#!/usr/bin/perl --
use Devel::Peek qw/ Dump /;
select STDERR;
print "\n\$ARGV\n";                  Dump( $ARGV );
print "\nundef\n";                   Dump( undef );
print "\n!!0 PL_sv_no\n";            Dump( !!0 );
print "\ndefined undef\n";           Dump( defined undef );
print "\n!!1 PL_sv_yes\n";           Dump( !!1 );
print "\ndefined defined undef\n";   Dump( defined defined undef );
__END__
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$ARGV
SV = NULL(0x0) at 0x99b90c
  REFCNT = 1
  FLAGS = ()

undef
SV = NULL(0x0) at 0x3f4cc0
  REFCNT = 2147482895
  FLAGS = (READONLY)

!!0 PL_sv_no
SV = PVNV(0x3f7f84) at 0x3f4968
  REFCNT = 2147483646
  FLAGS = (PADTMP,IOK,NOK,POK,READONLY,pIOK,pNOK,pPOK)
  IV = 0
  NV = 0
  PV = 0x3f405c ""\0
  CUR = 0
  LEN = 12

defined undef
SV = PVNV(0x3f7f84) at 0x3f4968
  REFCNT = 2147483646
  FLAGS = (PADTMP,IOK,NOK,POK,READONLY,pIOK,pNOK,pPOK)
  IV = 0
  NV = 0
  PV = 0x3f405c ""\0
  CUR = 0
  LEN = 12

!!1 PL_sv_yes
SV = PVNV(0x3f7f9c) at 0x3f4978
  REFCNT = 2147483643
  FLAGS = (PADTMP,IOK,NOK,POK,READONLY,pIOK,pNOK,pPOK)
  IV = 1
  NV = 1
  PV = 0x3f8e7c "1"\0
  CUR = 1
  LEN = 12

defined defined undef
SV = PVNV(0x3f7f9c) at 0x3f4978
  REFCNT = 2147483643
  FLAGS = (PADTMP,IOK,NOK,POK,READONLY,pIOK,pNOK,pPOK)
  IV = 1
  NV = 1
  PV = 0x3f8e7c "1"\0
  CUR = 1
  LEN = 12