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<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"/><title>1.15&nbsp;An Arrow GUI: "arrow-gui.rkt"</title><link rel="stylesheet" type="text/css" href="../scribble.css" title="default"/><link rel="stylesheet" type="text/css" href="../racket.css" title="default"/><link rel="stylesheet" type="text/css" href="../manual-style.css" title="default"/><link rel="stylesheet" type="text/css" href="../manual-racket.css" title="default"/><link rel="stylesheet" type="text/css" href="../doc-site.css" title="default"/><script type="text/javascript" src="../scribble-common.js"></script><script type="text/javascript" src="../manual-racket.js"></script><script type="text/javascript" src="../doc-site.js"></script><script type="text/javascript" src="../local-redirect/local-redirect.js"></script><script type="text/javascript" src="../local-redirect/local-user-redirect.js"></script><!--[if IE 6]><style type="text/css">.SIEHidden { overflow: hidden; }</style><![endif]--></head><body id="doc-racket-lang-org"><div class="tocset"><div class="tocview"><div class="tocviewlist tocviewlisttopspace"><div class="tocviewtitle"><table cellspacing="0" cellpadding="0"><tr><td style="width: 1em;"><a href="javascript:void(0);" title="Expand/Collapse" class="tocviewtoggle" onclick="TocviewToggle(this,&quot;tocview_0&quot;);">&#9658;</a></td><td></td><td><a href="index.html" class="tocviewlink" data-pltdoc="x"><span style="font-style: italic">How to Design Programs</span> Teachpacks</a></td></tr></table></div><div class="tocviewsublisttop" style="display: none;" id="tocview_0"><table cellspacing="0" cellpadding="0"><tr><td align="right">1&nbsp;</td><td><a href="htdp.html" class="tocviewselflink" data-pltdoc="x">Ht<span class="mywbr"> &nbsp;</span>DP Teachpacks</a></td></tr><tr><td align="right">2&nbsp;</td><td><a href="2htdp2htdp.html" class="tocviewlink" data-pltdoc="x">Ht<span class="mywbr"> &nbsp;</span>DP/<span class="mywbr"> &nbsp;</span>2e Teachpacks</a></td></tr></table></div></div><div class="tocviewlist"><table cellspacing="0" cellpadding="0"><tr><td style="width: 1em;"><a href="javascript:void(0);" title="Expand/Collapse" class="tocviewtoggle" onclick="TocviewToggle(this,&quot;tocview_1&quot;);">&#9660;</a></td><td>1&nbsp;</td><td><a href="htdp.html" class="tocviewlink" data-pltdoc="x">Ht<span class="mywbr"> &nbsp;</span>DP Teachpacks</a></td></tr></table><div class="tocviewsublistbottom" style="display: block;" id="tocview_1"><table cellspacing="0" cellpadding="0"><tr><td align="right">1.1&nbsp;</td><td><a href="image.html" class="tocviewlink" data-pltdoc="x">Manipulating Images:<span class="mywbr"> &nbsp;</span> <span class="stt">"image.rkt"</span><a name="(idx._(gentag._0._(lib._teachpack/teachpack..scrbl)))"></a></a></td></tr><tr><td align="right">1.2&nbsp;</td><td><a href="world.html" class="tocviewlink" data-pltdoc="x">Simulations and Animations:<span class="mywbr"> &nbsp;</span> <span class="stt">"world.rkt"</span><a name="(idx._(gentag._1._(lib._teachpack/teachpack..scrbl)))"></a></a></td></tr><tr><td align="right">1.3&nbsp;</td><td><a href="convert.html" class="tocviewlink" data-pltdoc="x">Converting Temperatures:<span class="mywbr"> &nbsp;</span> <span class="stt">"convert.rkt"</span><a name="(idx._(gentag._2._(lib._teachpack/teachpack..scrbl)))"></a></a></td></tr><tr><td align="right">1.4&nbsp;</td><td><a href="guess.html" class="tocviewlink" data-pltdoc="x">Guessing Numbers:<span class="mywbr"> &nbsp;</span> <span class="stt">"guess.rkt"</span><a name="(idx._(gentag._3._(lib._teachpack/teachpack..scrbl)))"></a></a></td></tr><tr><td align="right">1.5&nbsp;</td><td><a href="master.html" class="tocviewlink" data-pltdoc="x">Master<span class="mywbr"> &nbsp;</span>Minding:<span class="mywbr"> &nbsp;</span> <span class="stt">"master.rkt"</span><a name="(idx._(gentag._4._(lib._teachpack/teachpack..scrbl)))"></a></a></td></tr><tr><td align="right">1.6&nbsp;</td><td><a href="master-play.html" class="tocviewlink" data-pltdoc="x">Playing Master<span class="mywbr"> &nbsp;</span>Mind:<span class="mywbr"> &nbsp;</span> <span class="stt">"master-<wbr></wbr>play.rkt"</span><a