Solutions for this problem that I've used in my own S-expression config files: 1. Use only alists for maps because they prevent off-by-one errors. 2. Allow pl

Solutions for this problem that I've used in my own S-expression config files: 1. Use only alists for maps because they prevent off-by-one errors. 2. Allow plists because they're less verbose than alists and use reader macros to distinguish them, and allow the reader macro definitions to be in the same file. Most of the time I use option 1 because it's simpler.