30 lines
748 B
Racket
30 lines
748 B
Racket
#lang typed/syndicate/roles
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(require rackunit/turnstile)
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(define (∀ (X) (poly-cons [x : X]
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[xs : (List X)]
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-> (List X)))
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(cons x xs))
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(define int-list : (List Int) (list 1 2 3))
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(check-type (poly-cons 0 int-list)
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: (List Int)
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-> (list 0 1 2 3))
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(define string-list : (List String) (list "group" "of" "helpful" "badgers"))
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(check-type (poly-cons "a" string-list)
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: (List String)
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-> (list "a" "group" "of" "helpful" "badgers"))
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(typecheck-fail (poly-cons "hello" int-list))
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(define string-int-list : (List (U String Int))
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(list "hi" 42 "badgers"))
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;; shouldn't mess about with unions
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(typecheck-fail (poly-cons "go" string-int-list))
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