name="(idx._(gentag._5._(lib._teachpack/teachpack..scrbl)))"></a></a></td></tr><tr><td align="right">1.7&nbsp;</td><td><a href="draw.html" class="tocviewlink" data-pltdoc="x">Simple Drawing:<span class="mywbr"> &nbsp;</span> <span class="stt">"draw.rkt"</span><a name="(idx._(gentag._6._(lib._teachpack/teachpack..scrbl)))"></a></a></td></tr><tr><td align="right">1.8&nbsp;</td><td><a href="hangman.html" class="tocviewlink" data-pltdoc="x">Hangman:<span class="mywbr"> &nbsp;</span> <span class="stt">"hangman.rkt"</span><a name="(idx._(gentag._7._(lib._teachpack/teachpack..scrbl)))"></a></a></td></tr><tr><td align="right">1.9&nbsp;</td><td><a href="hangman-play.html" class="tocviewlink" data-pltdoc="x">Playing Hangman:<span class="mywbr"> &nbsp;</span> <span class="stt">"hangman-<wbr></wbr>play.rkt"</span><a name="(idx._(gentag._8._(lib._teachpack/teachpack..scrbl)))"></a></a></td></tr><tr><td align="right">1.10&nbsp;</td><td><a href="arrow.html" class="tocviewlink" data-pltdoc="x">Managing Control Arrows:<span class="mywbr"> &nbsp;</span> <span class="stt">"arrow.rkt"</span><a name="(idx._(gentag._9._(lib._teachpack/teachpack..scrbl)))"></a></a></td></tr><tr><td align="right">1.11&nbsp;</td><td><a href="docs.html" class="tocviewlink" data-pltdoc="x">Manipulating Simple HTML Documents:<span class="mywbr"> &nbsp;</span> <span class="stt">"docs.rkt"</span><a name="(idx._(gentag._10._(lib._teachpack/teachpack..scrbl)))"></a></a></td></tr><tr><td align="right">1.12&nbsp;</td><td><a href="dir.html" class="tocviewlink" data-pltdoc="x">Working with Files and Directories:<span class="mywbr"> &nbsp;</span> <span class="stt">"dir.rkt"</span><a name="(idx._(gentag._11._(lib._teachpack/teachpack..scrbl)))"></a></a></td></tr><tr><td align="right">1.13&nbsp;</td><td><a href="graphing.html" class="tocviewlink" data-pltdoc="x">Graphing Functions:<span class="mywbr"> &nbsp;</span> <span class="stt">"graphing.rkt"</span><a name="(idx._(gentag._12._(lib._teachpack/teachpack..scrbl)))"></a></a></td></tr><tr><td align="right">1.14&nbsp;</td><td><a href="gui.html" class="tocviewlink" data-pltdoc="x">Simple Graphical User Interfaces:<span class="mywbr"> &nbsp;</span> <span class="stt">"gui.rkt"</span><a name="(idx._(gentag._13._(lib._teachpack/teachpack..scrbl)))"></a></a></td></tr><tr><td align="right">1.15&nbsp;</td><td><a href="" class="tocviewselflink" data-pltdoc="x">An Arrow GUI:<span class="mywbr"> &nbsp;</span> <span class="stt">"arrow-<wbr></wbr>gui.rkt"</span><a name="(idx._(gentag._14._(lib._teachpack/teachpack..scrbl)))"></a></a></td></tr><tr><td align="right">1.16&nbsp;</td><td><a href="elevator.html" class="tocviewlink" data-pltdoc="x">Controlling an Elevator:<span class="mywbr"> &nbsp;</span> <span class="stt">"elevator.rkt"</span><a name="(idx._(gentag._15._(lib._teachpack/teachpack..scrbl)))"></a></a></td></tr><tr><td align="right">1.17&nbsp;</td><td><a href="lkup-gui.html" class="tocviewlink" data-pltdoc="x">Lookup GUI:<span class="mywbr"> &nbsp;</span> <span class="stt">"lkup-<wbr></wbr>gui.rkt"</span><a name="(idx._(gentag._16._(lib._teachpack/teachpack..scrbl)))"></a></a></td></tr><tr><td align="right">1.18&nbsp;</td><td><a href="guess-gui.html" class="tocviewlink" data-pltdoc="x">Guess GUI:<span class="mywbr"> &nbsp;</span> <span class="stt">"guess-<wbr></wbr>gui.rkt"</span><a name="(idx._(gentag._17._(lib._teachpack/teachpack..scrbl)))"></a></a></td></tr><tr><td align="right">1.19&nbsp;</td><td><a href="show-queen.html" class="tocviewlink" data-pltdoc="x">Queens:<span class="mywbr"> &nbsp;</span> <span class="stt">"show-<wbr></wbr>queen.rkt"</span><a name="(idx._(gentag._18._(lib._teachpack/teachpack..scrbl)))"></a></a></td></tr><tr><td align="right">1.20&nbsp;</td><td><a href="matrix.html" class="tocviewlink" data-pltdoc="x">Matrix Functions:<span class="mywbr"> &nbsp;</span> <span class="stt">"matrix.rkt"</span><a name="(idx._(gentag._19._(lib._teachpack/teachpack..scrbl)))"></a></a></td></tr></table></div></div></div><div class="tocsub"><div class="tocsubtitle">On this page:</div><table class="tocsublist" cellspacing="0"><tr><td><a