<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML><HEAD> <META content="text/html; charset=us-ascii" http-equiv=Content-Type> <META name=GENERATOR content="MSHTML 8.00.7600.16588"></HEAD> <BODY> <DIV dir=ltr align=left><SPAN class=863440819-08082010><FONT color=#0000ff size=2 face=Arial>May be we can help better with a reference to the exercise.</FONT></SPAN></DIV> <DIV dir=ltr align=left><SPAN class=863440819-08082010><FONT color=#0000ff size=2 face=Arial>I really can't make up what you are trying to do.</FONT></SPAN></DIV> <DIV dir=ltr align=left><SPAN class=863440819-08082010><FONT color=#0000ff size=2 face=Arial>Jos</FONT></SPAN></DIV><BR> <BLOCKQUOTE style="BORDER-LEFT: #0000ff 2px solid; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px" dir=ltr> <DIV dir=ltr lang=en-us class=OutlookMessageHeader align=left> <HR tabIndex=-1> <FONT size=2 face=Tahoma><B>From:</B> users-bounces@racket-lang.org [mailto:users-bounces@racket-lang.org] <B>On Behalf Of </B>iam_here@aol.in<BR><B>Sent:</B> 08 August 2010 19:20<BR><B>To:</B> users@racket-lang.org<BR><B>Subject:</B> [racket] message passing<BR></FONT><BR></DIV> <DIV></DIV><FONT color=black size=2 face=arial><SPAN style="FONT-SIZE: small" class=Apple-style-span>Hello schemers</SPAN> <DIV><SPAN style="FONT-SIZE: small" class=Apple-style-span><BR></SPAN></DIV> <DIV><SPAN style="FONT-SIZE: small" class=Apple-style-span>what if I have program of massage passing and I have to return the object when it is defined.</SPAN></DIV> <DIV><SPAN style="FONT-SIZE: small" class=Apple-style-span>example-</SPAN></DIV> <DIV><SPAN style="FONT-SIZE: small" class=Apple-style-span><BR></SPAN></DIV> <DIV><SPAN style="FONT-SIZE: small" class=Apple-style-span><FONT class=Apple-style-span color=#2f4f4f>(define (single-order)</FONT></SPAN></DIV> <DIV><SPAN style="FONT-SIZE: small" class=Apple-style-span><SPAN style="WHITE-SPACE: pre" class=Apple-tab-span><FONT class=Apple-style-span color=#2f4f4f></FONT></SPAN><FONT class=Apple-style-span color=#2f4f4f>(let (</FONT></SPAN></DIV> <DIV><SPAN style="FONT-SIZE: small" class=Apple-style-span><SPAN style="WHITE-SPACE: pre" class=Apple-tab-span><FONT class=Apple-style-span color=#2f4f4f></FONT></SPAN><FONT class=Apple-style-span color=#2f4f4f>(delivery #f)</FONT></SPAN></DIV> <DIV><SPAN style="FONT-SIZE: small" class=Apple-style-span><SPAN style="WHITE-SPACE: pre" class=Apple-tab-span><FONT class=Apple-style-span color=#2f4f4f></FONT></SPAN><FONT class=Apple-style-span color=#2f4f4f>)</FONT></SPAN></DIV> <DIV><SPAN style="FONT-SIZE: small" class=Apple-style-span><SPAN style="WHITE-SPACE: pre" class=Apple-tab-span><FONT class=Apple-style-span color=#2f4f4f></FONT></SPAN><FONT class=Apple-style-span color=#2f4f4f>(define (the-order req)</FONT></SPAN></DIV> <DIV><SPAN style="FONT-SIZE: small" class=Apple-style-span><SPAN style="WHITE-SPACE: pre" class=Apple-tab-span><FONT class=Apple-style-span color=#2f4f4f></FONT></SPAN><FONT class=Apple-style-span