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>Date: 26 Apr 1986 10:33 EST (Sat)
>From: Bill Rozas <JINX%OZ.AI.MIT.EDU%xx.lcs.mit.edu@csnet-relay>
> -- I like warning messages for things like (MAKE-VECTOR 0 exp) more
> than you do. We can probably agree to provide declarations so you
> won't refuse to buy my system!
>I agree with JAR. I think that (MAKE-VECTOR 0 exp) is reasonable and
>no error (warning) message should be given. I don't understand why
>you object to it. Why not warn about reversing a list with less than 2
I'm not objecting, just asking questions to clarify JAR's position and
to elicit comments from others with strong opinions. Let's see if I
can clarify both mine and yours:
-- I agree that (MAKE-VECTOR EXP1 EXP2) shouldn't be an error or
cause a warning at runtime should EXP1 evaluate to zero. I'm talking
about compile-time warnings (e.g. for a COMPILE-FILE) when EXP1 is a
literal zero. I oppose most, perhaps all, warnings during evaluation.
Sorry I wasn't more explicit -- I tend to think in terms of separate
compilation and I'm sure many of you are thinking primarily in terms
-- Likewise, (REVERSE EXP3) obviously shouldn't cause a warning when
EXP3 evaluates to a list with fewer than two elements. But a
compile-time warning about (REVERSE '(A)) might be helpful (if it
weren't so unlikely!).
There's no real debate here. If I were to report `warnings,' as
opposed to actual `errors,' I'd do it only in a compilation mode where
they wouldn't be confused with the runtime behavior of the program and
only if the user asked for them by setting a flag. This is a
development environment issue, not a language issue.
> -- We agree that (ELSE) is a no-no and that (COND) and (COND (ELSE exp))
> are valid.
> -- I feel that (BEGIN) should have the same meaning as (COND), but I
> won't push the point.
>I don't like this. Unfortunately JAR did not give me choice c (status
>quo, where (COND (ELSE ...)) is legal, but (COND) is not), which I
>like best. I object pretty strongly to (BEGIN) and somewhat less
>strongly to (COND). The usual rationale is that it makes macros
>easier to write, but this is just laziness of the same sort as using
>(cdr (assq <something> <some-list>)) in a Lisp where (cdr '()) -> '().
>(COND (ELSE ...)) although silly has a clear meaning (unless the ELSE
>clause is empty, which should be an error, but we agree on this).
Actually, JINX and I seem to agree that (BEGIN) and (COND) are equally
meaningless. I offer to allow (COND) but feel (BEGIN) makes as much
sense. If there's a consensus against (COND), then I'm even happier.
I'm not all that motivated by wanting to write lazy macros or program-
generating programs for reasons similar to JINX's.
- From: Bill Rozas <JINX%OZ.AI.MIT.EDU@xx.lcs.mit.edu>