<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML><HEAD> <META http-equiv=Content-Type content="text/html; charset=iso-8859-1"> <META content="MSHTML 6.00.6000.16674" name=GENERATOR> <STYLE></STYLE> </HEAD> <BODY bgColor=#ffffff> <DIV><FONT face="Courier New" size=2>I am not aware to have contributed anything to <A href="http://docs.plt-scheme.org/reference/stx-patterns.html#(form._((lib._scheme/private/stxcase-scheme..ss)._......))"><FONT face="Times New Roman" size=3>http://docs.plt-scheme.org/reference/stx-patterns.html#(form._((lib._scheme/private/stxcase-scheme..ss)._......))</FONT></A>  :)</FONT></DIV> <DIV><FONT face="Courier New" size=2>Wildcards in a pattern are useful though, I think. It is as though saying "i dont care what it is and dont want to know what it is". But if you realy don't care, there is no issue by binding the wild-card. It is possible to do without the wild-card. There are two things that make the wild-card different:</FONT></DIV> <DIV><FONT face="Courier New" size=2>1 : it may appear more than once in a pattern. Other symbols in a pattern do not have this privilege.</FONT></DIV> <DIV><FONT face="Courier New" size=2>2 : The wild-card is completely ignored.</FONT></DIV> <DIV><FONT face="Courier New" size=2>Wild cards are a method in pattern matching (thats what syntax-rules and syntax-case are about)</FONT></DIV> <DIV><FONT face="Courier New" size=2>I must admit that I use the _ only as in (syntax-case stx () ((_ whatever ...) template))</FONT></DIV> <DIV><FONT face="Courier New" size=2>I admit that in most cases a macro writer is interested in what the user did write in the macro call.</FONT></DIV> <DIV><FONT face="Courier New" size=2>I cannot answer the "why". But the "how" is clear to you now, I am sure.</FONT></DIV> <DIV><FONT face="Courier New" size=2>I have done many courses on how to use a computer (dating from decades from now) Students often asked me "why do I have this to do in this way?" Answer: because that is the way that makes it work. On the PLT list or bug-report form you have the opportunity to express how you want to work things (which a few decades ago was unthinkable) My experience is that the PLT team is susceptible for new ideas. But in the present case I think that the wild-card is a commonly accepted and wanted feature that is not going to be altered.</FONT></DIV> <DIV><FONT face="Courier New" size=2></FONT> </DIV> <DIV><FONT face="Courier New" size=2>May be you are experiencing, just as I do, that improvements on the language require efforts of the user on adapting his/her code. That's annoying of course, but without a posotive attitude of the users, software providers cannot implement improvements.</FONT></DIV> <DIV><FONT face="Courier New" size=2></FONT> </DIV> <DIV><FONT face="Courier New" size=2>MHO, Jos</FONT></DIV> <DIV><FONT face="Courier New" size=2><BR> </DIV></FONT> <BLOCKQUOTE style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px"> <DIV style="FONT: 10pt arial">----- Original Message ----- </DIV> <DIV style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B> <A title=yinso.chen@gmail.com href="mailto:yinso.chen@gmail.com">YC</A> </DIV> <DIV style="FONT: 10pt arial"><B>To:</B> <A title=jos.koot@telefonica.net href="mailto:jos.koot@telefonica.net">Jos Koot</A> </DIV> <DIV style="FONT: 10pt arial"><B>Cc:</B> <A title=plt-scheme@list.cs.brown.edu href="mailto:plt-scheme@list.cs.brown.edu">pltscheme</A> </DIV> <DIV style="FONT: 10pt arial"><B>Sent:</B> Tuesday, June 24, 2008 4:04 AM</DIV> <DIV style="FONT: 10pt arial"><B>Subject:</B> Re: [plt-scheme] (v4) wildcard not allowed in expression</DIV> <DIV><BR></DIV>Thanks Jos for the explanation.<BR><BR>I do not grok how prohibiting a wildcard appearing in a template makes it useful.  Is there a place that explains the rationale behind the change?  I tried searching the docs but are not successful so far except for a short description of what you've said in <A href="http://docs.plt-scheme.org/reference/stx-patterns.html#(form._((lib._scheme/private/stxcase-scheme..ss)._......))">http://docs.plt-scheme.org/reference/stx-patterns.html#(form._((lib._scheme/private/stxcase-scheme..ss)._......))</A><BR><BR>Thanks,<BR>yc<BR><BR> <DIV class=gmail_quote>On Mon, Jun 23, 2008 at 6:47 PM, Jos Koot <<A href="mailto:jos.koot@telefonica.net">jos.koot@telefonica.net</A>> wrote:<BR> <BLOCKQUOTE class=gmail_quote style="PADDING-LEFT: 1ex; MARGIN: 0pt 0pt 0pt 0.8ex; BORDER-LEFT: rgb(204,204,204) 1px solid"> <DIV bgcolor="#ffffff"> <DIV><FONT face="Courier New" size=2>Correct. _ has become a wild-card that is bound to a syntax that does not want to be called. You can no longer use _ like other symbols. Hence the wild card may appear in a pattern, but you should not use it in a template. That is in R6RS or PLT 4. In 371 _ was just a symbol like any other one. Why in Pretty Big it still works as an ordinary symbol in old fashion, I don't know.</FONT></DIV> <DIV><FONT face="Courier New" size=2>If you want a symbol that is associated with the name of the syntax use anything else than a wild-card. The wild-card is not bound to a pattern element (except may be in Pretty Big, I don't know)</FONT></DIV> <DIV><FONT face="Courier New" size=2>Jos</FONT></DIV></DIV></BLOCKQUOTE></DIV><BR></BLOCKQUOTE></BODY></HTML>