color=#2f4f4f>(cond ((eq? req 'available)  available)</FONT></SPAN></DIV> <DIV><SPAN style="FONT-SIZE: small" class=Apple-style-span><SPAN style="WHITE-SPACE: pre" class=Apple-tab-span><FONT class=Apple-style-span color=#2f4f4f></FONT></SPAN></SPAN><SPAN style="FONT-FAMILY: monospace; WHITE-SPACE: pre-wrap; FONT-SIZE: medium" class=Apple-style-span><FONT class=Apple-style-span color=#2f4f4f>(</FONT></SPAN><SPAN style="WHITE-SPACE: pre-wrap" class=Apple-style-span><FONT class=Apple-style-span face="Arial, Helvetica, sans-serif"><SPAN style="FONT-SIZE: small" class=Apple-style-span><FONT class=Apple-style-span color=#2f4f4f>else</FONT></SPAN></FONT></SPAN><SPAN style="FONT-FAMILY: monospace; WHITE-SPACE: pre-wrap; FONT-SIZE: medium" class=Apple-style-span><FONT class=Apple-style-span color=#2f4f4f> (</FONT></SPAN><SPAN style="WHITE-SPACE: pre-wrap" class=Apple-style-span><FONT class=Apple-style-span face="Arial, Helvetica, sans-serif"><SPAN style="FONT-SIZE: small" class=Apple-style-span><FONT class=Apple-style-span color=#2f4f4f>error</FONT></SPAN></FONT></SPAN><SPAN style="FONT-FAMILY: monospace; WHITE-SPACE: pre-wrap; FONT-SIZE: medium" class=Apple-style-span><FONT class=Apple-style-span color=#2f4f4f> "</FONT></SPAN><SPAN style="WHITE-SPACE: pre-wrap" class=Apple-style-span><FONT class=Apple-style-span face="Arial, Helvetica, sans-serif"><SPAN style="FONT-SIZE: small" class=Apple-style-span><FONT class=Apple-style-span color=#2f4f4f>the-order</FONT></SPAN></FONT></SPAN><SPAN style="FONT-FAMILY: monospace; WHITE-SPACE: pre-wrap; FONT-SIZE: medium" class=Apple-style-span><FONT class=Apple-style-span color=#2f4f4f>: unknown </FONT></SPAN><SPAN style="WHITE-SPACE: pre-wrap" class=Apple-style-span><FONT class=Apple-style-span face="Arial, Helvetica, sans-serif"><SPAN style="FONT-SIZE: small" class=Apple-style-span><FONT class=Apple-style-span color=#2f4f4f>req</FONT></SPAN></FONT></SPAN><SPAN style="FONT-FAMILY: monospace; WHITE-SPACE: pre-wrap; FONT-SIZE: medium" class=Apple-style-span><FONT class=Apple-style-span color=#2f4f4f>: " </FONT></SPAN><SPAN style="WHITE-SPACE: pre-wrap" class=Apple-style-span><FONT class=Apple-style-span face="Arial, Helvetica, sans-serif"><SPAN style="FONT-SIZE: small" class=Apple-style-span><FONT class=Apple-style-span color=#2f4f4f>req</FONT></SPAN></FONT></SPAN><SPAN style="FONT-FAMILY: monospace; WHITE-SPACE: pre-wrap; FONT-SIZE: medium" class=Apple-style-span><FONT class=Apple-style-span color=#2f4f4f>))</FONT></SPAN></DIV> <DIV><FONT class=Apple-style-span color=#2f4f4f><SPAN style="WHITE-SPACE: pre-wrap; FONT-SIZE: medium" class=Apple-style-span></SPAN></FONT><SPAN style="FONT-SIZE: small" class=Apple-style-span><SPAN style="WHITE-SPACE: pre" class=Apple-tab-span><FONT class=Apple-style-span face="Arial, Helvetica, sans-serif"><FONT class=Apple-style-span color=#2f4f4f>)</FONT></FONT></SPAN></SPAN></DIV> <DIV><SPAN style="FONT-SIZE: small" class=Apple-style-span><SPAN