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readme.rkt (545B)

      1 #lang typed/racket
      2 (require type-expander
      3          typed/rackunit
      4          (for-syntax racket/list))
      5 
      6 (define-type-expander (Repeat stx)
      7   (syntax-case stx ()
      8     [(_ t n)
      9      #`(List #,@(map (λ (x) #'t)
     10                      (range (syntax->datum #'n))))]))
     11 
     12 (: five-strings (→ String (Repeat String 5)))
     13 (define (five-strings x)
     14   (list x "a" "b" "c" "d"))
     15 
     16 (check-equal? (five-strings "hello")
     17               '("hello" "a" "b" "c" "d"))
     18 
     19 (check-equal? (ann (five-strings "moon") (Repeat String 5))
     20               '("moon"  "a" "b" "c" "d"))