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<div><a href="index.html" title="">Macaulay2Doc</a> > <a href="___The_sp__Macaulay2_splanguage.html" title="">The Macaulay2 language</a> > <a href="_for.html" title="for loops">for</a></div>
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<div><h1>for -- for loops</h1>
<div class="single"><h2>Synopsis</h2>
<ul><li><div class="list"><dl class="element"><dt class="heading">Usage: </dt><dd class="value"><div><tt>for i from m to n when p list x do z</tt></div>
</dd></dl>
</div>
</li>
<li><div class="single">Inputs:<ul><li><span><tt>m</tt>, <span>an <a href="___Z__Z.html">integer</a></span></span></li>
<li><span><tt>n</tt>, <span>an <a href="___Z__Z.html">integer</a></span></span></li>
</ul>
</div>
</li>
<li><div class="single">Consequences:<ul><li>The variable <tt>i</tt> is initialized to <tt>m</tt>. As long as <tt>i</tt> is not greater than <tt>n</tt>, evaluation of the loop continues. First <tt>p</tt> is evaluated. As long as the value of <tt>p</tt> is true, evaluation of the loop continues. Next <tt>x</tt> is evaluated and its value is saved, and <tt>z</tt> is evaluated and its value is discarded. Then <tt>i</tt> is incremented by 1, and the loop repeats. When the value of <tt>p</tt> is false, then the loop terminates, and the list of values of <tt>x</tt> is returned as the value of the entire expression.</li>
</ul>
</div>
</li>
<li><div class="single">Outputs:<ul><li><span>the list of values of the clause <tt>x</tt>, as desribed above</span></li>
</ul>
</div>
</li>
</ul>
</div>
<div class="single"><h2>Description</h2>
<div><div><h2>Synopsis</h2>
<ul><li><div class="list"><dl class="element"><dt class="heading">Usage: </dt><dd class="value"><div><tt>for i in v when p list x do z</tt></div>
</dd></dl>
</div>
</li>
<li>Inputs:<ul><li><span><tt>v</tt>, <span>a <a href="___Basic__List.html">basic list</a></span></span></li>
</ul>
</li>
<li>Consequences:<ul><li>The variable <tt>i</tt> is set to consecutive values of the list <tt>v</tt>. First <tt>p</tt> is evaluated. As long as the value of <tt>p</tt> is true, evaluation of the loop continues. Next <tt>x</tt> is evaluated, and its value is saved. Then <tt>z</tt> is evaluated and its value is discarded. Then the loop repeats with the next element of <tt>v</tt>. When the value of <tt>p</tt> is false, then the loop terminates, and the list of values of <tt>x</tt> is returned as the value of the entire expression.</li>
</ul>
</li>
</ul>
</div>
<h2>examples</h2>
<table class="examples"><tr><td><pre>i1 : for i from 1 to 5 when i < 15 list i^2 do print i
1
2
3
4
5
o1 = {1, 4, 9, 16, 25}
o1 : List</pre>
</td></tr>
<tr><td><pre>i2 : for i from 1 to 5 when i^2 < 15 list i^2 do print i
1
2
3
o2 = {1, 4, 9}
o2 : List</pre>
</td></tr>
</table>
<p>The <tt>do z</tt> clause may be omitted.</p>
<table class="examples"><tr><td><pre>i3 : for i from 1 to 5 when i < 15 list i^2
o3 = {1, 4, 9, 16, 25}
o3 : List</pre>
</td></tr>
</table>
<p>The <tt>from m</tt> clause may be omitted, in which case <tt>i</tt> starts with <tt>0</tt>.</p>
<table class="examples"><tr><td><pre>i4 : for i to 5 when i < 15 list i^2
o4 = {0, 1, 4, 9, 16, 25}
o4 : List</pre>
</td></tr>
</table>
<p>The <tt>when p</tt> clause may be omitted.</p>
<table class="examples"><tr><td><pre>i5 : for i to 5 list i^2
o5 = {0, 1, 4, 9, 16, 25}
o5 : List</pre>
</td></tr>
</table>
<p>The <tt>to n</tt> clause may be omitted.</p>
<table class="examples"><tr><td><pre>i6 : for i when i < 15 list i^2
o6 = {0, 1, 4, 9, 16, 25, 36, 49, 64, 81, 100, 121, 144, 169, 196}
o6 : List</pre>
</td></tr>
</table>
<p>The <tt>list x</tt> clause may be omitted.</p>
<table class="examples"><tr><td><pre>i7 : for i when i^2 < 15 do print i
0
1
2
3</pre>
</td></tr>
</table>
<p>If <a href="_continue.html" title="continue with the next iteration of a loop">continue</a> is executed by <tt>x</tt> then execution of <tt>x</tt> is interrupted, no value is added to the list, and iteration of the loop continues.</p>
<table class="examples"><tr><td><pre>i8 : for i from 0 when i < 10 list (if odd i then continue; i^2)
o8 = {0, 4, 16, 36, 64}
o8 : List</pre>
</td></tr>
</table>
<p>If <tt>continue w</tt> is executed by <tt>x</tt> then execution of <tt>x</tt> is interrupted, the value of <tt>w</tt> is added to the list, and iteration of the loop continues.</p>
<table class="examples"><tr><td><pre>i9 : for i from 0 when i < 10 list (if odd i then continue x; i^2)
o9 = {0, x, 4, x, 16, x, 36, x, 64, x}
o9 : List</pre>
</td></tr>
</table>
<p> If <tt>break v</tt> is executed by <tt>x</tt>, then the loop is stopped and <tt>v</tt> is returned as its value.</p>
<table class="examples"><tr><td><pre>i10 : for i from 0 when i < 10 list (if i== 5 then break i; i^2)
o10 = 5</pre>
</td></tr>
</table>
<p>If <a href="_break.html" title="break from a loop">break</a> is executed by <tt>x</tt>, then the loop is stopped and the list accumulated so far is returned as the value.</p>
<table class="examples"><tr><td><pre>i11 : for i from 0 when i < 10 list (if i== 5 then break; i^2)
o11 = {0, 1, 4, 9, 16}
o11 : List</pre>
</td></tr>
</table>
<p>The variable <tt>i</tt> is a new local variable whose scope includes only the expressions <tt>p</tt>, <tt>x</tt>, and <tt>y</tt>. The numbers <tt>m</tt> and <tt>n</tt> must be small integers that fit into a single word.</p>
<table class="examples"><tr><td><pre>i12 : for i in 0..3 list i^2
o12 = {0, 1, 4, 9}
o12 : List</pre>
</td></tr>
</table>
</div>
</div>
<div class="waystouse"><h2>For the programmer</h2>
<p>The object <a href="_for.html" title="for loops">for</a> is <span>a <a href="___Keyword.html">keyword</a></span>.</p>
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