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<A HREF="web.html"><FONT COLOR="#FFFFFF">7 Webmaking</FONT></A><BR>
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<P><FONT SIZE="5">5.10 FunnelWeb and Make</FONT><BR>
<P>The Unix <SAMP>Make</SAMP> program allows a set of
dependencies between a set of files to be described, and
then uses these dependencies to control the way in which the
files are created and updated. Typically, <SAMP>Make</SAMP> is
used to control the process of transforming a collection of
source code files to one or more executable files. As the
use of FunnelWeb implies an extra stage to this process, it
is natural to include the transformation of <SAMP>.fw</SAMP>
files to source code files as part of the <SAMP>Make</SAMP>
process. This is easy to do, but the user should be aware of
one aspect of FunnelWeb which can cause problems.
<P>It is often useful, when using FunnelWeb, to create a
FunnelWeb <SAMP>.fw</SAMP> file that generates more than one
product file. That is, a single <SAMP>.fw</SAMP> file may have
many macro definitions connected to product files so that
when the FunnelWeb <SAMP>.fw</SAMP> file is processed by
FunnelWeb, several files are created. For example, this
facility is convenient for placing a single package's
<SAMP>.h</SAMP> and <SAMP>.c</SAMP> files within the same
FunnelWeb <SAMP>.fw</SAMP> file.
<P>The use of multiple product files, however, provokes a
problem with dependencies. Suppose for example that a
FunnelWeb <SAMP>prog.fw</SAMP> produces two product files
<SAMP>proc.spec</SAMP> (a package specification) and
<SAMP>prog.body</SAMP> (a package body). If the package is
accessed in the way that packages normally are, it will be
quite common for the programmer to want to modify the
package body without modifying the program specification. So
the programmer will edit the <SAMP>prog.fw</SAMP> file to
change the package body. The result of running this through
FunnelWeb will be the desired new package body file.
However, FunnelWeb will also produce a new package
specification product file <I>even though it may be
identical to the previous version!</I> The result is that the
newly created (with a recent file date) specification
package file could provoke a huge remake of much of the
program in which it resides.
<P>To solve the problem, FunnelWeb includes a command line
option (<SAMP>D</SAMP> for
Delete),
which when turned on (using "<TT>+D</TT>") causes FunnelWeb
to suppress product and
documentation files that are identical to the previously
existing versions of the same files. For example, if, during
a FunnelWeb run, a macro was connected to a product file
called <SAMP>x.dat</SAMP>, and the macro expanded to
<I>exactly</I> the same text as is contained in
<SAMP>x.dat</SAMP> then FunnelWeb would simply <I>never
write the product file</I> , the file <SAMP>x.dat</SAMP> would be
untouched and, as a result, no further <SAMP>Make</SAMP>
propagations would take place.
<P>FunnelWeb implements this feature by writing each
product file to a temporary file with a temporary file name.
It then compares the temporary file with the target file. If
the two are identical, it deletes the temporary file. If the
two are different it deletes the target file and renames the
temporary file to the target file.
<P>Use of the <SAMP>D</SAMP> facility means that the
programmer need not be punished (by extra <SAMP>Make</SAMP>
propagations) for describing more than one product file in
the same FunnelWeb file.
<P>
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