File: design_numinst.html

package info (click to toggle)
funnelweb-doc 3.2d-4.2
links: PTS
area: main
in suites: forky, sid, trixie
size: 3,744 kB
sloc: perl: 241; makefile: 23
file content (204 lines) | stat: -rw-r--r-- 6,937 bytes
parent folder | download | duplicates (5)
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"
            "http://www.w3.org/TR/REC-html40/loose.dtd">

<HTML>
<!--
***********************************************************************
FUNNELWEB MANUAL WEB PAGE
=========================
Copyright (c) Ross N. Williams 1992,1999. All rights reserved.

Permission is granted to redistribute and use this manual in
any medium, with or without modification, provided that all
notices (including, without limitation, the copyright
notice, this permission notice, any record of modification,
and all legal notices) are preserved on all copies, that all
modifications are clearly marked, and that modified versions
are not represented as the original version unless all the
modifications since the manual's original release by Ross N.
Williams (www.ross.net) consist of translations or other
transformations that alter only the manual's form, not its
content. THIS MANUAL IS PROVIDED "AS IS" AND WITHOUT ANY
EXPRESS OR IMPLIED WARRANTIES, INCLUDING, WITHOUT
LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTIBILITY AND
FITNESS FOR A PARTICULAR PURPOSE. TO THE EXTENT PERMITTED BY
LAW THERE IS ABSOLUTELY NO WARRANTY.

***********************************************************************
-->

<HEAD>
<TITLE>2.9 Constraints On The Number of Instantiations</TITLE>
<STYLE TYPE="text/css"> <!-- A {text-decoration: none} // --> </STYLE>
</HEAD>
<BODY BACKGROUND="binary/background.gif"
      BGCOLOR="#FFFFFF"
      TEXT="#000000"
      VLINK="#660000"
      LINK="#FF0000"
      ALINK="#CC0000">

<TABLE WIDTH="490">
<TR>
<TD WIDTH="130" VALIGN="top">
<IMG SRC="binary/d_clear.gif" ALT="" WIDTH="130" HEIGHT="1"><BR>

<FONT SIZE="2">
<BR>

<A HREF="http://www.ross.net/"
 TARGET="rosshome"
 onClick="window.open('','rosshome','location,status,menubar,scrollbars,resizable',false).focus(); return true;"
>
 <IMG SRC="binary/rossnet_logo.gif"
  WIDTH="64" HEIGHT="32"
  BORDER="0" ALT="RossNet"
  HSPACE="0" VSPACE="1"></A><BR>
<BR>

<A HREF="../index.shtml"
 TARGET="funnelweb"
 onClick="window.open('','funnelweb','location,status,menubar,scrollbars,resizable',false).focus(); return true;"
>
 <IMG SRC="binary/linklogo.gif"
  WIDTH="64" HEIGHT="32"
  BORDER="0" ALT="FunnelWeb"
  HSPACE="0" VSPACE="1"></A><BR>
<BR>
<TABLE CELLSPACING=0 CELLPADDING=0 BORDER=0><TR><TD BGCOLOR="#000000">
<A HREF="../reference/index.html"
 TARGET="funnelwebreference"
 onClick="window.open('','funnelwebreference','location,status,menubar,scrollbars,resizable',false).focus(); return true;"
><FONT COLOR="#FFFFFF"><B>Reference</B></FONT></A><BR>
<BR>
<A HREF="../tutorial/index.html"
 TARGET="funnelwebtutorial"
 onClick="window.open('','funnelwebtutorial','location,status,menubar,scrollbars,resizable',false).focus(); return true;"
><FONT COLOR="#FFFFFF"><B>Tutorial</B></FONT></A><BR>
<BR>
<A HREF="index.html"><FONT COLOR="#FFFFFF"><B>Developer</B></FONT></A><BR>
<A HREF="compile.html"><FONT COLOR="#FFFFFF">1 Compile</FONT></A><BR>
<A HREF="design.html"><FONT COLOR="#FFFFFF">2 Design</FONT></A><BR>
<A HREF="implement.html"><FONT COLOR="#FFFFFF">3 Implement</FONT></A><BR>
<A HREF="modify.html"><FONT COLOR="#FFFFFF">4 Modify</FONT></A><BR>
<A HREF="misc.html"><FONT COLOR="#FFFFFF">5 Misc</FONT></A><BR>
<A HREF="gpl.html"><FONT COLOR="#FFFFFF">6 Licence</FONT></A><BR>

