Didn't know you wanted that. OK. New version (72 chars)

sub l{
my($s,$t)=@_;sub{($s=($s.(((my$x=$s+$t)=~y/1/1/d)%9%2)))=~s/5(.)/5/;$1
+}
}
 $x=l("50101","0022");print ($x->(),$x->(),$x->(),$x->());
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