Carp requires writing bindings to call C functions or use types. Additionally, code modification isn't possible in Carp.
When I say seamless, I'm going for as close as possible, I.e. it should feel even easier to use C from Cakelisp than from C itself. The build system especially makes this possible.
As someone who works on Carp, it seems we're going for one level of abstraction higher than what this is aiming for. It's pretty easy to do C interop but the goal isn't to write "C in S-expressions".
When I say seamless, I'm going for as close as possible, I.e. it should feel even easier to use C from Cakelisp than from C itself. The build system especially makes this possible.