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Alan Johnsey wrote at 04/25/2013 10:04 PM:
<blockquote cite="mid:2A03BC0FCF734F198C813509E0ED875B@TheHPMachine"
type="cite">
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<font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;">(define x (make-posn 4 5))<o:p></o:p></span></font>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;">(define y (make-posn 4 5))</span></font></p>
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</blockquote>
[...]<br>
<blockquote cite="mid:2A03BC0FCF734F198C813509E0ED875B@TheHPMachine"
type="cite">
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<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;"><o:p></o:p></span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;">> (equal? x y)<o:p></o:p></span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;">#f</span></font></p>
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</blockquote>
[...]<br>
<blockquote cite="mid:2A03BC0FCF734F198C813509E0ED875B@TheHPMachine"
type="cite">
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<p class="MsoNormal"></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;">Adding #:transparent to
the posn struct definition makes x
equal? to both y and z as it should, and eq? gives #f when comparing x
and y as
it should.</span></font></p>
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<br>
Seems good for security that one can't use "equal?" and constructor
brute-force to determine the contents of an opaque struct.<br>
<br>
Neil V.<br>
<br>
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