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<h1>Variable names and data types</h1>
<h2>Variable names</h2>
<dl>
<dt><code>x</code></dt>
<dd>refers to the variable <code>x</code> in the immediate context</dd> 
<dt><code>~/x</code></dt>
<dd>refers to the variable <code>x</code> in the context one level up</dd>
<dt><code>/x</code></dt>
<dd>refers to the variable <code>x</code> in the root (topmost) context</dd> 
<dt><code>x!</code></dt><dd>refers to an Eden variable</dd></dl>
Note:
<UL>
<li>DoNaLD variables need to be declared before use.</li>
<li>Eden variables (ending with !) do not need to be declared and would not
be type-checked by DoNaLD.  To help the type-checker, it is advisible
to surround the variable with trunc() or float() to force the
expression to int or real type.</li>
<li><code>pi</code> is a predefined constant 3.14159.  It cannot be redefined
as a variable associated with any context.</li></UL>

<h2>Data types</h2>
<table>
<tr align="left"><th>Type</th><th>Example</th></tr>
<tr align="left"><td><code>int</code></td><td><code>34</code></td></tr>
<tr align="left"><td><code>real</code></td><td><code>10.0</code></td></tr>
<tr align="left"><td><code>char</code></td><td><code>"abc"</code></td></tr>
<tr align="left"><td><code>boolean</code></td><td><code>true, false</code></td></tr>
<tr align="left"><td><code>point</code></td><td><code>{50, 100}, {modulo @ angle}</code></td></tr>
<tr align="left"><td><code>line</code></td><td><code>[{10,10}, {80, 90}]</code></td></tr>
<tr align="left"><td><code>circle</code></td><td><code>circle(centre, radius), circle({500,500}, 400)</code></td></tr>
<tr align="left"><td><code>ellipse</code></td><td><code>ellipse(centre, major, minor)</code></td></tr>
<tr align="left"><td><code>rectangle</code></td><td><code>rectangle({100, 100}, point1)</code></td></tr>
<tr align="left"><td><code>image</code></td><td><code>I!ImageFile("gif", "hill.gif")</code></td></tr>
<TR ALIGN="left" VALIGN="top"><td><code>label</code></td><td><code>label L1, L2
<BR>L1 = label("abc", {100,100})
<BR>image img
<BR>L2 = label(img, {200,100})</code></td></tr>
<tr align="left"><td><code>openshape</code></td><td><code>openshape cross</code></td></tr>
<tr align="left"><td>&nbsp;</td><td><code>within cross {
<BR>&nbsp;&nbsp;line l1, l2
<BR>&nbsp;&nbsp;l1 = [{10, -10}, {-10, 10}]
<BR>&nbsp;&nbsp;l2 = [{10, 10}, {-10, -10}]
<BR>}</code></td></tr>
<TR ALIGN="left" VALIGN="top"><td><code>shape</code></td><td><code>shape S
<BR>S = trans(cross, 100, 200)</code></td></tr>
<TR ALIGN="left" VALIGN="top"><td><code>graph</code></td><td><code>func sqr { return $1 * $1; }
<BR>%donald
<BR>graph g
<BR>within g {
<BR>&nbsp;&nbsp;x&lt;i&gt; = 1.0 + &lt;i&gt;
<BR>&nbsp;&nbsp;f&lt;i&gt; = sqr!(x&lt;i&gt;)
<BR>&nbsp;&nbsp;nSegment = 9
<BR>&nbsp;&nbsp;node = [circle:circle({x&lt;i&gt; * 100, f&lt;i&gt; * 10}, 10);
<BR>&nbsp;&nbsp;&nbsp;&nbsp;label:label("(" // rtos(x&lt;i&gt;, ".0f") // "," // rtos(f&lt;i&gt;, ".0f") // ")", {x&lt;i&gt; * 100, f&lt;i&gt; * 10 + 20})]
<BR>&nbsp;&nbsp;segment = [line:[{x&lt;i-1&gt;*100, f&lt;i-1&gt;*10}, {x&lt;i&gt;*100, f&lt;i&gt;*10}]]
<BR>}</code></td></tr>
</table>

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