var p_arr = alloc(size_of(array[int, 3]))
Above is incorrect syntax
Do
var p_arr = alloc sizeof(array[3, int])
Also [pointer arithmetic post](https://forum.nim-lang.org/t/1188#7366) should
be helpful
When you `alloc` something, it'll be put in heap, and untracked, so you need to
call `realloc` when you done with it.
If you're going to have a different thread, use shared variant like
`allocShared` and `reallocShared`
