Hello,

- What is a use case for make-queue?  Especially with unspecified fill argument?

- In several places is specified that a function is O(n), but there's
no n in sight. While the intention is obvious, this should be made
explicit.

- make-queue-with-first-last: the arguments are named front and back,
in contrast with the function name and the rest of the description.

- queue-front and queue-back: the argument "element" is a mistake?

- queue-append: why not provide a function for appending queues
destructively, which can be implemented in O(number of queues)?

Cheers
P.