<html> <head> <style></style> </head> <body class='hmmessage'> Thanks very much. This has put me in the right direction!<br><br><hr id="stopSpelling">From: jos.koot@telefonica.net<br>To: johnyseventy@hotmail.com; noelwelsh@gmail.com<br>CC: plt-scheme@list.cs.brown.edu<br>Subject: Re: [plt-scheme] Very basic macro question<br>Date: Tue, 19 Jan 2010 19:42:27 +0100<br><br> <style> .ExternalClass .ecxhmmessage P {padding-bottom:0px;padding-left:0px;padding-right:0px;padding-top:0px;} .ExternalClass BODY.ecxhmmessage {font-family:Verdana;font-size:10pt;} </style> <div><font face="Courier New">You probably want match. Alernatively you can use syntax-case in a procedure for example:</font></div> <div><font face="Courier New"></font> </div> <div><font face="Courier New">#lang scheme<br>(define (trafo x)<br> (syntax->datum<br>  (syntax-case x ()<br>   (id (identifier? #'id) #'(identifier id))<br>   ((a ...) #'(list a ...))<br>   (else #'else))))</font></div> <div> </div> <div><font face="Courier New">(trafo 'a) ; --> (identifier a)<br>(trafo '(a b c)) ; (list a b c)<br>(trafo "string") ; --> string</font></div> <div><font face="Courier New"></font> </div> <div><font face="Courier New">Jos</font></div> <blockquote style="border-left: 2px solid rgb(0, 0, 0); padding-left: 5px; padding-right: 0px; margin-left: 5px; margin-right: 0px;"> <div style="font-family: arial; font-style: normal; font-variant: normal; font-weight: normal; font-size: 10pt; line-height: normal; font-size-adjust: none; font-stretch: normal; -x-system-font: none;">----- Original Message ----- </div> <div style="background: rgb(228, 228, 228) none repeat scroll 0% 0%; font-family: arial; font-style: normal; font-variant: normal; font-weight: normal; font-size: 10pt; line-height: normal; font-size-adjust: none; font-stretch: normal; -x-system-font: none; -moz-background-clip: border; -moz-background-origin: padding; -moz-background-inline-policy: continuous;"><b>From:</b> <a title="johnyseventy@hotmail.com" href="mailto:johnyseventy@hotmail.com">johny seventy</a> </div> <div style="font-family: arial; font-style: normal; font-variant: normal; font-weight: normal; font-size: 10pt; line-height: normal; font-size-adjust: none; font-stretch: normal; -x-system-font: none;"><b>To:</b> <a title="noelwelsh@gmail.com" href="mailto:noelwelsh@gmail.com">noelwelsh@gmail.com</a> </div> <div style="font-family: arial; font-style: normal; font-variant: normal; font-weight: normal; font-size: 10pt; line-height: normal; font-size-adjust: none; font-stretch: normal; -x-system-font: none;"><b>Cc:</b> <a title="plt-scheme@list.cs.brown.edu" href="mailto:plt-scheme@list.cs.brown.edu">plt-scheme@list.cs.brown.edu</a> </div> <div style="font-family: arial; font-style: normal; font-variant: normal; font-weight: normal; font-size: 10pt; line-height: normal; font-size-adjust: none; font-stretch: normal; -x-system-font: none;"><b>Sent:</b> Tuesday, January 19, 2010 7:26 PM</div> <div style="font-family: arial; font-style: normal; font-variant: normal; font-weight: normal; font-size: 10pt; line-height: normal; font-size-adjust: none; font-stretch: normal; -x-system-font: none;"><b>Subject:</b> RE: [plt-scheme] Very basic macro question</div> <div><br></div>> Date: Sun, 17 Jan 2010 18:42:32 +0000<br>> Subject: Re: [plt-scheme] Very basic macro question<br>> From: <a href="mailto:noelwelsh@gmail.com">noelwelsh@gmail.com</a><br>> To: <a href="mailto:johnyseventy@hotmail.com">johnyseventy@hotmail.com</a><br>> CC: <a href="mailto:plt-scheme@list.cs.brown.edu">plt-scheme@list.cs.brown.edu</a><br>> <br>> On Sun, Jan 17, 2010 at 2:22 PM, johny seventy <<a href="mailto:johnyseventy@hotmail.com">johnyseventy@hotmail.com</a>> wrote:<br>> > I understand why example<br>> > four works but is there anyway I can do this without eval?<br>> <br>> A transformer binding and syntax-local-value.<br>> <br>> It doesn't make sense to parameterise a macro by a run-time value --<br>> macros are expanded before run-time so they cannot depend on run-time<br>> values.<br>> <br>> N.<br><br>Thanks for the responses. I just want to clarify one more thing.<br><br>I have an sexpr which is created dynamically at runtime and I want to transform this sexpr. It seemed really easy to do the transformation using a syntax-rules macro. So the problem is I have missed the boat at this stage as macro expansion has already taken place. The only way I can see how to invoke the macro at this stage is by using eval. I am not sure what you mean by a transformer binding and syntax-local-value. Is there a simple example of this in action I could take a look at?<br><br>Thanks for your patience. <br><br><br><br><br><br> <hr> Not got a Hotmail account? <a href="http://clk.atdmt.com/UKM/go/197222280/direct/01/">Sign-up now - Free</a> <BR><hr> <BR>_________________________________________________<br>  For list-related administrative tasks:<br>  http://list.cs.brown.edu/mailman/listinfo/plt-scheme<br> <BR><hr> <BR><br>Se certificó que el correo entrante no contiene virus.<br>Comprobada por AVG - www.avg.es <br>Versión: 9.0.730 / Base de datos de virus: 270.14.150/2632 - Fecha de la versión: 01/19/10 08:34:00<br></blockquote> <br /><hr />Not got a Hotmail account? <a href='http://clk.atdmt.com/UKM/go/197222280/direct/01/' target='_new'>Sign-up now - Free</a></body> </html>