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    <? prevnext "<h1>Tcl Example #2</h1>" ?>

    Something you can't do in Perl, Python or PHP is create new
    command structures:

    <pre>
<span class="keyword">proc</span> <span class="function-name">do</span> {body <span class="keyword">while</span> expression} {
    <span class="keyword">uplevel</span> $body
    <span class="keyword">while</span> { [uplevel expr $expression] } {
	<span class="keyword">uplevel</span> $body
    }
}

set i 0
do {
    puts $i
    incr i
} <span class="keyword">while</span> {$i &lt; 0}</pre>


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