Re: continuation efficiency

[Thomas Bushnell, BSG]

Martin Grabmueller <address@hidden> writes:

> call/cc does a full copy of the machine stack, to be able to install
> it again when the continuation is invoked.  This requires memory
> allocation and copying, which is a bit slow.
> 
> call/ec, on the other hand, does not need to preserve the stack, since
> it only allows calls upwards in the call chain.  Think of call/ec as
> throw/catch and you'll see.  So call/ec is less powerful, but faster
> (in Guile, other Schemes may vary).

This all depends on the *implementation*.  The original post implied
that call/ec was not a primitive.  If it is implemented as a wrapper
around call/cc, then how can it be more efficient?