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<TITLE>5.4 Fiddling With End of Lines</TITLE>
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<P><FONT SIZE="5">5.4 Fiddling With End of Lines</FONT><BR>
<P>One of the fiddly aspects of programming with
FunnelWeb is coping with end of lines. If you want your
product file to be well indented without multiple blank
lines or code run-ons, you have to spend a little time
working out how the end of line markers get moved around.
<P>The rule to remember is that, disregarding the
effects of special sequences within a macro body,
<I>the body of a macro consists of exactly the text
between the opening <SAMP>@{</SAMP> and the closing
<SAMP>@}</SAMP></I> . This text includes end of line markers.
<P>If for example you call a macro in a sequence of
code...
<P>
<PRE>
while the_walrus_is_sleepy do
begin
writeln('zzzzzzz');
@<Wake up the walrus@>
writeln('Umpharumpha...');
end;
</PRE>
<P>where <SAMP><wake up the walrus></SAMP> is defined
as follows
<P>
<PRE>
@$@<Wake up the walrus@>==@{
wake_up_the_walrus(the_walrus);
@}
</PRE>
<P>then when <SAMP><Wake up the walrus></SAMP> is
expanded you will get
<P>
<PRE>
while the_walrus_is_sleepy do
begin
writeln("zzzzzzz");
wake_up_the_walrus(the_walrus);
writeln("Umpharumpha...");
end;
</PRE>
<P>The blank lines were introduced by the end on line
markers included in the definition of <SAMP><Wake up
the walrus></SAMP>. A good solution to this problem is to
suppress the end of line markers by defining the macro as
follows
<P>
<PRE>
@$@<Wake up the walrus@>==@{@-
wake_up_the_walrus(the_walrus);@}
</PRE>
<P>This is the usual form of macro definitions in
FunnelWeb files.
<P>In additive macros, this format does not work properly
because the end of line that is suppressed by the trailing
<SAMP>@}</SAMP> does not get replaced by the end of line at
the end of the macro invocation. For example the definition
<P>
<PRE>
@$@<Wake up the walrus@>+=@{@-
wake_up_the_walrus_once(the_walrus);@}
</PRE>
<P>later followed by
<P>
<PRE>
@$@<Wake up the walrus@>+=@{@-
wake_up_the_walrus_again(the_walrus);@}
</PRE>
<P>is equivalent to the single definition
<P>
<PRE>
@$@<Wake up the walrus@>==@{@-
wake_up_the_walrus_once(the_walrus);@-
wake_up_the_walrus_again(the_walrus);@}
</PRE>
<P>Putting the trailing <SAMP>@}</SAMP> on a new line at
the end of the macro (except for the last definition part)
solves the problem.
<P>
<PRE>
@$@<Wake up the walrus@>+=@{@-
wake_up_the_walrus_once(the_walrus);
@}
</PRE>
<P>later followed by
<P>
<PRE>
@$@<Wake up the walrus@>+=@{@-
wake_up_the_walrus_again(the_walrus);@}
</PRE>
<P>is equivalent to the single definition
<P>
<PRE>
@$@<Wake up the walrus@>==@{@-
wake_up_the_walrus_once(the_walrus);
wake_up_the_walrus_again(the_walrus);@}
</PRE>
<P>Managing end of line markers is tricky, but once you
establish a convention for coping with them, the problem
disappears into the background.
<P>
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