Vectors are very useful when accessing random positions in array. Lists are very inefficient for this because they need O(n) operations to access one item, whereas vectors only O(1).
1) Built-in C-interface
2) Native efficient compiler
3) Regular expressions
4) Built-in object system like CLOS
5) All data types, like hash tables and (CLOS?) objects, have their own text representation, so they can be read by the reader and properly printed.
6) Arc should have not only defmacro, but Scheme's define-syntax (defsyntax) too.
7) More functions for string parsing and printing.
