38 lines
1 KiB
Racket
38 lines
1 KiB
Racket
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#lang racket
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(require srfi/14)
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(define 0-char (char->integer #\0))
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(define A-char (char->integer #\A))
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(define (cusip-value c)
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(cond
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[(char-set-contains? char-set:digit c)
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(- (char->integer c) 0-char)]
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[(char-set-contains? char-set:upper-case c)
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(+ 10 (- (char->integer c) A-char))]
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[(char=? c #\*) 36]
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[(char=? c #\@) 37]
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[(char=? c #\#) 38]))
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(define (cusip-check-digit cusip)
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(modulo
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(- 10
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(modulo
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(for/sum
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((i (sequence-map add1 (in-range 8))) (c (in-string cusip)))
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(let* ((v (cusip-value c)) (v′ (if (even? i) (* v 2) v)))
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(+ (quotient v′ 10) (modulo v′ 10)))) 10)) 10))
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(define (CUSIP? s)
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(char=? (string-ref s (sub1 (string-length s)))
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(integer->char (+ 0-char (cusip-check-digit s)))))
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(module+ test
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(require rackunit)
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(check-true (CUSIP? "037833100"))
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(check-true (CUSIP? "17275R102"))
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(check-true (CUSIP? "38259P508"))
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(check-true (CUSIP? "594918104"))
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(check-false (CUSIP? "68389X106"))
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(check-true (CUSIP? "68389X105")))
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