Shiro Kawai wrote: > There's another point, though. There are two camps in Scheme > implementations regarding how to give the "fallback" value, both have > their own ground. If srfi-44 gives a convincing rationale for thunk > approach, and becomes widely spread, it may be possible that > eventually the convention of giving fallback value converges to thunk > approach. I've been thinking about this, and I'd rather raise an exception than provide a failure thunk. SRFI-34 defines exceptions, and SRFI-35 style conditions could provide information about the failure. It seems to me that a language with sophisticated support for continuations should take advantage of that in failure interfaces. It also simplifies call interfaces, since you don't ever need to distinguish, "Is this procedure a thunk or a collection datum?" Unfortunately, SRFI-34 isn't quite implementable on some Schemes. For example, PLT provides a RAISE primitive which is *almost* compatible with SRFI-34, which means that it's tough to replace -- you can't implement SRFI-44 with PLT RAISE, and existing code relies on the PLT version, causing interoperability problems. -- Bradd W. Szonye http://www.szonye.com/bradd