href="#%28def._%28%28lib._htdp%2Farrow-gui..rkt%29._control%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">control</span></span></a></td></tr><tr><td><a href="#%28def._%28%28lib._htdp%2Farrow-gui..rkt%29._view%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">view</span></span></a></td></tr><tr><td><a href="#%28def._%28%28lib._htdp%2Farrow-gui..rkt%29._connect%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">connect</span></span></a></td></tr></table></div></div><div class="maincolumn"><div class="main"><div class="navsettop"><span class="navleft"><form class="searchform"><input class="searchbox" style="color: #888;" type="text" value="...search manuals..." title="Enter a search string to search the manuals" onkeypress="return DoSearchKey(event, this, &quot;6.1&quot;, &quot;../&quot;);" onfocus="this.style.color=&quot;black&quot;; this.style.textAlign=&quot;left&quot;; if (this.value == &quot;...search manuals...&quot;) this.value=&quot;&quot;;" onblur="if (this.value.match(/^ *$/)) { this.style.color=&quot;#888&quot;; this.style.textAlign=&quot;center&quot;; this.value=&quot;...search manuals...&quot;; }"/></form>&nbsp;&nbsp;<a href="../index.html" title="up to the documentation top" data-pltdoc="x" onclick="return GotoPLTRoot(&quot;6.1&quot;);">top</a></span><span class="navright">&nbsp;&nbsp;<a href="gui.html" title="backward to &quot;1.14 Simple Graphical User Interfaces: &quot;gui.rkt&quot;&quot;" data-pltdoc="x">&larr; prev</a>&nbsp;&nbsp;<a href="htdp.html" title="up to &quot;1 HtDP Teachpacks&quot;" data-pltdoc="x">up</a>&nbsp;&nbsp;<a href="elevator.html" title="forward to &quot;1.16 Controlling an Elevator: &quot;elevator.rkt&quot;&quot;" data-pltdoc="x">next &rarr;</a></span>&nbsp;</div><h4 x-source-module="(lib &quot;teachpack/teachpack.scrbl&quot;)" x-part-tag="&quot;arrow-gui&quot;">1.15<tt>&nbsp;</tt><a name="(part._arrow-gui)"></a><a name="(mod-path._htdp/arrow-gui)"></a>An Arrow GUI: <span class="stt">"arrow-gui.rkt"</span><a name="(idx._(gentag._14._(lib._teachpack/teachpack..scrbl)))"></a></h4><p><table cellspacing="0" cellpadding="0" class="defmodule"><tr><td align="left"><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=htdp-langs&amp;rel=beginner.html%23%2528form._%2528%2528lib._lang%252Fhtdp-beginner..rkt%2529._require%2529%2529&amp;version=6.1" class="RktStxLink Sq" data-pltdoc="x">require</a></span><span class="stt"> </span><a href="" class="RktModLink" data-pltdoc="x"><span class="RktSym">htdp/arrow-gui</span></a><span class="RktPn">)</span></td><td align="right"><span class="RpackageSpec"><span class="Smaller">&nbsp;package:</span> <span class="stt">htdp-lib</span></span></td></tr></table></p><p>The teachpack provides functions for creating and manipulating an arrow
GUI. We recommend using <a href="2htdpuniverse.html" class="RktModLink" data-pltdoc="x"><span class="RktSym">2htdp/universe</span></a> instead.</p><p><a name="(tech._modelt)"></a><span style="font-style: italic">modelT</span> <span class="RktPn">(</span><span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&amp;rel=function-contracts.html%23%2528form._%2528%2528lib._racket%252Fcontract%252Fbase..rkt%2529._-%7E3e%2529%2529&amp;version=6.1" class="RktStxLink Sq" data-pltdoc="x"><span class="nobreak">-&gt;</span></a></span><span class="stt"> </span><span class="RktSym">button%</span><span class="stt"> </span><span class="RktSym">event%</span><span class="stt"> </span><span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&amp;rel=booleans.html%23%2528def._%2528%2528lib._racket%252Fbool..rkt%2529._true%2529%2529&amp;version=6.1" class="RktValLink Sq" data-pltdoc="x">true</a></span><span class="RktPn">)</span></p><p>A <a href="#%28tech._modelt%29" class="techoutside" data-pltdoc="x"><span class="techinside">modelT</span></a> is a function that accepts and ignores two arguments.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._htdp/arrow-gui..rkt)._control))"></a><span title="Provided from: htdp/arrow-gui | Package: htdp-lib"><span class="RktSym"><a href="#%28def._%28%28lib._htdp%2Farrow-gui..rkt%29._control%29%29" class="RktValDef RktValLink" data-pltdoc="x">control</a></span></span><span class="RktPn"></span><span class="RktPn">)</span><span class="hspace">&nbsp;</span>&rarr;<span class="hspace">&nbsp;</span><span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&amp;rel=symbols.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._symbol%7E3f%2529%2529&amp;version=6.1" class="RktValLink Sq" data-pltdoc="x">symbol?</a></span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Reads out the current state of the message
