FWIW Racket has two types of cons cells: mutable and immutable. And if you know what you are doing - then you can abuse the FFI to mutate the immutable ones (bu

FWIW Racket has two types of cons cells: mutable and immutable. And if you know what you are doing - then you can abuse the FFI to mutate the immutable ones (but don't tell anyone) using unsafe-set-mcar! and unsafe-set-mcdr!.