On 11 Jul 2000, bernard URBAN wrote:
> # guile
> guile> (version)
> "1.4"
> guile> (expt 2 -1)
> ERROR: In procedure integer-expt:
> ERROR: Argument out of range: -1
> ABORT: (out-of-range)
> guile> ($expt 2 -1)
> 0.5
> guile>
>
> >From boot-9.scm:
> (define expt
> (let ((integer-expt integer-expt))
> (lambda (z1 z2)
> (cond ((exact? z2)
> (integer-expt z1 z2))
> ((and (real? z2) (real? z1) (>= z1 0))
> ($expt z1 z2))
> (else
> (exp (* z2 (log z1))))))))
The test for exactness if wrong here: Rationals (if supported) could
fulfill that predicate as well. I will apply the following patch:
diff -u -r1.208 boot-9.scm
--- boot-9.scm 2000/07/01 17:01:22 1.208
+++ boot-9.scm 2000/07/12 07:23:07
@@ -793,7 +793,7 @@
(define expt
(let ((integer-expt integer-expt))
(lambda (z1 z2)
- (cond ((exact? z2)
+ (cond ((and (integer? z2) (>= z2 0))
(integer-expt z1 z2))
((and (real? z2) (real? z1) (>= z1 0))
($expt z1 z2))
> I noticed also that list-tail does no longer accept a second negative
> argument. R5RS say it is an error if the list length is shorter
> than the second argument, but is silent for the negative case.
But the example implementation given in R5RS relies on the fact that the
parameter is positive or zero. Further, I can not think of any reasonable
behaviour for the case of negative indexes. Thus, IMO it is a bug fix
rather than a bug that negative indexes are not accepted.
Best regards
Dirk
