There are some “Pure Perl” packages out there, certainly.   But if you’re getting a segmentation fault, you are definitely (directly or indirectly...) dealing with one that is not.

Many Perl packages consist partially or entirely of “wrappers for” existing libraries.   (e.g. XML::LibXML).   Others (YAML::Syck) do it for speed.   So, even though you as a Perl programmer are simply dealing with “a nice, well-behaved Perl package,” in the case of some packages there are lower-level calls being made under the hood.   The source-code of the package therefore consists, not only of Perl code, but also C/C++ code and the necessary “plumbing” needed to connect one to the other.   Just install the package in the usual way, and, presto, it all just happens.   It’s kind of like Laws and Sausages:   they work (well, sausages do, anyway), but you really don’t want to know how they’re made ...