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<P><FONT SIZE="5">1.4 Diagnostics</FONT><BR>
<P>During execution, FunnelWeb proceeds cautiously with
each of its phases, only proceeding with the next phase if
the previous phase has been successful. This means that,
when debugging a FunnelWeb file, you may find that the
number of errors <I>increases</I> after you fix some of
them, as you will be exposing yourself to the next FunnelWeb
phase.
<P>FunnelWeb employs five levels of
diagnostics at different
levels of severity. Severity is defined in
terms of the level of activity at which the diagnostic
causes FunnelWeb to abort.
<P><BLOCKQUOTE><B>Warning:</B> A
warning does not cause FunnelWeb
to terminate or curtail its operation in any way, but serves
merely to warn the user of particular conditions that might
be symptomatic of deeper problems.</BLOCKQUOTE>
<P><BLOCKQUOTE><B>Error:</B> An error
causes FunnelWeb to terminate processing of the current
input file at the end of the current phase. For example, if
an error occurs during scanning, FunnelWeb will continue
scanning (and possibly generate further scanning
diagnostics), but will not invoke the parser.</BLOCKQUOTE>
<P><BLOCKQUOTE><B>Severe Error:</B> A
severe error (or "severe" for short) is the same as
an error except that FunnelWeb terminates the current phase
immediately.</BLOCKQUOTE>
<P><BLOCKQUOTE><B>Fatal Error:</B> A
fatal error causes FunnelWeb not only to terminate the
current phase and run immediately, but also to terminate
total FunnelWeb processing immediately. A severe error will
not cause a FunnelWeb script to terminate, but a fatal error
will. A fatal error causes FunnelWeb to return control to
the operating system.</BLOCKQUOTE>
<P><BLOCKQUOTE><B>Assertion
Error:</B> An assertion error
occurs if FunnelWeb detects an internal inconsistency, in
which case FunnelWeb terminates immediately and
ungracefully. Such an error can occur only if there are
bugs in FunnelWeb. With luck, such errors will be extremely
rare.</BLOCKQUOTE>
<P>FunnelWeb indicates the level of severity of each
diagnostic that it issues by starting each diagnostic either
with the full name of the severity level or with just the
first letter of the severity level followed by a colon.
<P>FunnelWeb conveys the presence or absence of
diagnostics at the operating system level by returning
<SAMP>EXIT_SUCCESS</SAMP> status if no
diagnostics occurred during the run and
<SAMP>EXIT_FAILURE</SAMP> status if one or more diagnostics
(including warnings) occurred during the run. (From
the symbols of the ANSI standard C library
<SAMP>stdlib.h</SAMP>. See <STRONG>[Kernighan88]</STRONG>, p.252.)
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