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<P><FONT SIZE="5">6.3 Multiple Language Systems</FONT><BR>
<P>With the prevalence of open systems and multi-vendor computing, it is often necessary
to construct systems consisting of programs written in a
number of different programming languages for a number of
different systems. For example, a particular functionality
might be implemented by a shellscript (invoked by the user)
that calls a C program that makes a network connection to a
Pascal program that queries a database. Quite often all
these programs must conspire closely to execute their
function. In the normal case, they must be written
separately. FunnelWeb allows them to be written as a whole.
<P>By creating a single FunnelWeb file that creates many
product files in different languages, the programmer can
describe the interaction between the different programs in
any manner desired. Furthermore, because the different
product files are all created in the same "text
space" (i.e. in a single FunnelWeb file), it is easy for
them to share information.
<P>For example, in one real application FunnelWeb was used
to create a system for printing
files on a laser
printer connected to a remote Vax
Unix machine from a local Vax VMS machine. The system
consisted of two files: a VMS DCL command procedure to run
on the local node, and a Unix shellscript to run on the
remote node. The user, by giving the print command, invoked
the local VMS command procedure, which in turn fired up the
remote Unix shellscript. The two scripts then cooperated to
transfer the files to be printed and print them.
<P>In addition to its usual documentation powers,
FunnelWeb assisted in the creation of this system in two
special ways. First, it allowed pieces of code from the two
different command procedures to be partially interwoven in a
description of their interaction. This is just not possible
with comments. Second, it facilitated the use of shared
information. For example, under some conditions, each file
to be printed would be renamed and copied to the remote
system using a particular constant filename
(e.g. "<TT>printfile.tmp</TT>"). FunnelWeb allowed this
constant filename to be included in a single macro
definition which was invoked in the definition of each of
the scripts. This ensured that the two scripts used the same
name.
<P>
<PRE>
@A The following macro contains the temporary
file name used to allow the two shellscripts to
transfer each file to be printed.
@$@<printfile@>@M==@{printme.txt@}
@A Here are the scripts for the local VMS node
and the remote UNIX node.
@O@<vmscommandprocedure.com@>==@{@-
DCL commands
copy @<printfile@> unixnode::
DCL commands
@}
@O@<unixshellscript@>==@{@-
unix commands
print @<printfile@>
unix commands
@}
</PRE>
<P>In the case of the printing system, the entire system
was described and defined in a single FunnelWeb
<SAMP>.fw</SAMP> file. In larger systems containing many
FunnelWeb <SAMP>.fw</SAMP> files for many different modules in
many different languages, the same trick can be pulled by
placing FunnelWeb macro definitions for shared values into
FunnelWeb include files. For example, a suite of
implementations of network nodes, with each implementation
being in a different programming language for a different
target machine, could all share a table of configuration
constants defined in macros in a FunnelWeb include file.
<P>In summary, FunnelWeb's macro and include file
mechanisms provide a simple way for programs written in
different languages to share information. This reduces
redundancy between the systems and hence the chance of
inconsistencies arising.
<P>
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