Perl-to-C compiler

Actually two of them.
One emits C code to rebuild Perl's parse tree and then restart the interpreter.
One emits C code that mimics Perl's parse tree. No interpreter.
Either way you're still dealing with Perl data structures (SV, AV, stash, etc) and Perl's internal functions.

If you want to learn how Perl works:

perl -MO=Terse program.plx perl -MO=Debug program.plx

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YAPC 2000: Stages of a Perl Programmer - 50