From: Ramakrishnan Muthukrishnan <vu3rdd@gmail.com>
Date: Sun, 24 Apr 2011 10:25:01 +0000 (+0530)
Subject: solution to 3.38
X-Git-Url: https://git.rkrishnan.org/about.html?a=commitdiff_plain;h=9ddee199c3c2dd6c4ac5cf9af4e16cc3d4c1cf25;p=sicp.git

solution to 3.38
---

diff --git a/src/sicp/ex3_38.rkt b/src/sicp/ex3_38.rkt
new file mode 100644
index 0000000..7481849
--- /dev/null
+++ b/src/sicp/ex3_38.rkt
@@ -0,0 +1,69 @@
+#lang racket
+
+#|
+
+Peter: 	(set! balance (+ balance 10))
+Paul: 	(set! balance (- balance 20))
+Mary: 	(set! balance (- balance (/ balance 2)))
+
+1.
+
+a. Peter deposits $10
+b. Paul withdraws $20
+c. Mary withdraws half of balance.
+
+100 + 10 - 20 = 90 -> 90/2 -> $45
+
+2. 
+
+a. Peter deposits $10
+b. Mary withdraws half of balance.
+c. Paul withdraws $20
+
+100 + 10 -> 55 - 20 -> $35
+
+3.
+
+a. Paul withdraws $20
+b. Peter deposits $10
+c. Mary withdraws half of balance.
+
+100 - 20 + 10 -> 110 /2 -> $55
+
+4. 
+
+a. Paul withdraws $20
+b. Mary withdraws half of balance.
+c. Peter deposits $10
+
+100 - 20 => 80 / 2 => 40 + 10 => 50
+
+5.
+
+a. Mary withdraws half of balance.
+b. Peter deposits $10
+c. Paul withdraws $20
+
+100 / 2 => 50 + 10 - 20 => 40
+
+6.
+
+a. Mary withdraws half of balance.
+b. Paul withdraws $20
+c. Peter deposits $10
+
+100 / 2 => 50 - 20 + 10 => 40
+
+|#
+
+#|
+
+Balance could take many values if the three transactions are allowed to
+happen concurrently.
+
+It could be 110, 80 or 50 if one of them mutates the balance variable
+at the end depending on which one manages to finish last. It could also
+be that 2 of them work concurrently and the resultant value is processed
+by the third transaction.
+
+|#
\ No newline at end of file