My list (the list may have items on it for which there are "Perl" modules doing the thing mentioned, but typically such modules contain large parts of C and/or XS code - which isn't Perl).
- Number crunching. Accessing the value of a number requires following at least two pointers, plus some additional overhead to check to see whether the numeric value is correct.
- Anything that requires to be CPU/register/memory/cache friendly. The flexibility of Perl comes with a price, and that's paid with CPU and memory.
- Anything that requires a small footprint in disk space. Compiling C programs with the right compiler can give you programs of just a few k, meaning you can pack a lot of them on a floppy. There's no way to install perl on a floppy.
- Direct memory access, due to the lack of pointers.
- Locking regions of files instead of the entire file.
- Calling kernel hooks.
- Many things for which there are special purpose languages (music, vector images, etc)
- Real time programming
- Threads
- OO
And all other things I forgot.
Abigail