<BR>
<A HREF="search.html"><FONT COLOR="#FFFFFF"><B>SEARCH</B></FONT></A><BR>
</FONT>
</TD></TR></TABLE>


</TD>
<TD WIDTH="360" VALIGN="top">
<FONT SIZE="3">


<A HREF="index.html"><IMG SRC="binary/title.gif"
 WIDTH="316" HEIGHT="24"
 BORDER="0" ALT="FunnelWeb Developer Manual"
 HSPACE="0" VSPACE="0"></A>
<P><FONT SIZE="5">2.9 Constraints On The Number of Instantiations</FONT><BR>



<P>Experience with FunnelWeb&nbsp;V1 demonstrated the need
to be able to specify in each macro definitions how many times
the macro was expected to be called. FunnelWeb&nbsp;V1
generated an error if a macro is not used, but permited
macros to be called more than once. This caused problems for
macro libraries, many of whose macros were not called.

<P>By default, FunnelWeb&nbsp;V3.0 requires that each macro
(except for the ones attached to output files) be called
exactly once. However, it also provides syntax that allows
you to specify that a macro be allowed to be called
zero times or many times. This allows a macro to be
specified with the following permissible ranges of numbers
of calls depending on the presence or absence of
"<TT>@Z</TT>" and "<TT>@M</TT>":

<P>
<PRE>
   0..1          @$@&lt;Sloth@&gt;@Z...
      1          @$@&lt;Sloth@&gt;...
      1..n       @$@&lt;Sloth@&gt;@M...
   0.....n       @$@&lt;Sloth@&gt;@Z@M...
</PRE>

<P>The initial proposal for this syntax was to allow the
user to insert zero, one, or both of <SAMP>@?</SAMP> and
<SAMP>@M</SAMP> just after the <SAMP>@$</SAMP> of a macro
definition. Here are some other ideas that were considered
for the syntax of the calling number constraint.

<P>
<PRE>
@?@M@$@&lt;Slothy dogs@&gt;@(@5@)==@{@-
This is a short macro.
With only a line or two@}

@$@&lt;Slothy dogs@&gt;@?@M@(@5@)==@{@-
This is a short macro.
With only a line or two@}

@$@&lt;Slothy dogs@&gt;@(@5@)@?@M==@{@-
This is a short macro.
With only a line or two@
</PRE>

<P>The first form was rejected because it is a good visual
rule to start all the macros with <SAMP>@$</SAMP>. The second
form was rejected because it detaches the macro name from
the parameter list, thus making it look less like a call,
which is a desirable syntactic resonance. The third form is
messy, but was adopted with the change that <SAMP>@?</SAMP>
was changed to <SAMP>@M</SAMP>.

<P>After some thought, it was decided that the third
syntax was the best, but that the "<TT>@?</TT>" sequence be
reserved for a possible future conditional facility. It was
replaced by <SAMP>@Z</SAMP>.

<P>Example of final syntax:

<P>
<PRE>
@$@&lt;Slothy dogs@&gt;@(@5@)@Z@M+=@{@-
This is a short macro.
With only a line or two@}
</PRE>


<P>
<TABLE WIDTH="100%">
<TR>
<TD ALIGN="left"   VALIGN="bottom"><A HREF="design_filenames.html"><IMG SRC="binary/fw_left.gif" HEIGHT="32" WIDTH="32" BORDER="0" ALT="Prev"></A></TD>
<TD ALIGN="center" VALIGN="bottom"><A HREF="design.html"><IMG SRC="binary/fw_up.gif" HEIGHT="32" WIDTH="32" BORDER="0" ALT="Up"></A></TD>
<TD ALIGN="right"  VALIGN="bottom"><A HREF="design_docmac.html"><IMG SRC="binary/fw_right.gif" HEIGHT="32" WIDTH="32" BORDER="0" ALT="Next"></A></TD>
</TR>
</TABLE>



<P>
<HR>
<FONT SIZE="2">
<A HREF="mailto:webmaster@ross.net">Webmaster</A>&nbsp;&nbsp;&nbsp;
<A HREF="copyright.html">Copyright &copy; Ross N. Williams 1992,1999. All rights reserved.</A><BR>
</FONT>

</FONT>
</TD>
</TR>
</TABLE>


</BODY>

<!-- *********************************************************************** -->
<!--      End Of A FunnelWeb Manual Web Page (www.ross.net/funnelweb/)       -->
<!-- *********************************************************************** -->

</HTML>