/usr/share/doc/swi-prolog-doc/UserGuide/sec-3.2.html

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<H2><A NAME="sec:3.2"><SPAN class="sec-nr">3.2</SPAN> <SPAN class="sec-title">Notational 
conventions</SPAN></A></H2>

<P>The text shown by the online manual uses some notational conventions. 
The various overview tools indicate candidate documentation cards with a <EM><A NAME="idx:summaryline:93">summary line</A></EM>. 
This line is of the form:
<BLOCKQUOTE>
&lt;<VAR>Identifier</VAR>&gt; &lt;<VAR>Formal&nbsp;Description</VAR>&gt; 
[``&lt;<VAR>Summary</VAR>&gt;'']
</BLOCKQUOTE>

<P>The `Identifier' is a single letter indicating the nature of the 
documentation card. The defined identifiers are: <B>B</B>rowser (Manual 
Tool), <B>C</B>lass, <B>E</B>xample, <B>K</B>eyword, <B>M</B>ethod,
<B>O</B>bject, <B>P</B>redicate, <B>R</B>esource, <B>T</B>opic and
<B>V</B>ariable (instance-variable).

<P>The `Formal Description' is a short description derived from the 
described object itself:

<P>
<CENTER>
<TABLE BORDER=2 FRAME=box RULES=groups>
<TR VALIGN=top><TD><TT>V</TT> class <CODE> - </CODE>selector: type</TD><TD>Variable 
that cannot be accessed directly </TD></TR>
<TR VALIGN=top><TD><TT>V</TT> class <CODE>&lt;- </CODE>selector: type</TD><TD>Variable 
that may be read, but not written </TD></TR>
<TR VALIGN=top><TD><TT>V</TT> class <CODE>&lt;-&gt;</CODE>selector: type</TD><TD>Variable 
that may be read and written </TD></TR>
<TR VALIGN=top><TD><TT>V</TT> class <CODE> -&gt;</CODE>selector: type</TD><TD>Variable 
that may only be written </TD></TR>
<TR VALIGN=top><TD><TT>M</TT> class <CODE> -&gt;</CODE>selector: type 
...</TD><TD>Send-Method with argument-types </TD></TR>
<TR VALIGN=top><TD><TT>M</TT> class <CODE>&lt;- </CODE>selector: type 
... <CODE>--&gt;</CODE>type</TD><TD>Get-Method with argument-types 
returning value of type </TD></TR>
<TR VALIGN=top><TD><TT>R</TT> Class.attribute: type</TD><TD>Class-variable 
with type </TD></TR>
</TABLE>

</CENTER>

<P>The same notational conventions are used in the running text of a 
card. See <A class="sec" href="sec-3.3.html">section 3.3.2</A>.

<H3><A NAME="sec:3.2.1"><SPAN class="sec-nr">3.2.1</SPAN> <SPAN class="sec-title">Argument 
types</SPAN></A></H3>

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

<P><A NAME="idx:argumenttype:94"></A><A NAME="idx:type:95"></A><font size=-1>XPCE</font> 
is a partially typed language. Types may be defined for both method 
arguments and instance variables. A type is represented by an instance 
of class <A class="" href="summary.html#class:type">type</A>. <font size=-1>XPCE</font> 
defines a conversion to create type objects from a textual 
representation. A full description of this conversion may be found in 
the online manual (method <A NAME="idx:typegetconvert:96"></A>`<B>type<CODE>&lt;-</CODE>convert</B>'). 
In this document we will summarise the most important types:

<P>
<UL>
<LI><I>int</I><BR>
<font size=-1>XPCE</font> integer datum.
<LI><I>&lt;<VAR>low</VAR>&gt;..&lt;<VAR>high</VAR>&gt;, &lt;<VAR>low</VAR>&gt;.., 
..&lt;<VAR>high</VAR>&gt;</I><BR>
Range of integers (including &lt;<VAR>low</VAR>&gt; and &lt;<VAR>high</VAR>&gt;). 
The latter two constructs indicate one-side-unbound integer. Both &lt;<VAR>low</VAR>&gt; 
and &lt;<VAR>high</VAR>&gt; can also be floating point numbers, 
indication a `real-range'.
<LI><I>any</I><BR>
Both integers and objects. Function objects will be evaluated. See <A class="sec" href="exeobjects.html">section 
10.2.2</A>.
<LI><I>&lt;<VAR>class-name</VAR>&gt;</I><BR>
Any instance of this class or one of its sub-classes. Class
<A class="" href="summary.html#class:object">object</A> is the root of 
the inheritance hierarchy. The type <TT>object</TT> is interpreted 
slightly different, as it does <EM>not</EM> accept instances of class <A class="" href="summary.html#class:function">function</A> 
or its subclasses. This implies that the type <TT>object</TT> forces 
functions to be evaluated.
<LI><I><TT>[</TT>&lt;<VAR>type</VAR>&gt;<TT>]</TT></I><BR>
Either this type or <A NAME="idx:default:97"></A><B>@default</B>. 
Trailing arguments to methods that accept <A NAME="idx:default:98"></A><B>@default</B> 
may be omitted.
<LI><I>&lt;<VAR>type</VAR>&gt;<TT>*</TT></I><BR>
Either this type or <A NAME="idx:nil:99"></A><B>@nil</B>.
<LI><I>&lt;<VAR>type</VAR>&gt; <TT>...</TT></I><BR>
Methods with this type specification accept any number of arguments that 
satisfy &lt;<VAR>type</VAR>&gt;.
<LI><I>{&lt;<VAR>atom1</VAR>&gt;,&lt;<VAR>atom2</VAR>&gt;, ...}</I><BR>
Any of these name objects.
</UL>

<P>For example, the <B><CODE>-&gt;</CODE>initialise</B> method of a 
graphical text object has type declaration:

<PRE class="code">
[char_array], [{left,center,right}], [font]
</PRE>

<P>The first argument is an instance of class <A class="" href="summary.html#class:char_array">char_array</A>, 
the super-class of <A class="" href="summary.html#class:name">name</A> 
and <A class="" href="summary.html#class:string">string</A>. The second 
argument either `left', `center' or `right' and the last argument is a 
font object. All arguments are between square brackets and may thus be 
omitted.

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