71 lines
1.9 KiB
Racket
71 lines
1.9 KiB
Racket
#lang typed/syndicate/roles
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(require rackunit/turnstile)
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(check-type (for/fold ([x 0])
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([y (list 1 2 3)])
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x)
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: Int
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⇒ 0)
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(check-type (for/fold ([x 0])
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([y (list 1 2 3)])
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y)
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: Int
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⇒ 3)
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(define-type-alias Inventory (List (Tuple String Int)))
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(define inventory0 (list (tuple "The Wind in the Willows" 5)
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(tuple "Catch 22" 2)
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(tuple "Candide" 33)))
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(check-type (for/fold ([stock 0])
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([item inventory0])
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(select 1 item))
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: Int
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⇒ 33)
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(check-type (for/fold ([stock 0])
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([item inventory0])
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(if (equal? "Catch 22" (select 0 item))
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(select 1 item)
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stock))
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: Int
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⇒ 2)
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(define (lookup [title : String]
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[inv : Inventory] -> Int)
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(for/fold ([stock 0])
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([item inv])
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(if (equal? title (select 0 item))
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(select 1 item)
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stock)))
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(check-type lookup : (→fn String Inventory Int))
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(define (zip [xs : (List Int)]
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[ys : (List Int)])
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((inst reverse (Tuple Int Int))
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(for/fold ([acc : (List (Tuple Int Int))
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(list)])
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([x xs]
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[y ys])
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(cons (tuple x y) acc))))
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(check-type (zip (list 1 2 3) (list 4 5 6))
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: (List (Tuple Int Int))
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⇒ (list (tuple 1 4) (tuple 2 5) (tuple 3 6)))
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;; binding in #:when isn't handled
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#;(define (zip-even [xs : (List Int)]
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[ys : (List Int)])
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((inst reverse (Tuple Int Int))
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(for/fold ([acc : (List (Tuple Int Int))
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(list)])
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([x xs]
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#:when (even? x)
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[y ys]
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#:when (even? y))
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(cons (tuple x y) acc))))
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