Restricting the keywords

static-checking.rkt

#lang typed/racket

(: f (case->       
      (Integer [#:application Integer] [#:context Nothing] -> (List Integer Integer))
      (Integer [#:context Integer] [#:application Nothing] -> (List Integer Integer))))
(define (f x #:application [a 0] #:context [c 0])
  (list a c))

(f 1)
(f 1 #:application 5)
(f 1 #:context 5)
(f 1 #:application 5 #:context 5) ;; doesn't typecheck

too-many-keywords.rkt

#lang typed/racket

(: f (Integer [#:application Integer]  [#:context Integer]
              -> (List Integer Integer)))
(define (f x #:application [#{a : (U Integer #f)} #f] #:context [#{c : (U Integer #f)} #f])
  (cond [(and a c) (error "too many keywords")]
        [a (list a 0)]
        [c (list 0 c)]
        [else (list 0 0)]))