Racket's loops are almost always zero cost, and that is done by specifying the type you are iterating over (in-list, in-string etc). This is generally fine, si

Racket's loops are almost always zero cost, and that is done by specifying the type you are iterating over (in-list, in-string etc). This is generally fine, since when you want to iterate over something you probably already know it's type. That is done by macros and inlining. I wrote similar macros for guile, which has a very handy source to source optimiser.