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<div class="subsection-level-extent" id="while">
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<h4 class="subsection" id="while-1">5.23.5 while</h4>
<a class="index-entry-id" id="index-while"></a>
<p><code class="code">groff</code> provides a looping construct: the <code class="code">while</code> request.
Its syntax matches the <code class="code">if</code> request.
</p>
<a class="index-entry-id" id="index-body_002c-of-a-while-request"></a>
<dl class="first-deffn">
<dt class="deffn" id="index-_002ewhile"><span class="category-def">Request: </span><span><strong class="def-name"><code class="t">.while</code></strong> <var class="def-var-arguments">cond-expr anything</var><a class="copiable-link" href='#index-_002ewhile'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-while-1"></a>
<p>Evaluate the conditional expression <var class="var">cond-expr</var>, and repeatedly
execute <var class="var">anything</var> unless and until <var class="var">cond-expr</var> evaluates false.
<var class="var">anything</var>, which is often a conditional block, is referred to as
the <code class="code">while</code> request’s <em class="dfn">body</em>.
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">.nr a 0 1
.while (\na < 9) \{\
\n+a,
.\}
\n+a
⇒ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10
</pre></div></div>
<a class="index-entry-id" id="index-de-request_002c-and-while"></a>
<p>GNU <code class="code">troff</code> treats the body of a <code class="code">while</code> request similarly to
that of a <code class="code">de</code> request (albeit one not read in copy
mode<a class="footnote" id="DOCF94" href="groff.html_fot.html#FOOT94"><sup>94</sup></a>), but stores it under an internal name
and deletes it when the loop finishes. The operation of a macro
containing a <code class="code">while</code> request can slow significantly if the
<code class="code">while</code> body is large. Each time the macro is executed, the
<code class="code">while</code> body is parsed and stored again.
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">.de xxx
. nr num 10
. while (\\n[num] > 0) \{\
. \" many lines of code
. nr num -1
. \}
..
</pre></div></div>
<a class="index-entry-id" id="index-recursive-macros"></a>
<a class="index-entry-id" id="index-macros_002c-recursive"></a>
<p>An often better solution—and one that is more portable, since
<abbr class="acronym">AT&T</abbr> <code class="code">troff</code> lacked the <code class="code">while</code> request—is to
instead write a recursive macro. It will be parsed only
once.<a class="footnote" id="DOCF95" href="groff.html_fot.html#FOOT95"><sup>95</sup></a>
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">.de yyy
. if (\\n[num] > 0) \{\
. \" many lines of code
. nr num -1
. yyy
. \}
..
.
.de xxx
. nr num 10
. yyy
..
</pre></div></div>
<p>To prevent infinite loops, the default number of available recursion
levels is 1,000 or somewhat less.<a class="footnote" id="DOCF96" href="groff.html_fot.html#FOOT96"><sup>96</sup></a> You can
disable this protective measure, or raise the limit, by setting the
<code class="code">slimit</code> register. See <a class="xref" href="Debugging.html">Debugging</a>.
</p>
<p>As noted above, if a <code class="code">while</code> body begins with a conditional block,
its closing brace must end an input line.
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">.if 1 \{\
. nr a 0 1
. while (\n[a] < 10) \{\
. nop \n+[a]
.\}\}
error→ unbalanced brace escape sequences
</pre></div></div>
</dd></dl>
<dl class="first-deffn">
<dt class="deffn" id="index-_002ebreak"><span class="category-def">Request: </span><span><strong class="def-name"><code class="t">.break</code></strong><a class="copiable-link" href='#index-_002ebreak'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-break-2"></a>
<a class="index-entry-id" id="index-while-request_002c-confusing-with-br"></a>
<a class="index-entry-id" id="index-break-request_002c-in-a-while-loop"></a>
<a class="index-entry-id" id="index-continue-request_002c-in-a-while-loop"></a>
<p>Exit a <code class="code">while</code> loop. Do not confuse this request with a
typographical break or the <code class="code">br</code> request.
</p></dd></dl>
<dl class="first-deffn">
<dt class="deffn" id="index-_002econtinue"><span class="category-def">Request: </span><span><strong class="def-name"><code class="t">.continue</code></strong><a class="copiable-link" href='#index-_002econtinue'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-continue"></a>
<p>Skip the remainder of a <code class="code">while</code> loop’s body, immediately starting
the next iteration.
</p></dd></dl>
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