<!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 6.00.6000.16481" name=GENERATOR> <STYLE></STYLE> </HEAD> <BODY bgColor=#ffffff> <DIV><FONT face="Courier New" size=2>Who can help me understand the following two ???s ?</FONT></DIV> <DIV><FONT face="Courier New" size=2></FONT> </DIV> <DIV><FONT face="Courier New" size=2>(eval ''#0=(1 . #0#)) ; --> #0=(1 . #0#) ; ok<BR>(define s (syntax-rules () ((_ x) (eval 'x))))<BR>;(s '#0=(1 . #0#)) --> bug ?: bad syntax in: #0=(1 . #0#) ; ???<BR>;(s ''#0=(1 . #0#)) --> bug syntax-source: expects argument of type <syntax>; given '#0=(1 . #0#) ; ???</FONT></DIV> <DIV> </DIV> <DIV><FONT face="Courier New" size=2>(define-syntax t (syntax-rules () ((_ x) (eval `x))))<BR>;(t '#0=(1 . #0#)) ; never returns ; ok, because quasiquote allocates and looks inside the circular list for unquote<BR>(t ,''#0=(1 . #0#)) ; --> #0=(1 . #0#) ; ok<BR>(t ','#0=(1 . #0#)) ; --> #0=(1 . #0#) ; ok</FONT></DIV> <DIV><FONT face="Courier New" size=2></FONT> </DIV> <DIV><FONT face="Courier New" size=2> <DIV><FONT face="Courier New" size=2>Is this a bug or am I missing some profound understanding?</FONT></DIV> <DIV><FONT face="Courier New" size=2>I know that the use of eval is not encouraged, but I need it in my own test system (allowing multiple values, checking standard output and checking for the correct error messages when expected)</FONT></DIV> <DIV>Thanks, Jos koot</DIV></FONT></DIV></BODY></HTML>