From: Ramakrishnan Muthukrishnan <vu3rdd@gmail.com>
Date: Mon, 13 Jun 2011 16:52:13 +0000 (+0530)
Subject: solution to 3.44
X-Git-Url: https://git.rkrishnan.org/%5B/frontends/%22news.html/using.html?a=commitdiff_plain;h=22c9ed85943b0b665c9da80590df64862f812355;p=sicp.git

solution to 3.44
---

diff --git a/src/sicp/ex3_44.rkt b/src/sicp/ex3_44.rkt
new file mode 100644
index 0000000..7484364
--- /dev/null
+++ b/src/sicp/ex3_44.rkt
@@ -0,0 +1,19 @@
+#lang racket
+
+;; Consider the problem of transferring an amount from one account to
+;; another. Ben Bitdiddle claims that this can be accomplished with the
+;; following procedure, even if there are multiple people concurrently 
+;; transferring money among multiple accounts, using any account 
+;; mechanism that serializes deposit and withdrawal transactions, for 
+;; example, the version of make-account in the text above.
+
+(define (transfer from-account to-account amount)
+  ((from-account 'withdraw) amount)
+  ((to-account 'deposit) amount))
+
+#|
+
+Since withdraw and deposit themselves are 'atomic' (or rather 'safe')
+there is no problem with this routine. 
+
+|#
\ No newline at end of file