Wouldn't in_list be faster if it broke out early, instead of comparing all the items and then coercing to boolean? Something like

sub in_list { ( $_ eq $_[0] ) && return 1 for @_[ 1 .. $#_ ]; undef;}
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Though personally I'd go with the less compact, but more readable

sub in_list {
  for (@_[ 1 .. $#_ ]){
    return 1 if $_ eq $_[0];
  }
  undef;
}
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Since if it's going to be a sub anyway, you might as well make it a little easier to read.