C:\test>perl -MO=Deparse -le"use constant SNaN => unpack'd', pack'Q',0x7ff0000000000001; print SNaN; if( SNaN != SNaN ) { print 'here'; }"
BEGIN { $/ = "\n"; $\ = "\n"; }
use constant ('SNaN', unpack('d', pack('Q', 9218868437227405313)));
print unpack("F", pack("h*", "1000000000000ff7"));
do {
    print 'here'
};
-e syntax OK

C:\test>perl -MO=Deparse -le"use constant SNaN => unpack'd', pack'Q', 0x7ff0000000000001; print SNaN; if( SNaN == SNaN ) { print 'here'; }"
BEGIN { $/ = "\n"; $\ = "\n"; }
use constant ('SNaN', unpack('d', pack('Q', 9218868437227405313)));
print unpack("F", pack("h*", "1000000000000ff7"));
'???';
-e syntax OK