suzanne.soy/racket
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

doc: fill gaps in spec for expt

Browse Source 
There's no good answer for `expt` in the vicinity of `(expt 0 0)`, and
I went in circles trying to redecide how things should work. Given
that RnRS defines `(expt 0 0)` to be 1, though, the status quo seems
as good as anything.
This commit is contained in:
Matthew Flatt 2019-01-17 16:49:16 -07:00
parent f5babc4246
commit 4ccbd7fcad
2 changed files with 35 additions and 20 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

54
pkgs/racket-doc/scribblings/reference/numbers.scrbl
View File

@ -549,16 +549,30 @@ Returns @racket[z] raised to the power of @racket[w].
If @racket[w] is
exact @racket[0], the result is exact @racket[1].
If @racket[w] is @racket[0.0] or @racket[-0.0] and @racket[z] is a @tech{real number}, the
If @racket[w] is @racket[0.0] or @racket[-0.0] and @racket[z] is a @tech{real number}
other than exact @racket[1] or @racket[0], the
result is @racket[1.0] (even if @racket[z] is @racket[+nan.0]).
If @racket[z] is exact @racket[1], the result is exact @racket[1].
If @racket[z] is @racket[1.0] and @racket[w] is a @tech{real number}, the
result is @racket[1.0] (even if @racket[w] is @racket[+nan.0]).
If @racket[z] is
exact @racket[0] and @racket[w] is negative, the
@exnraise[exn:fail:contract:divide-by-zero].
If @racket[z] is exact @racket[0], the result is as follows:
@;
@itemlist[#:style 'compact
@item{@racket[w] is exact @racket[0] --- result is @racket[1]}
@item{@racket[w] is @racket[0.0] or @racket[-0.0] --- result is @racket[1.0]}
@item{real part of @racket[w] is negative --- the @exnraise[exn:fail:contract:divide-by-zero]}
@item{@racket[w] is nonreal with a nonpositive real part --- the @exnraise[exn:fail:contract:divide-by-zero]}
@item{@racket[w] is @racket[+nan.0] --- result is @racket[+nan.0]}
@item{otherwise --- result is @racket[0]}
]
Further special cases when @racket[w] is a @tech{real number}:
@margin-note*{These special cases correspond to @tt{pow} in C99 @cite["C99"],
@ -569,45 +583,45 @@ integer.}
@item{@racket[(expt 0.0 w)]:
@itemlist[#:style 'compact
@item{@racket[w] is negative --- @racket[+inf.0]}
@item{@racket[w] is positive --- @racket[0.0]}]}
@item{@racket[w] is negative --- result is @racket[+inf.0]}
@item{@racket[w] is positive --- result is @racket[0.0]}]}
@item{@racket[(expt -0.0 w)]:
@itemlist[#:style 'compact
@item{@racket[w] is negative:
@itemlist[#:style 'compact
@item{@racket[w] is an odd integer --- @racket[-inf.0]}
@item{@racket[w] otherwise rational --- @racket[+inf.0]}]}
@item{@racket[w] is an odd integer --- result is @racket[-inf.0]}
@item{@racket[w] otherwise rational --- result is @racket[+inf.0]}]}
@item{@racket[w] is positive:
@itemlist[#:style 'compact
@item{@racket[w] is an odd integer --- @racket[-0.0]}
@item{@racket[w] otherwise rational --- @racket[+0.0]}]}]}
@item{@racket[w] is an odd integer --- result is @racket[-0.0]}
@item{@racket[w] otherwise rational --- result is @racket[+0.0]}]}]}
@item{@racket[(expt z -inf.0)] for positive @racket[z]:
@itemlist[#:style 'compact
@item{@racket[z] is less than @racket[1.0] --- @racket[+inf.0]}
@item{@racket[z] is greater than @racket[1.0] --- @racket[+0.0]}]}
@item{@racket[z] is less than @racket[1.0] --- result is @racket[+inf.0]}
@item{@racket[z] is greater than @racket[1.0] --- result is @racket[+0.0]}]}
@item{@racket[(expt z +inf.0)] for positive @racket[z]:
@itemlist[#:style 'compact
@item{@racket[z] is less than @racket[1.0] --- @racket[+0.0]}
@item{@racket[z] is greater than @racket[1.0] --- @racket[+inf.0]}]}
@item{@racket[z] is less than @racket[1.0] --- result is @racket[+0.0]}
@item{@racket[z] is greater than @racket[1.0] --- result is @racket[+inf.0]}]}
@item{@racket[(expt -inf.0 w)] for integer @racket[w]:
@itemlist[#:style 'compact
@item{@racket[w] is negative:
@itemlist[#:style 'compact
@item{@racket[w] is odd --- @racket[-0.0]}
@item{@racket[w] is even --- @racket[+0.0]}]}
@item{@racket[w] is odd --- result is @racket[-0.0]}
@item{@racket[w] is even --- result is @racket[+0.0]}]}
@item{@racket[w] is positive:
@itemlist[#:style 'compact
@item{@racket[w] is odd --- @racket[-inf.0]}
@item{@racket[w] is even --- @racket[+inf.0]}]}]}
@item{@racket[w] is odd --- result is @racket[-inf.0]}
@item{@racket[w] is even --- result is @racket[+inf.0]}]}]}
@item{@racket[(expt +inf.0 w)]:
@itemlist[#:style 'compact
@item{@racket[w] is negative --- @racket[+0.0]}
@item{@racket[w] is positive --- @racket[+inf.0]}]}
@item{@racket[w] is negative --- result is @racket[+0.0]}
@item{@racket[w] is positive --- result is @racket[+inf.0]}]}
]
@mz-examples[(expt 2 3) (expt 4 0.5) (expt +inf.0 0)]}

1
pkgs/racket-test-core/tests/racket/number.rktl
View File

@ -1912,6 +1912,7 @@
(err/rt-test (expt 0 0.0+2i) exn:fail:contract:divide-by-zero?)
(err/rt-test (expt 0 -0.0+2i) exn:fail:contract:divide-by-zero?)
(err/rt-test (expt 0 0+0.0i) exn:fail:contract:divide-by-zero?)
(err/rt-test (expt 0 +nan.0+1.0i) exn:fail:contract:divide-by-zero?)
(err/rt-test (expt 'a 0))
(err/rt-test (expt 'a 1))