup by a factor of ~ 6. In this experience report, I will first illuminate the problem, and then demonstrate two potential solutions in terms of macro refactoring techniques. These techniques can be applied in related scenarios.
Notes on Refactoring Exponential Macros in Common Lisp Or: Multiple @Body Considered Harmful
Keywords: Common Lisp, Macros, Exponential Code Blowup, Macro Refactor- ing, Very Large Lisp Systems