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Hello, <br>
<br>
I have to make a function which do nothing with the special key's.<br>
According to the manual I can use this : <br>
<br>
<br>
<div class="SIntrapara">Here is a typical key-event handler:</div>
<div class="SIntrapara">
<blockquote class="SCodeFlow">
<table class="RktBlk" cellspacing="0">
<tbody>
<tr>
<td><span class="RktPn">(</span><span class="RktSym"><a
class="RktStxLink"
href="http://docs.racket-lang.org/reference/define.html?q=on-key#%28form._%28%28lib._racket/private/base..rkt%29._define%29%29"
pltdoc="x">define</a></span><span class="hspace"> </span><span
class="RktPn">(</span><span class="RktSym">change</span><span
class="hspace"> </span><span class="RktSym">w</span><span
class="hspace"> </span><span class="RktSym">a-key</span><span
class="RktPn">)</span></td>
</tr>
<tr>
<td><span class="hspace"> </span><span class="RktPn">(</span><span
class="RktSym"><a class="RktStxLink"
href="http://docs.racket-lang.org/reference/if.html?q=on-key#%28form._%28%28lib._racket/private/letstx-scheme..rkt%29._cond%29%29"
pltdoc="x">cond</a></span></td>
</tr>
<tr>
<td><span class="hspace"> </span><span class="RktPn">[</span><span
class="RktPn">(</span><span class="RktSym"><a
class="RktValLink"
href="http://docs.racket-lang.org/teachpack/2htdpuniverse.html?q=on-key#%28def._%28%28lib._2htdp/universe..rkt%29._key%7E3d%7E3f%29%29"
pltdoc="x">key=?</a></span><span class="hspace"> </span><span
class="RktSym">a-key</span><span class="hspace"> </span><span
class="RktVal">"left"</span><span class="RktPn">)</span><span
class="hspace"> </span><span class="RktPn">(</span><span
class="RktSym">world-go</span><span class="hspace"> </span><span
class="RktSym">w</span><span class="hspace"> </span><span
class="RktSym"><span class="nobreak">-D</span>ELTA</span><span
class="RktPn">)</span><span class="RktPn">]</span></td>
</tr>
<tr>
<td><span class="hspace"> </span><span class="RktPn">[</span><span
class="RktPn">(</span><span class="RktSym"><a
class="RktValLink"
href="http://docs.racket-lang.org/teachpack/2htdpuniverse.html?q=on-key#%28def._%28%28lib._2htdp/universe..rkt%29._key%7E3d%7E3f%29%29"
pltdoc="x">key=?</a></span><span class="hspace"> </span><span
class="RktSym">a-key</span><span class="hspace"> </span><span
class="RktVal">"right"</span><span class="RktPn">)</span><span
class="hspace"> </span><span class="RktPn">(</span><span
class="RktSym">world-go</span><span class="hspace"> </span><span
class="RktSym">w</span><span class="hspace"> </span><span
class="RktSym">+DELTA</span><span class="RktPn">)</span><span
class="RktPn">]</span></td>
</tr>
<tr>
<td><span class="hspace"> </span><span class="RktPn">[</span><span
class="RktPn">(</span><span class="RktSym"><a
class="RktValLink"
href="http://docs.racket-lang.org/reference/generic-numbers.html?q=on-key#%28def._%28%28quote._%7E23%7E25kernel%29._%7E3d%29%29"
pltdoc="x">=</a></span><span class="hspace"> </span><span
class="RktPn">(</span><span class="RktSym"><a
class="RktValLink"
href="http://docs.racket-lang.org/reference/strings.html?q=on-key#%28def._%28%28quote._%7E23%7E25kernel%29._string-length%29%29"
pltdoc="x">string-length</a></span><span
class="hspace"> </span><span class="RktSym">a-key</span><span
class="RktPn">)</span><span class="hspace"> </span><span
class="RktVal">1</span><span class="RktPn">)</span><span
class="hspace"> </span><span class="RktSym">w</span><span
class="RktPn">]</span><span class="hspace"> </span><span
class="RktCmt">;</span><span class="RktCmt"> </span><span
class="RktCmt">order-free checking</span></td>
</tr>
<tr>
<td><span class="hspace"> </span><span class="RktPn">[</span><span
class="RktPn">(</span><span class="RktSym"><a
class="RktValLink"
href="http://docs.racket-lang.org/teachpack/2htdpuniverse.html?q=on-key#%28def._%28%28lib._2htdp/universe..rkt%29._key%7E3d%7E3f%29%29"
pltdoc="x">key=?</a></span><span class="hspace"> </span><span
class="RktSym">a-key</span><span class="hspace"> </span><span
class="RktVal">"up"</span><span class="RktPn">)</span><span
class="hspace"> </span><span class="RktPn">(</span><span
class="RktSym">world-go</span><span class="hspace"> </span><span
class="RktSym">w</span><span class="hspace"> </span><span
class="RktSym"><span class="nobreak">-D</span>ELTA</span><span
class="RktPn">)</span><span class="RktPn">]</span></td>
</tr>
<tr>
<td><span class="hspace"> </span><span class="RktPn">[</span><span
class="RktPn">(</span><span class="RktSym"><a
class="RktValLink"
href="http://docs.racket-lang.org/teachpack/2htdpuniverse.html?q=on-key#%28def._%28%28lib._2htdp/universe..rkt%29._key%7E3d%7E3f%29%29"
pltdoc="x">key=?</a></span><span class="hspace"> </span><span
class="RktSym">a-key</span><span class="hspace"> </span><span
class="RktVal">"down"</span><span class="RktPn">)</span><span
class="hspace"> </span><span class="RktPn">(</span><span
class="RktSym">world-go</span><span class="hspace"> </span><span
class="RktSym">w</span><span class="hspace"> </span><span
class="RktSym">+DELTA</span><span class="RktPn">)</span><span
class="RktPn">]</span></td>
</tr>
<tr>
<td><span class="hspace"> </span><span class="RktPn">[</span><span
class="RktSym"><a class="RktStxLink"
href="http://docs.racket-lang.org/reference/if.html?q=on-key#%28form._%28%28lib._racket/private/letstx-scheme..rkt%29._else%29%29"
pltdoc="x">else</a></span><span class="hspace"> </span><span
class="RktSym">w</span><span class="RktPn">]</span><span
class="RktPn">)</span><span class="RktPn">)</span></td>
</tr>
</tbody>
</table>
</blockquote>
</div>
<br>
<br>
But Can I use this if I want that if a special-key is used nothing
happens. <br>
<br>
<br>
[key?a-key "/t") ()]<br>
<br>
Roelof<br>
<br>
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