;"soundex.scm" Original SOUNDEX algorithm. ;From jjb@isye.gatech.edu Mon May 2 22:29:43 1994 ; ; This code is in the public domain. ;Date: Mon, 2 May 94 13:45:39 -0500 ; Taken from Knuth, Vol. 3 "Sorting and searching", pp 391--2 (require 'common-list-functions) (define SOUNDEX (let* ((letters-to-omit (list #\A #\E #\H #\I #\O #\U #\W #\Y)) (codes (list (list #\B #\1) (list #\F #\1) (list #\P #\1) (list #\V #\1) ; (list #\C #\2) (list #\G #\2) (list #\J #\2) (list #\K #\2) (list #\Q #\2) (list #\S #\2) (list #\X #\2) (list #\Z #\2) ; (list #\D #\3) (list #\T #\3) ; (list #\L #\4) ; (list #\M #\5) (list #\N #\5) ; (list #\R #\6))) (xform (lambda (c) (let ((code (assq c codes))) (if code (cadr 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) (memq 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))))))))))))