Hi,
[EMAIL PROTECTED] writes:
> I'm a little confused. The Wikipedia entry on guile has a vague statement
> about
> how guile can't do tail call optimization in functions that use C
> code.
First, we have to differentiate between tail call and _recursive tail
call---one usually cares more about the latter. Recursive tail calls
are always optimized in Scheme code, as mandated by R5RS (Section 3.5).
For example:
(let loop ((x 10))
(if (<= x 0)
#t
(loop (1+ x))))
Guile optimizes the tail-recursive call to `loop', so iterations of the
above loop do not consume any additional stack space.
Now, non-recursive tail calls certainly be optimized when the called
function is implemented in C. For instance:
(define (foo x)
(1+ x))
Here, `1+' is implemented in C, so the call to `1+' is not
tail-optimized (i.e., it consumes additional stack space). Hmm,
actually, if the C compiler used to compile Guile implements tail-call
optimization, then even such code might be tail-optimized.
I'm not sure whether tail calls to Scheme-implemented procedures are
optimized.
Anyway, the important point is that Guile does optimize tail-recursive
calls, fortunately.
> Wikipedia also says that guile has difficulties with call/cc, and I assume
> this
> is a similar issue, calling a continuation that was captured in scheme code
> that was called from a different C function than the currently running scheme
> code. Right? (confusing sentence, I know!)
AFAIK `call/cc' works "as expected" in Guile. The only problem is that
it is inefficient because the whole call stack has to be copied, as
mentioned in the manual.
Thanks,
Ludovic.
_______________________________________________
Guile-user mailing list
Guile-user@gnu.org
http://lists.gnu.org/mailman/listinfo/guile-user
