<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "> <div><br></div><div>If you tried this in Advanced, the highest HtDP teaching level, this program would work just fine: </div><div><br></div><div><blockquote type="cite" class=""><div>Welcome to DrScheme, version 4.0.2.5-svn28jul2008 [3m].</div><div>Language: Advanced Student custom; memory limit: 256 megabytes.</div><div>Teachpack: world.ss.</div><div>> (first (shared ((x (cons 1 x))) x))</div><div>1</div><div>> (second (shared ((x (cons 1 x))) x))</div><div>1</div><div>> (third (shared ((x (cons 1 x))) x))</div><div>1</div></blockquote><br></div><div><br></div><div>So this could be a bug, depending on what language you are using. Remember PLT Scheme isn't a language, it's a lot of languages. </div><div><br></div><div>-- Matthias</div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><div>On Jul 29, 2008, at 1:26 AM, Gregory Woodhouse wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"> I was under the impression that first was a synonym for car, second for cadr, etc. But apparently,, this isn't so with shared variables<div><br></div><div><div>> (shared ((a (cons 1 a))) (car a))</div><div>1</div><div>> (shared ((a (cons 1 a))) (cadr a))</div><div>1</div><div>> (shared ((a (cons 1 a))) (first a))</div><div>. . first: expected argument of type <non-empty list>; given #0=(1 . #0#)</div><div>> </div><div><br></div><br><div> <span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div><br class="Apple-interchange-newline"><br class="khtml-block-placeholder"></div><div>"We may with advantage at times forget what we know."</div><div>--Publilius Cyrus, c. 100 B.C.</div><div><br></div><div><div><a href="http://www.gwoodhouse.com">http://www.gwoodhouse.com</a></div><div><a href="http://GregWoodhouse.ImageKind.com">http://GregWoodhouse.ImageKind.com</a></div><div><br></div></div><div><br class="khtml-block-placeholder"></div><br class="Apple-interchange-newline"></span><br class="Apple-interchange-newline"></span> </div><br></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">_________________________________________________</div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><span class="Apple-converted-space"> </span>For list-related administrative tasks:</div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><span class="Apple-converted-space"> </span><a href="http://list.cs.brown.edu/mailman/listinfo/plt-scheme">http://list.cs.brown.edu/mailman/listinfo/plt-scheme</a></div> </blockquote></div><br></body></html>