Data commit

Task/Associative-array-Merging/Scheme/associative-array-merging-1.ss

@@ -0,0 +1,20 @@
+; Merge alists by appending the update list onto the front of the base list.
+; (The extra '() is so that append doesn't co-opt the second list.)
+(define append-alists
+  (lambda (base update)
+    (append update base '())))
+
+; Test...
+(printf "~%Merge using append procedure...~%")
+; The original base and update alists.
+(let ((base '(("name" . "Rocket Skates") ("price" . 12.75) ("color" . "yellow" )))
+      (update '(("price" . 15.25) ("color" . "red") ("year" . 1974))))
+  ; Merge by appending the update list onto the front of the base list.
+  (let ((merged (append-alists base update)))
+    ; Show that everything worked.
+    (printf "Merged alist:~%~s~%" merged)
+    (printf "Values from merged alist:~%")
+    (let loop ((keys '("name" "price" "color" "year")))
+      (unless (null? keys)
+        (printf "~s -> ~s~%" (car keys) (cdr (assoc (car keys) merged)))
+        (loop (cdr keys))))))

Task/Associative-array-Merging/Scheme/associative-array-merging-2.ss

@@ -0,0 +1,27 @@
+; Merge the given alists.  Prefer the items from the "update" alist.
+; Returns a new list; the argument lists are not modified.
+(define merge-alists
+  (lambda (base update)
+    (let ((merged (list-copy update))
+          (remains (list-copy base)))
+      (let loop ((shadowing merged))
+        (if (null? shadowing)
+          (append merged remains)
+          (begin (set! remains (remp (lambda (pair) (equal? (car pair) (caar shadowing)))
+                                     remains))
+                 (loop (cdr shadowing))))))))
+
+; Test...
+(printf "~%Merge using defined merge-alists procedure...~%")
+; The original base and update alists.
+(let ((base '(("name" . "Rocket Skates") ("price" . 12.75) ("color" . "yellow" )))
+      (update '(("price" . 15.25) ("color" . "red") ("year" . 1974))))
+  ; Merge using the defined merge-alists procedure.
+  (let ((merged (merge-alists base update)))
+    ; Show that everything worked.
+    (printf "Merged alist:~%~s~%" merged)
+    (printf "Values from merged alist:~%")
+    (let loop ((keys '("name" "price" "color" "year")))
+      (unless (null? keys)
+        (printf "~s -> ~s~%" (car keys) (cdr (assoc (car keys) merged)))
+        (loop (cdr keys))))))