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assert.html
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<html>
<head>
<meta charset='utf-8'>
<title>assert</title>
</head>
<body>
<h1>assert</h1>
<h2>Syntax</h2>
<font size="+1"><b>assert</b> <i>trueFalseExpn</i><p>
</p></font>
<h2>Description</h2>
An <b>assert</b> statement is used to make sure that a certain requirement is met. This requirement is given by the <i>trueFalseExpn</i>. The <i>trueFalseExpn </i>is evaluated. If it is true, all is well and execution continues. If it is false, execution is terminated with an appropriate message.<p>
</p>
<h2>Example</h2>
Make sure that <i>n</i> is positive.<p>
</p>
<pre><code> assert n > 0</code></pre>
<h2>Example</h2>
This program assumes that the <i>textFile </i>exists and can be opened, in other words, that the <b>open</b> will set the <i>fileNumber </i>to a positive stream number. If this is not true, the programmer wants the program halted immediately.<p>
</p>
<pre><code> var fileNumber : int
open : fileNumber, "textFile", read
assert fileNumber > 0</code></pre>
<h2>Details</h2>
In some Turing systems, checking can be turned off. If checking is turned off, <b>assert</b> statements may be ignored and as a result never cause termination.<p>
</p>
</body>
</html>