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<TITLE>1.3 An Architectural Overview</TITLE>
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<A HREF="intro.html"><FONT COLOR="#FFFFFF">1 Introduction</FONT></A><BR>
<A HREF="interface.html"><FONT COLOR="#FFFFFF">2 Interface</FONT></A><BR>
<A HREF="scanner.html"><FONT COLOR="#FFFFFF">3 Scanner</FONT></A><BR>
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<P><FONT SIZE="5">1.3 An Architectural Overview</FONT><BR>
<P>An understanding of the internals of FunnelWeb assists
with understanding its operation. During a single run,
FunnelWeb reads and processes a single input file called the
<STRONG>input file</STRONG> (also called the
<STRONG>FunnelWeb file</STRONG>). The file is processed by
passing it through a series of stages called
<STRONG>phases</STRONG>. The result is that some
<STRONG>output files</STRONG> are generated. A
<STRONG>journal file</STRONG> is generated containing a copy
of the messages that appear on the console during the
FunnelWeb run. A <STRONG>listing file</STRONG> is created
containing a summary of the run, including any error
messages. A <STRONG>documentation</STRONG> file is generated
containing typesetter commands that when fed into a
typesetter program will result in printed documentation.
Finally, one or more <STRONG>product files</STRONG> are
generated containing the result of unscrambling the macro
definitions of the input file.
<P>
<PRE>
.fw Input File
(FunnelWeb file)
V
+---------+ \
| Scanner | |
+---------+ |
V |
+--------+ |
| Parser | |
+--------+ |
V |
+----------+ >----+--------+
| Analyser | | | |
+----------+ | | |
V | | |
+-------+-------+ | V V
V V | | |
+--------+ +-------+ | | |
| Tangle | | Weave | | | |
+--------+ +-------+ / | |
| | | |
V V V V
Product Documentation Listing Journal
Files File File File
</PRE>
<CENTER><B>FunnelWeb's processing phases</B><BR></CENTER>
<P>These files need not all be generated on any particular FunnelWeb run.
Whether each output file appears, is controlled by command line options.
<P>FunnelWeb processes each input file in a sequence of phases.
If an error occurs during a phase, no subsequent phases are executed.
<P>The phases are briefly described below.
<P><BLOCKQUOTE><B>The
Scanner</B> reads the input file,
expands and reads in include files, scans the
input stream, processes pragmas and typesetter
directives, and parses all the FunnelWeb special
sequences. The result is a list of tokens that is
handed to the parser.</BLOCKQUOTE>
<P><BLOCKQUOTE><B>The Parser</B> reads
the scanner's token list and parses it, constructing a
document list and a macro
table. which are passed to later phases.</BLOCKQUOTE>
<P><BLOCKQUOTE><B>The Analyser</B> examines
the macro table generated by the parser
and performs a number of checks of the macro structures
that the parser could not make on its single pass.
For example, the
analyser detects and flags unused macros and recursive macros. The
analyser forms the final stage of FunnelWeb's front-end processing.</BLOCKQUOTE>
<P><BLOCKQUOTE><B>Tangle</B> expands certain macros in the macro table
to generate one or more product files.</BLOCKQUOTE>
<P><BLOCKQUOTE><B>Weave</B> uses the document list to generate
a documentation file.</BLOCKQUOTE>
<P>A single run through these phases constitutes a single invocation of
<STRONG>FunnelWeb proper</STRONG>. Most invocations of the
<STRONG>FunnelWeb program</STRONG>
will consist only of a single execution of FunnelWeb proper. However,
FunnelWeb also provides a command shell that provides many useful commands,
including a command to invoke FunnelWeb proper. Discussion of the command
shell is deferred until later.
<P>
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