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<H2><A NAME="sec:5.8"><SPAN class="sec-nr">5.8</SPAN> <SPAN class="sec-title">Operators 
and modules</SPAN></A></H2>

<A NAME="sec:moduleop"></A>

<P>Operators (<A class="sec" href="operators.html">section 4.23</A>) are 
local to modules, where the initial table behaves as if it is copied 
from the module <CODE>user</CODE> (see
<A class="sec" href="resmodules.html">section 5.10</A>). A specific 
operator can be disabled inside a module using <CODE>:- op(0, Type, 
Name)</CODE>. Inheritance from the public table can be restored using <CODE>:- 
op(-1, Type, Name)</CODE>.

<P>In addition to using the <A NAME="idx:op3:1260"></A><A class="pred" href="operators.html#op/3">op/3</A> 
directive, operators can be declared in the <A NAME="idx:module2:1261"></A><A class="pred" href="defmodule.html#module/2">module/2</A> 
directive as shown below. Such operator declarations are visible inside 
the module and importing such a module makes the operators visible in 
the target module. Exporting operators is typically used by modules that 
implement sub-languages such as chr (see
<A class="sec" href="chr.html">chapter 7</A>). The example below is 
copied from the library
<CODE>library(clpfd)</CODE>.

<PRE class="code">
:- module(clpfd,
          [ op(760, yfx, #&lt;==&gt;),
            op(750, xfy, #==&gt;),
            op(750, yfx, #&lt;==),
            op(740, yfx, #\/),
            ...
            (#&lt;==&gt;)/2,
            (#==&gt;)/2,
            (#&lt;==)/2,
            (#\/)/2,
            ...
          ]).
</PRE>

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