style="WHITE-SPACE: pre" class=Apple-tab-span><FONT class=Apple-style-span color=#2f4f4f><FONT class=Apple-style-span face="Arial, Helvetica, sans-serif"></FONT></FONT></SPAN><FONT class=Apple-style-span color=#2f4f4f>)</FONT></SPAN></DIV> <DIV><SPAN style="FONT-SIZE: small" class=Apple-style-span><FONT class=Apple-style-span color=#2f4f4f><BR></FONT></SPAN></DIV> <DIV><SPAN style="FONT-SIZE: small" class=Apple-style-span><FONT class=Apple-style-span color=#2f4f4f>(define (available)</FONT></SPAN></DIV> <DIV><SPAN style="FONT-SIZE: small" class=Apple-style-span><SPAN style="WHITE-SPACE: pre" class=Apple-tab-span><FONT class=Apple-style-span color=#2f4f4f></FONT></SPAN><FONT class=Apple-style-span color=#2f4f4f>(set! delivery #t))</FONT></SPAN></DIV> <DIV><SPAN style="FONT-SIZE: small" class=Apple-style-span><FONT class=Apple-style-span color=#2f4f4f><BR></FONT></SPAN></DIV> <DIV><SPAN style="FONT-SIZE: small" class=Apple-style-span><FONT class=Apple-style-span color=#2f4f4f>the-order</FONT></SPAN></DIV> <DIV><SPAN style="FONT-SIZE: small" class=Apple-style-span><SPAN style="WHITE-SPACE: pre" class=Apple-tab-span><FONT class=Apple-style-span color=#2f4f4f></FONT></SPAN><FONT class=Apple-style-span color=#2f4f4f>)</FONT></SPAN></DIV> <DIV><SPAN style="FONT-SIZE: small" class=Apple-style-span><FONT class=Apple-style-span color=#2f4f4f>   )</FONT></SPAN></DIV> <DIV><SPAN style="FONT-SIZE: small" class=Apple-style-span><FONT class=Apple-style-span color=#2f4f4f><BR></FONT></SPAN></DIV> <DIV><SPAN style="FONT-SIZE: small" class=Apple-style-span><FONT class=Apple-style-span color=#2f4f4f>(define (available object)</FONT></SPAN></DIV> <DIV><SPAN style="FONT-SIZE: small" class=Apple-style-span><SPAN style="WHITE-SPACE: pre" class=Apple-tab-span><FONT class=Apple-style-span color=#2f4f4f></FONT></SPAN><FONT class=Apple-style-span color=#2f4f4f>((object 'available)))</FONT></SPAN></DIV> <DIV><SPAN style="FONT-SIZE: small" class=Apple-style-span><BR></SPAN></DIV> <DIV><SPAN style="FONT-SIZE: small" class=Apple-style-span><BR></SPAN></DIV> <DIV><SPAN style="FONT-SIZE: small" class=Apple-style-span>=> now when I will run it like</SPAN></DIV> <DIV><SPAN style="FONT-SIZE: small" class=Apple-style-span><BR></SPAN></DIV> <DIV><SPAN style="FONT-SIZE: small" class=Apple-style-span><FONT class=Apple-style-span color=#2f4f4f>(define mcdon(single-order))</FONT></SPAN></DIV> <DIV><SPAN style="FONT-SIZE: small" class=Apple-style-span><BR></SPAN></DIV> <DIV><SPAN style="FONT-SIZE: small" class=Apple-style-span>- it should return mcdon instead of <#unspecified></SPAN></DIV> <DIV><SPAN style="FONT-SIZE: small" class=Apple-style-span><BR></SPAN></DIV> <DIV><SPAN style="FONT-SIZE: small" class=Apple-style-span>Any ideas?? </SPAN></DIV> <DIV><SPAN style="FONT-SIZE: small" class=Apple-style-span><SPAN style="WHITE-SPACE: pre" class=Apple-tab-span></SPAN><BR></SPAN><BR> <DIV style="CLEAR: both"></DIV></DIV></BLOCKQUOTE></FONT></BODY></HTML>