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Paste # 4119
2015-03-26 11:58:31

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  1. #lang typed/racket
  2.  
  3. (: f (U [Natural -> Integer]
  4.         [Integer -> String]))
  5. (define (f x) "foo")
  6. (f 0)
  7. (f -1)

=>

- : (U Integer String)

"foo"

eval:5:0: Type Checker: type mismatch

  expected: Nonnegative-Integer

  given: Negative-Fixnum

  in: -1