<!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><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> <DIV><FONT size=2 face="Courier New"><SPAN class=132071113-18072010></SPAN></FONT> </DIV> <DIV><FONT size=2 face="Courier New"><SPAN class=132071113-18072010>Nice.</SPAN></FONT></DIV> <DIV><FONT size=2 face="Courier New"><SPAN class=132071113-18072010>Two caveats though.</SPAN></FONT></DIV> <DIV><FONT size=2 face="Courier New"><SPAN class=132071113-18072010>1. If the value of a-value happens to be a procedure to be stored, it may unintentionally be called.</SPAN></FONT></DIV> <DIV><FONT size=2 face="Courier New"><SPAN class=132071113-18072010>2. a-value may be an expresssion that takes much computation. This computation is repeated every time the hash-ref line is evaluated.</SPAN></FONT></DIV> <DIV><FONT size=2 face="Courier New"><SPAN class=132071113-18072010></SPAN></FONT> </DIV> <DIV><FONT size=2 face="Courier New"><SPAN class=132071113-18072010>Simply helped of course: I make it a habbit always to write or to have macros expand to:</SPAN></FONT></DIV> <DIV><FONT size=2 face="Courier New"><SPAN class=132071113-18072010><SPAN class=132071113-18072010>(hash-ref a-hash a-key (lambda () a-value))</SPAN></SPAN></FONT></DIV> <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> <DIV><FONT size=2 face="Courier New"><SPAN class=132071113-18072010><SPAN class=132071113-18072010>Jos</SPAN></SPAN></FONT></DIV></BODY></HTML>