field.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._htdp/arrow-gui..rkt)._view))"></a><span title="Provided from: htdp/arrow-gui | Package: htdp-lib"><span class="RktSym"><a href="#%28def._%28%28lib._htdp%2Farrow-gui..rkt%29._view%29%29" class="RktValDef RktValLink" data-pltdoc="x">view</a></span></span><span class="hspace">&nbsp;</span><span class="RktVar">s</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span>&rarr;<span class="hspace">&nbsp;</span><span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&amp;rel=booleans.html%23%2528def._%2528%2528lib._racket%252Fbool..rkt%2529._true%2529%2529&amp;version=6.1" class="RktValLink Sq" data-pltdoc="x">true</a></span></p></blockquote></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="RktVar">s</span><span class="hspace">&nbsp;</span>:<span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&amp;rel=data-structure-contracts.html%23%2528def._%2528%2528lib._racket%252Fcontract%252Fbase..rkt%2529._or%252Fc%2529%2529&amp;version=6.1" class="RktValLink Sq" data-pltdoc="x">or/c</a></span><span class="hspace">&nbsp;</span><span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&amp;rel=strings.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._string%7E3f%2529%2529&amp;version=6.1" class="RktValLink Sq" data-pltdoc="x">string?</a></span><span class="hspace">&nbsp;</span><span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&amp;rel=symbols.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._symbol%7E3f%2529%2529&amp;version=6.1" class="RktValLink Sq" data-pltdoc="x">symbol?</a></span><span class="RktPn">)</span></td></tr></table></blockquote></div><div class="SIntrapara">Displays <span class="RktVar">s</span> in the
message field.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._htdp/arrow-gui..rkt)._connect))"></a><span title="Provided from: htdp/arrow-gui | Package: htdp-lib"><span class="RktSym"><a href="#%28def._%28%28lib._htdp%2Farrow-gui..rkt%29._connect%29%29" class="RktValDef RktValLink" data-pltdoc="x">connect</a></span></span><span class="hspace">&nbsp;</span><span class="RktVar">l</span><span class="hspace">&nbsp;</span><span class="RktVar">r</span><span class="hspace">&nbsp;</span><span class="RktVar">u</span><span class="hspace">&nbsp;</span><span class="RktVar">d</span><span class="RktPn">)</span><span class="hspace">&nbsp;</span>&rarr;<span class="hspace">&nbsp;</span><span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&amp;rel=booleans.html%23%2528def._%2528%2528lib._racket%252Fbool..rkt%2529._true%2529%2529&amp;version=6.1" class="RktValLink Sq" data-pltdoc="x">true</a></span></p></blockquote></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="RktVar">l</span><span class="hspace">&nbsp;</span>:<span class="hspace">&nbsp;</span><a href="#%28tech._modelt%29" class="techoutside" data-pltdoc="x"><span class="techinside">modelT</span></a></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="RktVar">r</span><span class="hspace">&nbsp;</span>:<span class="hspace">&nbsp;</span><a href="#%28tech._modelt%29" class="techoutside" data-pltdoc="x"><span class="techinside">modelT</span></a></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="RktVar">u</span><span class="hspace">&nbsp;</span>:<span class="hspace">&nbsp;</span><a href="#%28tech._modelt%29" class="techoutside" data-pltdoc="x"><span class="techinside">modelT</span></a></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="RktVar">d</span><span class="hspace">&nbsp;</span>:<span class="hspace">&nbsp;</span><a href="#%28tech._modelt%29" class="techoutside" data-pltdoc="x"><span class="techinside">modelT</span></a></td></tr></table></blockquote></div><div class="SIntrapara">Connects four
