I think the standard has failed to be a lisp, and failed in the
Scheme tradition, if it does not permit viable non-standard
interpretations of programs which are divergent under the
standard (see my earlier post "Mathematical Foundations").
For example, suppose that a procedure which is not provably
terminating in a portable interpretation has the property that,
nevertheless, we can say that *if* it terminates, the type of
the return value is CHAR?. Further, suppose the procedure
is invoked in a context that is only strict in the type of the
return value.
Must R6RS prohibit an implementation from completing this
computation?
Before answering, please read "On Games and Numbers".
Regards,
-t
Arthur A. Gleckler wrote:
On Feb 24, 2007, at 4:54 PM, William D Clinger wrote:
Matthias Felleisen wrote:
2. Naturally I don't reject type systems per se but I think that a
serious
language definition shouldn't introduce such systems without
specifying
them. Otherwise a language/implementation will appear whimsical to
programmers.
The current draft already mandates hundreds of runtime
exceptions whose whimsical purpose is to make programs
that violate the requirements of the R6RS less likely
to run to completion. Why should that kind of whimsy
be limited to run time?
My only concern is that an error in one part of my program should not
prevent me from running another part of the program. The thing I most
dislike about most statically typed language implementations is that
they prevent me from testing a program that isn't yet completely
type-correct when I'm not even planning to invoke the broken part of
the program. I suppose that this suggestion only allows, but doesn't
require, compiler writers to signal errors it can detect at compile
time. Still, I'd rather not encourage this behavior if it makes it
impossible to run programs that are not yet completely correct.
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