Fix implode and explode to handle arbitrary objects and fix the

handling of strings.

diff --git a/v7/src/sicp/compat.scm b/v7/src/sicp/compat.scm
index a575d8f41096ef82cffe807c64075a1b5f129044..3ac86726e6d6f778c52ea6549e644599f851aa33 100644 (file)
--- a/v7/src/sicp/compat.scm
+++ b/v7/src/sicp/compat.scm
@@ -1,6 +1,6 @@
 #| -*-Scheme-*-
 
-$Header: /Users/cph/tmp/foo/mit-scheme/mit-scheme/v7/src/sicp/compat.scm,v 1.3 1991/04/06 06:51:33 jinx Exp $
+$Header: /Users/cph/tmp/foo/mit-scheme/mit-scheme/v7/src/sicp/compat.scm,v 1.4 1991/05/04 21:51:19 jinx Exp $
 
 Copyright (c) 1987, 1988, 1989, 1990 Massachusetts Institute of Technology
 
@@ -93,24 +93,39 @@ MIT in each case. |#
 (define (nthcdr n l)
   (list-tail l n))
 
-(define (explode string)
+(define (object->string object)
+  (cond ((symbol? object) (symbol->string object))
+       ((number? object) (number->string object))
+       ((string? object) (string-append "\"" object "\""))
+       (else
+        (with-output-to-string
+          (lambda ()
+            (write object))))))
+
+(define (string->object object)
+  (with-input-from-string object
+    read))
+
+(define (explode object)
   (map (lambda (character)
         (let ((string (char->string character)))
           (or (string->number string)
               (string->symbol string))))
-       (string->list string)))
+       (string->list
+       (object->string object))))
 
 (define (implode list)
-  (list->string
-   (map (lambda (element)
-         (cond ((digit? element)
-                (string-ref (number->string element) 0))
-               ((singleton-symbol? element)
-                (string-ref (symbol->string element) 0))
-               (else
-                (error "Element neither digit nor singleton symbol"
-                       element))))
-       list)))
+  (string->object
+   (list->string
+    (map (lambda (element)
+          (cond ((digit? element)
+                 (string-ref (number->string element) 0))
+                ((singleton-symbol? element)
+                 (string-ref (symbol->string element) 0))
+                (else
+                 (error "Element neither digit nor singleton symbol"
+                        element))))
+        list))))
 \f
 (define (close-channel port)
   (cond ((input-port? port) (close-input-port port))