36 lines
864 B
Racket
36 lines
864 B
Racket
#lang turnstile
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(provide Left
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Right
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Either
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left
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right
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partition/either)
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(require "core-types.rkt")
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(require "core-expressions.rkt")
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(require "for-loops.rkt")
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(require "list.rkt")
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(define-constructor* (left : Left v))
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(define-constructor* (right : Right v))
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(define-type-alias (Either A B)
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(U (Left A)
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(Right B)))
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(define (∀ (X Y Z) (partition/either [xs : (List X)]
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[pred : (→fn X (Either Y Z))]
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-> (Tuple (List Y) (List Z))))
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(for/fold ([lefts (List Y) (list)]
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[rights (List Z) (list)])
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([x xs])
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(define y-or-z (pred x))
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(match y-or-z
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[(left (bind y Y))
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(tuple (cons y lefts)
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rights)]
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[(right (bind z Z))
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(tuple lefts
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(cons z rights))])))
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