-Idirectory
            may  be  used  in  conjunction  with -P to tell the C preprocessor
            where to look for include  files.   By  default  /usr/include  and
            /usr/lib/perl are searched.

       -P   causes your script to be run through  the  C  preprocessor  before
            compilation  by  perl.   (Since  both  comments and cpp directives
            begin with the # character, you  should  avoid  starting  comments
            with  any  words  recognized  by  the C preprocessor such as "if",
            "else" or "define".)


##</code><code>##

#define ADD(x,y)  x + y

my $r = ADD( getPfromSomewhere(), getQfromSomewhere() );
...
my $s = ADD( geta(), getb() );

##</code><code>##

# 1 "macro.pl"
# 1 "<command-line>"
# 1 "/usr/include/stdc-predef.h" 1 3 4
# 30 "/usr/include/stdc-predef.h" 3 4
# 1 "/usr/include/x86_64-linux-gnu/bits/predefs.h" 1 3 4
# 31 "/usr/include/stdc-predef.h" 2 3 4
# 1 "<command-line>" 2
# 1 "macro.pl"


my $r = getPfromSomewhere() + getQfromSomewhere();
...
my $s = geta() + getb();