20 lines
575 B
Racket
20 lines
575 B
Racket
#lang typed/racket/base
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(provide list-union list-difference)
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(: list-union ((Listof Symbol) (Listof Symbol) -> (Listof Symbol)))
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(define (list-union s1 s2)
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(cond [(null? s1) s2]
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[(memq (car s1) s2)
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(list-union (cdr s1) s2)]
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[else (cons (car s1) (list-union (cdr s1) s2))]))
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(: list-difference ((Listof Symbol) (Listof Symbol) -> (Listof Symbol)))
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(define (list-difference s1 s2)
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(cond [(null? s1) '()]
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[(memq (car s1) s2)
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(list-difference (cdr s1) s2)]
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[else
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(cons (car s1) (list-difference (cdr s1) s2))])) |