controllers with the four directions in the arrow window.</div></p><p><div class="SIntrapara">Example:
</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="RktCmt">;</span><span class="RktCmt">&nbsp;</span><span class="RktCmt">Advanced</span></td></tr><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&amp;rel=define.html%23%2528form._%2528%2528lib._racket%252Fprivate%252Fbase..rkt%2529._define%2529%2529&amp;version=6.1" class="RktStxLink Sq" data-pltdoc="x">define</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym">make-model</span><span class="hspace">&nbsp;</span><span class="RktSym">dir</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&amp;rel=lambda.html%23%2528form._%2528%2528lib._racket%252Fprivate%252Fbase..rkt%2529._lambda%2529%2529&amp;version=6.1" class="RktStxLink Sq" data-pltdoc="x">lambda</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym">b</span><span class="hspace">&nbsp;</span><span class="RktSym">e</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&amp;rel=begin.html%23%2528form._%2528%2528quote._%7E23%7E25kernel%2529._begin%2529%2529&amp;version=6.1" class="RktStxLink Sq" data-pltdoc="x">begin</a></span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="#%28def._%28%28lib._htdp%2Farrow-gui..rkt%29._view%29%29" class="RktValLink" data-pltdoc="x">view</a></span><span class="hspace">&nbsp;</span><span class="RktSym">dir</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=reference&amp;rel=Writing.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._printf%2529%2529&amp;version=6.1" class="RktValLink Sq" data-pltdoc="x">printf</a></span><span class="hspace">&nbsp;</span><span class="RktVal">"~a ~n"</span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="#%28def._%28%28lib._htdp%2Farrow-gui..rkt%29._control%29%29" class="RktValLink" data-pltdoc="x">control</a></span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;</span></td></tr><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="#%28def._%28%28lib._htdp%2Farrow-gui..rkt%29._connect%29%29" class="RktValLink" data-pltdoc="x">connect</a></span><span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym">make-model</span><span class="hspace">&nbsp;</span><span class="RktVal">"left"</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym">make-model</span><span class="hspace">&nbsp;</span><span class="RktVal">"right"</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym">make-model</span><span class="hspace">&nbsp;</span><span class="RktVal">"up"</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="RktPn">(</span><span class="RktSym">make-model</span><span class="hspace">&nbsp;</span><span class="RktVal">"down"</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></blockquote></div><div class="SIntrapara">Now click on the four arrows. The message field contains the current
direction, the print-out the prior contents of the message field.</div></p><div class="navsetbottom"><span class="navleft"><form class="searchform"><input class="searchbox" style="color: #888;" type="text" value="...search manuals..." title="Enter a search string to search the manuals" onkeypress="return DoSearchKey(event, this, &quot;6.1&quot;, &quot;../&quot;);" onfocus="this.style.color=&quot;black&quot;; this.style.textAlign=&quot;left&quot;; if (this.value == &quot;...search manuals...&quot;) this.value=&quot;&quot;;" onblur="if (this.value.match(/^ *$/)) { this.style.color=&quot;#888&quot;; this.style.textAlign=&quot;center&quot;; this.value=&quot;...search manuals...&quot;; }"/></form>&nbsp;&nbsp;<a href="../index.html" title="up to the documentation top" data-pltdoc="x" onclick="return GotoPLTRoot(&quot;6.1&quot;);">top</a></span><span class="navright">&nbsp;&nbsp;<a href="gui.html" title="backward to &quot;1.14 Simple Graphical User Interfaces: &quot;gui.rkt&quot;&quot;" data-pltdoc="x">&larr; prev</a>&nbsp;&nbsp;<a href="htdp.html" title="up to &quot;1 HtDP Teachpacks&quot;" data-pltdoc="x">up</a>&nbsp;&nbsp;<a href="elevator.html" title="forward to &quot;1.16 Controlling an Elevator: &quot;elevator.rkt&quot;&quot;" data-pltdoc="x">next &rarr;</a></span>&nbsp;</div></div></div><div id="contextindicator">&nbsp;</div></body></html>