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   print VMACRO "#include \"$htfile\"\n";
   foreach $func (sort keys %VVar)
    {
     if (!exists $Exclude{$func})
      {
       print VFUNC $VVar{$func};
       print VMACRO "#define $func (*${name}ptr->V_$func)\n"
      }
    }
   foreach $func (sort keys %VFunc)
    {
     if (!exists $Exclude{$func})
      {
       print VFUNC $VFunc{$func};
       print VMACRO "#define $func (*${name}ptr->V_$func)\n"
      }
    }
   print VMACRO "#endif /* _${gard}_VM */\n";
   close(VMACRO);
   print VFUNC  "#endif /* _$gard */\n";
   close(VFUNC); # Close this last - Makefile dependancy
  }
}

foreach (<tk*Tab.c>)
 {
  Exclude($_);
 }

foreach (@ARGV)
 {
  Vfunc($_);
 }

__END__

=head1 NAME

mkVFunc - Support for "nested" dynamic loading

=head1 SYNOPSIS

 mkVFunc xxx.h

=head1 DESCRIPTION

B<perl/Tk> is designed so that B<Tk> can be dynamically loaded 'on top of'
perl. That is the easy bit. What it also does is allow Tk::Xxxx to be
dynamically loaded 'on top of' the B<perl/Tk> composite. Thus when
you 'require Tk::HList' the shared object F<.../HList.so> needs to be
able to call functions defined in perl I<and> functions defined in loadable
.../Tk.so . Now functions in 'base executable' are a well known problem,
and are solved by DynaLoader. However most of dynamic loading schemes
cannot handle one loadable calling another loadable.

Thus what Tk does is build a table of functions that should be callable.
This table is auto-generated from the .h file by looking for
'extern' (and EXTERN which is #defined to 'extern').
Thus any function marked as 'extern' is 'referenced' by the table.
The address of the table is then stored in a perl variable when Tk is loaded.
When HList is loaded it looks in the perl variable (via functions
in perl - the 'base executable') to get the address of the table.

The same utility that builds the table also builds a set of #define's.
HList.c (and any other .c files which comprise HList) #include these
#define's. So that

  Tk_SomeFunc(x,y,z)

Is actually compiled as

  (*TkVptr->V_Tk_SomeFunc)(x,y,z)

Where Tk_ptr is pointer to the table.

See:

 Tk-b*/pTk/mkVFunc - perl script that produces tables
          /tk.h        - basis from which table is generated
          /tk.m        - #define's to include in sub-extension
          /tk_f.h      - #included both sides.
          /tk_f.c      - Actual table definition.
          /tk.t        - 'shared' set of macros which produce table
                         included in tk_f.c and tk_f.h
          /tkVMacro.h  - Wrapper to include *.m files

In addition to /tk* there are /tkInt*, /Lang* and /tix*

=cut