<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML><HEAD> <META http-equiv=Content-Type content="text/html; charset=utf-8"> <META content="MSHTML 6.00.6000.16890" name=GENERATOR> <STYLE></STYLE> </HEAD> <BODY bgColor=#ffffff> <DIV><FONT face="Courier New" size=2>You mean the following?</FONT></DIV> <DIV><FONT face="Courier New" size=2></FONT> </DIV> <DIV><FONT face="Courier New" size=2>#lang scheme</FONT></DIV> <DIV><FONT face="Courier New" size=2>(define-syntax (my-hash stx)<BR> (syntax-case stx ()<BR>  ((_ (key . val) ...)<BR>   (let<BR>    ((keys (map syntax->datum (syntax->list #'(key ...))))<BR>     (vals (map syntax->datum (syntax->list #'(val ...)))))</FONT></DIV> <DIV><FONT face="Courier New" size=2>    ; make the hash-table at expansion time!<BR>    (datum->syntax #'here (make-immutable-hash (map cons keys vals)))))))</FONT></DIV> <DIV><FONT face="Courier New" size=2></FONT> </DIV> <DIV><FONT face="Courier New" size=2>; tests:</FONT></DIV> <DIV><FONT face="Courier New" size=2>(define h (my-hash (a . 1) (b . 2) (c . 3)))<BR>(hash-map h list) ; --> ((a 1) (b 2) (c 3))<BR>(hash-ref h 'a) ; 1</FONT></DIV> <DIV><FONT face="Courier New" size=2></FONT> </DIV> <DIV><FONT face="Courier New" size=2>Best wishes, Jos.</FONT></DIV> <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=psteiger@dcc.ufba.br href="mailto:psteiger@dcc.ufba.br">Patrick Steiger</A> </DIV> <DIV style="FONT: 10pt arial"><B>To:</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: 10pt arial"><B>Sent:</B> Monday, September 14, 2009 5:39 AM</DIV> <DIV style="FONT: 10pt arial"><B>Subject:</B> [plt-scheme] Define-syntax and #hash - ugly compiling behavior</DIV> <DIV><BR></DIV>Hello, all. This is my first post on the list, I'm a CS student and I've been giving Scheme a shot. (liking it a lot, so far).<BR><BR>Now, given the following code:<BR><BR>(define-syntax myhash<BR>  (syntax-rules (->)<BR>    [(_ (x -> y) ...)<BR>     #hash((x . y) ...)]))<BR><BR>When trying to compile it, I get:<BR><BR>. read: expected `(' or `[' or `{' to start a hash pair<BR clear=all><BR>I was told that this happens because the compiler recognizes #hash as a hash-table long before (in the lexical analysis?) knowing that it is inside a (define-syntax), and therefore doesn't get the semantics of '...' - it just interprets it as illegal syntax.<BR><BR>This seems like a major wart with the language. What are your opinions?<BR><BR>-- <BR>Patrick Steiger.<BR><BR>"Theory is when you know something, but it doesn't work. Practice is<BR>when something works, but you don't know why.<BR>Programmers combine theory and practice: Nothing works and they don't<BR>know why." - Anon <BR> <P> <HR> <P></P>_________________________________________________<BR>  For list-related administrative tasks:<BR>  http://list.cs.brown.edu/mailman/listinfo/plt-scheme<BR></BLOCKQUOTE></BODY></HTML>