Drinkable Chicken

You know R5RS's case construct? It works much like case/switch statements in other languages, except it has more parentheses: ;-)

#;6> (define language 'chicken)
#;7> (case language
--->   ((c c++ java) "bleh")
--->   ((python perl ruby) "better")
--->   ((chicken scheme) "cool")
--->   (else "never heard of it"))
"cool"

Now, yesterday there was an interesting question in chicken-users. The following code works:

#;8> (define foo 'a)
#;9> (case foo
--->   ('a 3)
--->   (else 4))
3

Does that mean that Chicken's case accepts qualifiers other than lists? Actually, no. Here's a hint:

#;10> (define bar 'quote)
#;11> (case bar
---->   ('a 3)
---->   (else 4))
3

As it turns out, 'a expands to (quote a), so it *is* a list, and therefore "correct", in the sense that case treats it like a list containing the symbols quote and a. (Which is not what was intended, but it *is* valid.)

Too bad, the following does not work:

#;13> (define cool-names '(guido larry matz felix))
#;14> (case 'bill
---->   (cool-names "cool!")
---->   (else "uncool"))
Error: (map) during expansion of (case ...) -
 argument is not a proper list: cool-names

Inspecting a case construct with macroexpand-1 may give more insight in how case works exactly. I was going to leave this as an exercise to the reader, but thought better of it. :-) Here's an example (formatting added by me):

#;1> (macroexpand-1 '(case a ((x y z) 5) (else 4)))
(let ((g2 a))
  (if (or (eqv? g2 (quote x))
          (eqv? g2 (quote y))
          (eqv? g2 (quote z)))
      (begin 5)
      (begin 4)))