1) I would use alias to ensure that atom? automatically picks up extensions to cons?, etc.

2) I've been experimenting with keeping prefix <- at the top-level, just to make globals salient. But this 'idiom' is less than 48 hours old; what do you think of it?

  <- carif (cons? & car)

  ern "The syntax `,@" expr " is invalid"

  (and list?.xs ~dotted?.xs)
  (append @cdr.args)
  (cons car.a (append cdr.a @cdr.args))

4) This is totally fine:

  (or (atom? cdr.x) (dotted? cdr.x))

  (or atom?:cdr.x dotted?:cdr.x)

5) I really like to use :else in multi-branch if.

6) There's a gotcha with multi-branch ifs: beware if you rely on paren insertion in test expressions:

  if nil
      car '(34 35)
     no nil
      cdr '(34 35)

  (if nil
      (car '(34 35))
      (no nil (cdr '(34 35))))

  (if
    no.args
      nil
    ~cdr.args
      car.args
    :else
      (let a car.args
        (if no.a
          (append @cdr.args)
          (cons car.a (append cdr.a @cdr.args)))))