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<P><FONT SIZE="5">2.5 Parameterized Macros</FONT><BR>



<P>No self-respecting macro preprocessor would be complete
without some form of macro parameterization, and FunnelWeb
is no exception. FunnelWeb allows each macro to have from
zero to nine formal parameters
named <SAMP>@1</SAMP>, <SAMP>@2</SAMP>,
<SAMP>@3</SAMP>, <SAMP>@4</SAMP>, <SAMP>@5</SAMP>, <SAMP>@6</SAMP>,
<SAMP>@7</SAMP>, <SAMP>@8</SAMP>, and <SAMP>@9</SAMP>.

<P>To define a macro with one or more parameters, insert a
formal parameter list just after
the macro name in the macro definition. Because macro
parameters have fixed names
(<SAMP>@1</SAMP>...<SAMP>@9</SAMP>), there is no need to
specify the names of formal parameters in the formal
parameter list. All that need be conveyed is how many
parameters the macro has. Here is an example of the
definition of a macro having three parameters:

<P>
<PRE>
@$@&lt;While loop@&gt;@(@3@)@M==@{@-
@1
while (@2)
  {
   @3
  }
@}
</PRE>

<P>To call a parameterized macro, an actual
parameter list must be supplied
that contains exactly the same number of actual parameters
as there are formal parameters in the definition of the
macro being called. An actual parameter list is delimited by
<SAMP>@(</SAMP> and <SAMP>@)</SAMP>, and
parameters are <I>separated</I>&nbsp; by
<SAMP>@,</SAMP>. The actual parameters themselves
are general FunnelWeb expressions (see the
<A HREF="../reference/index.html"
 TARGET="funnelwebreference"
 onClick="window.open('','funnelwebreference','location,status,menubar,scrollbars,resizable',false).focus(); return true;"
>FunnelWeb Reference Manual</A> for the exact syntax) and can
be inserted into the list directly or can be delimited by
<SAMP>@"</SAMP> so as to allow some white space to
assist in formatting the actual parameters. Here are some
examples of calls of the <SAMP>While loop</SAMP> macro defined
above.

<P>
<PRE>
@! First form of actual parameters
@! without whitespace and double quotes.
@&lt;While loop@&gt;@(@-
x=1;@,x&lt;=10@,printf("X=%u\n",x);@)

@! Second form of actual parameters. The double
@! quotes allow non-active whitespace that helps
@! to lay out the actual parameters neatly. This
@! call is functionally identical to the one above.
@&lt;While loop@&gt;@(
   @"x:=1;@" @,
   @"x&lt;=10@" @,
   @"printf("X=%u\n",x);@" @)

@! The two forms can be mixed in a single call.
@&lt;While loop@&gt;@(x=1;@,x&lt;=10@,
              @"printf("X=%u\n",x);@" @)
</PRE>

<P>A few rules about parameterized macros are worth
mentioning. Macros that do not have any parameters must have
no formal or actual parameter lists. Additive macros can have parameters, but the
formal parameter list must appear in the first definition
part only.

<P>Here is another example of the use of parameterized
macros. This time, parameters and macro calls are used in a
FunnelWeb input file that constructs an O(n)
representation of a song whose full size is O(n^2) in the number n of
unique lines.

<P>
<PRE>
@O@&lt;Twelve_bugs.txt@&gt;==@{@-
The Twelve Bugs of Christmas
----------------------------
@&lt;Verse@&gt;@(@"first@"    @,@&lt;1@&gt;@)
@&lt;Verse@&gt;@(@"second@"   @,@&lt;2@&gt;@)
@&lt;Verse@&gt;@(@"third@"    @,@&lt;3@&gt;@)
@&lt;Verse@&gt;@(@"fourth@"   @,@&lt;4@&gt;@)
@&lt;Verse@&gt;@(@"fifth@"    @,@&lt;5@&gt;@)
@&lt;Verse@&gt;@(@"sixth@"    @,@&lt;6@&gt;@)
@&lt;Verse@&gt;@(@"seventh@"  @,@&lt;7@&gt;@)
@&lt;Verse@&gt;@(@"eighth@"   @,@&lt;8@&gt;@)
@&lt;Verse@&gt;@(@"ninth@"    @,@&lt;9@&gt;@)
@&lt;Verse@&gt;@(@"tenth@"    @,@&lt;A@&gt;@)
@&lt;Verse@&gt;@(@"eleventh@" @,@&lt;B@&gt;@)
@&lt;Verse@&gt;@(@"twelfth@"  @,@&lt;C@&gt;@)

This song appeared in the internet newsgroup
rec.humor.funny on 24-Dec-1991. It was contributed
by Pat Scannell (scannell@@darkstar.ma30.bull.com).
@}

@$@&lt;Verse@&gt;@(@2@)@M==@{@-
For the @1 bug of Christmas, my manager said to me
     @2
@}

@$@&lt;1@&gt;@M==@{@-
See if they can do it again.@}
@$@&lt;2@&gt;@M==@{@-
Ask them how they did it and@+@&lt;1@&gt;@}
@$@&lt;3@&gt;@M==@{@-
Try to reproduce it@+@&lt;2@&gt;@}
@$@&lt;4@&gt;@M==@{@-
Run with the debugger@+@&lt;3@&gt;@}
@$@&lt;5@&gt;@M==@{@-
Ask for a dump@+@&lt;4@&gt;@}
@$@&lt;6@&gt;@M==@{@-
Reinstall the software@+@&lt;5@&gt;@}
@$@&lt;7@&gt;@M==@{@-
Say they need an upgrade@+@&lt;6@&gt;@}
@$@&lt;8@&gt;@M==@{@-
Find a way around it@+@&lt;7@&gt;@}
@$@&lt;9@&gt;@M==@{@-
Blame it on the hardware@+@&lt;8@&gt;@}
@$@&lt;A@&gt;@M==@{@-
Change the documentation@+@&lt;9@&gt;@}
@$@&lt;B@&gt;@M==@{@-
Say it's not supported@+@&lt;A@&gt;@}
@$@&lt;C@&gt;@M==@{@-
Tell them it's a feature@+@&lt;B@&gt;@}
</PRE>


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