<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML><HEAD><TITLE></TITLE> <META content="text/html; charset=us-ascii" http-equiv=Content-Type> <META name=GENERATOR content="MSHTML 8.00.7600.16588"></HEAD> <BODY bgColor=#ffffff text=#000000> <DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN class=481380623-18072010>I am not sure it is a good idea to add many almost-synonyms in a language. I just was a little bit curious. The change is backward compatible and I have no objections against it.</SPAN></FONT></DIV> <DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN class=481380623-18072010>Indeed values to be inserted for missing keys often are #f or 0 or '( ). It types nicely not having to wrap these basic constants in a thunk and to gain efficiency for free. You only have to be aware of the fact that if the value to be inserted is to be or might be a procedure, such as (lambda (x) x) as the most elementary procedure when building a hash of procedures, you have to wrap it as (lambda ( ) (lambda (x) x)). Because the latter does not capture any variables, it may even be optimized such as to avoid multiple construction of the identity function.</SPAN></FONT></DIV> <DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN class=481380623-18072010>In this case I would write or have my macro or module expand to for example:</SPAN></FONT></DIV> <DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN class=481380623-18072010></SPAN></FONT> </DIV> <DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN class=481380623-18072010>(define (identity x) x)</SPAN></FONT></DIV> <DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN class=481380623-18072010>(define (default) identity)</SPAN></FONT></DIV> <DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN class=481380623-18072010></SPAN></FONT> </DIV> <DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN class=481380623-18072010>(let loop ((...))</SPAN></FONT></DIV> <DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN class=481380623-18072010> ...</SPAN></FONT></DIV> <DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN class=481380623-18072010> (hash-ref! hash key default)</SPAN></FONT></DIV> <DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN class=481380623-18072010> ...)</SPAN></FONT></DIV> <DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN class=481380623-18072010></SPAN></FONT> </DIV> <DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN class=481380623-18072010>I am pretty sure that in this case the identity function is constructed once only.</SPAN></FONT></DIV> <DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN class=481380623-18072010>Jos</SPAN></FONT></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> Neil Van Dyke [mailto:neil@neilvandyke.org] <BR><B>Sent:</B> 19 July 2010 00:22<BR><B>To:</B> Jos Koot<BR><B>Cc:</B> 'plt-scheme'<BR><B>Subject:</B> Re: [racket] hash-ref<BR></FONT><BR></DIV> <DIV></DIV>Jos Koot wrote at 07/18/2010 09:26 AM: <BLOCKQUOTE cite=mid:04AD96DBB28646C7819414ACAF25F51D@JacobPC type="cite"> <META name=GENERATOR content="MSHTML 8.00.7600.16588"> <DIV><FONT size=2 face="Courier New"><SPAN class=132071113-18072010>(hash-ref a-hash a-key a-value)</SPAN></FONT></DIV> <DIV><FONT size=2 face="Courier New"><SPAN class=132071113-18072010>In the past a-value was required to be a procedure.</SPAN></FONT></DIV> <DIV><FONT size=2 face="Courier New"><SPAN class=132071113-18072010>Now it can be anything.</SPAN></FONT></DIV></BLOCKQUOTE>[...]<BR> <BLOCKQUOTE cite=mid:04AD96DBB28646C7819414ACAF25F51D@JacobPC type="cite"> <DIV><FONT size=2 face="Courier New"><SPAN class=132071113-18072010><SPAN class=132071113-18072010></SPAN></SPAN></FONT> </DIV> <DIV><FONT size=2 face="Courier New"><SPAN class=132071113-18072010><SPAN class=132071113-18072010>In short, I do not well understand the reason to relax the contract of hash-ref and hash-ref!.</SPAN></SPAN></FONT></DIV></BLOCKQUOTE><BR>This behavior seems a little on the uncomfortable side of automagical to me, and -- although I can understand the desire to keep the short name -- I would've preferred separate procedures for the default-thunk and default-value variations.<BR><BR>Perhaps the short-name procedure could be the automagical one, and there could be longer-name procedures, like "hash-ref/default-thunk" and "hash-ref/default-value", for people who prefer a little less automagic in that regard.<BR><BR> <DIV class=moz-signature>-- <BR><A class=moz-txt-link-freetext href="http://www.neilvandyke.org/">http://www.neilvandyke.org/</A> </DIV></BLOCKQUOTE></BODY></HTML>