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<HTML><HEAD><TITLE>5.4 Truth Values</TITLE><LINK href="ozdoc.css" rel="stylesheet" type="text/css"></HEAD><BODY><TABLE align="center" border="0" cellpadding="6" cellspacing="6" class="nav"><TR bgcolor="#DDDDDD"><TD><A href="name.html#section.literals.names"><< Prev</A></TD><TD><A href="node7.html">- Up -</A></TD><TD><A href="unit.html#section.literals.unit">Next >></A></TD></TR></TABLE><DIV id="section.literals.bool"><H2><A name="section.literals.bool">5.4 Truth Values</A></H2><P> The module <A name="label157"></A><SPAN class="index"><CODE>Bool</CODE></SPAN> contains procedures operating on the truth values <A name="label158"></A><SPAN class="index"><CODE><SPAN class="keyword">true</SPAN></CODE></SPAN> and <A name="label159"></A><SPAN class="index"><CODE><SPAN class="keyword">false</SPAN></CODE></SPAN>, which denote names. </P><DL><DT><A name="label160"></A><SPAN class="index"><CODE>IsBool</CODE></SPAN> <A name="label162"></A> </DT><DD><BLOCKQUOTE class="synopsis"><P><CODE>{Bool<SPAN class="keyword">.</SPAN>is </CODE><CODE>+<I>X</I></CODE><CODE> </CODE><CODE>?<I>B</I></CODE><CODE>}</CODE> </P></BLOCKQUOTE></DD><DD><P>tests whether <CODE><I>X</I></CODE> is <CODE><SPAN class="keyword">true</SPAN></CODE> or <CODE><SPAN class="keyword">false</SPAN></CODE>. </P></DD><DT><A name="label163"></A><SPAN class="index"><CODE>Not</CODE></SPAN> <A name="label164"></A> </DT><DD><BLOCKQUOTE class="synopsis"><P><CODE>{Bool<SPAN class="keyword">.</SPAN><SPAN class="string">'not'</SPAN> </CODE><CODE>+<I>B1</I></CODE><CODE> </CODE><CODE>?<I>B2</I></CODE><CODE>}</CODE> </P></BLOCKQUOTE></DD><DD><P>returns the negation of truth value <CODE><I>B1</I></CODE>. </P></DD><DT><A name="label165"></A><SPAN class="index"><CODE>And</CODE></SPAN> <A name="label166"></A> </DT><DD><BLOCKQUOTE class="synopsis"><P><CODE>{Bool<SPAN class="keyword">.</SPAN>and </CODE><CODE>+<I>B1</I></CODE><CODE> </CODE><CODE>+<I>B2</I></CODE><CODE> </CODE><CODE>?<I>B3</I></CODE><CODE>}</CODE> </P></BLOCKQUOTE></DD><DD><P>returns the conjunction of truth values <CODE><I>B1</I></CODE> and <CODE><I>B2</I></CODE>. Note that <CODE>And</CODE> is different from conditional conjunction available via the keyword <A name="label167"></A><SPAN class="index"><CODE><SPAN class="keyword">andthen</SPAN></CODE></SPAN> in that it always evaluates its second argument. </P><P> For instance, <CODE><SPAN class="keyword">false</SPAN> <SPAN class="keyword">andthen</SPAN> P</CODE> reduces without reducing application of <CODE>P</CODE>, whereas reduction of <CODE>{And <SPAN class="keyword">false</SPAN> P}</CODE> always applies <CODE>P</CODE>. </P></DD><DT><A name="label168"></A><SPAN class="index"><CODE>Or</CODE></SPAN> <A name="label169"></A> </DT><DD><BLOCKQUOTE class="synopsis"><P><CODE>{Bool<SPAN class="keyword">.</SPAN><SPAN class="string">'or'</SPAN> </CODE><CODE>+<I>B1</I></CODE><CODE> </CODE><CODE>+<I>B2</I></CODE><CODE> </CODE><CODE>?<I>B3</I></CODE><CODE>}</CODE> </P></BLOCKQUOTE></DD><DD><P>returns the disjunction of truth values <CODE><I>B1</I></CODE> and <CODE><I>B2</I></CODE>. Note that <CODE>Or</CODE> is different from conditional disjunction available via the keyword <A name="label170"></A><SPAN class="index"><CODE><SPAN class="keyword">orelse</SPAN></CODE></SPAN> in that it always evaluates its second argument. </P><P> For instance, <CODE><SPAN class="keyword">true</SPAN> <SPAN class="keyword">orelse</SPAN> P</CODE> reduces without reducing application of <CODE>P</CODE>, whereas reduction of <CODE>{Or <SPAN class="keyword">true</SPAN> P}</CODE> always applies <CODE>P</CODE>. </P></DD></DL><P> </P></DIV><TABLE align="center" border="0" cellpadding="6" cellspacing="6" class="nav"><TR bgcolor="#DDDDDD"><TD><A href="name.html#section.literals.names"><< Prev</A></TD><TD><A href="node7.html">- Up -</A></TD><TD><A href="unit.html#section.literals.unit">Next >></A></TD></TR></TABLE><HR><ADDRESS><A href="http://www.ps.uni-sb.de/~duchier/">Denys Duchier</A>, <A href="http://www.ps.uni-sb.de/~kornstae/">Leif Kornstaedt</A> and <A href="http://www.ps.uni-sb.de/~schulte/">Christian Schulte</A><BR><SPAN class="version">Version 1.4.0 (20090610)</SPAN></ADDRESS></BODY></HTML>
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