# [plt-scheme] for comprehensions in typed-scheme

On Mon, Jun 8, 2009 at 1:45 PM, Sam TH<samth at ccs.neu.edu> wrote:
>* This works:
*
Groovy.
Next dumb question:
(define-struct: Mark ())
(define-struct: (Dot Mark) ([x : Number] [y : Number]))
(: bounding-box ((Listof Dot) -> Box))
(define (bounding-box marks)
;; This only works for Dots. It should work for all Marks
(define: xs : (Listof Number) (map Dot-x marks))
(define: ys : (Listof Number) (map Dot-y marks))
(define: max-x : Number (#{apply @ Number Number} max xs))
(define: max-y : Number (apply max ys))
(define: min-x : Number (apply min xs))
(define: min-y : Number (apply min ys))
...
)
All the calls to apply fail with
typecheck: Bad arguments to function in apply:
Domain: Number Number *
Arguments: (Listof Number) *
I don't get it! At the REPL I can do:
(apply max (list 1 2 3 4))
and it works. My expressions above seem equivalent. What must I do to
get this past the type checker?
N.