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;"soundex.scm" Original SOUNDEX algorithm.
;From jjb@isye.gatech.edu Mon May 2 22:29:43 1994
;
; This code is in the public domain.
; Taken from Knuth, Vol. 3 "Sorting and searching", pp 391--2
;;; 2003-01-26 L.J. Buitinck converted to use dotted pairs for codes.
(require 'common-list-functions)
;@
(define SOUNDEX
(let* ((letters-to-omit
'(#\A #\E #\H #\I #\O #\U #\W #\Y))
(codes
'((#\B . #\1)
(#\F . #\1)
(#\P . #\1)
(#\V . #\1)
;;
(#\C . #\2)
(#\G . #\2)
(#\J . #\2)
(#\K . #\2)
(#\Q . #\2)
(#\S . #\2)
(#\X . #\2)
(#\Z . #\2)
;;
(#\D . #\3)
(#\T . #\3)
;;
(#\L . #\4)
;;
(#\M . #\5)
(#\N . #\5)
;;
(#\R . #\6)))
(xform
(lambda (c)
(let ((code (assv c codes)))
(if code
(cdr code)
c)))))
(lambda (name)
(let ((char-list
(map char-upcase
(remove-if (lambda (c)
(not (char-alphabetic? c)))
(string->list name)))))
(if (null? char-list)
name
(let* ( ;; Replace letters except first with codes:
(n1 (cons (car char-list) (map xform char-list)))
;; If 2 or more letter with same code are adjacent
;; in the original name, omit all but the first:
(n2 (let loop ((chars n1))
(cond ((null? (cdr chars))
chars)
(else
(if (char=? (xform (car chars))
(cadr chars))
(loop (cdr chars))
(cons (car chars) (loop (cdr chars))))))))
;; Omit vowels and similar letters, except first:
(n3 (cons (car char-list)
(remove-if
(lambda (c)
(memv c letters-to-omit))
(cdr n2)))))
;;
;; pad with 0's or drop rightmost digits until of form "annn":
(let loop ((rev-chars (reverse n3)))
(let ((len (length rev-chars)))
(cond ((= 4 len)
(list->string (reverse rev-chars)))
((> 4 len)
(loop (cons #\0 rev-chars)))
((< 4 len)
(loop (cdr rev-chars))))))))))))
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