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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.
+
+;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))))))))))))
+
+