So far, this is the essence of continuation-passing style. Baker's novel idea is to use the C call stack for the Scheme heap. Hence, normal C stack operations such as automatic variable creation, variable-sized array allocation, and so on can be used. When the stack fills up (that is, the stack pointer reaches the top of the stack), a garbage collection can be initiated. The design used is a copying garbage collector originally devised by C. J. Cheney, which copies all live continuations and other live objects to the heap. Despite this, the C code does not copy C stack frames, only Scheme objects, so it does not require knowledge of the C implementation.