I'm puzzled (in an idle sort of way) as to why print for "1" .. "-1"; doesn't output the numbers 1 through to 99.

That is indeed quite strange, and I can't make sense of it at the moment... seems like a bug to me.

$ perl -wMstrict -MData::Dump -e' dd "0".."-1" '
(0 .. 99)
$ perl -wMstrict -MData::Dump -e' dd "1".."-1" '
()
$ perl -wMstrict -MData::Dump -e' dd "01".."-1" '
("01", "02", "03", "04", "05", "06", "07", "08", "09", 10 .. 99)
$ perl -wMstrict -MData::Dump -e' dd "90".."-1" '
()
$ perl -wMstrict -MData::Dump -e' dd "1".."xx" '
(1 .. 99)
$ perl -wMstrict -MData::Dump -e' dd "11".."xx" '
(11 .. 99)
$ perl -wMstrict -MData::Dump -e' dd "90".."xx" '
(90 .. 99)
$ perl -wMstrict -MData::Dump -e' dd "-1".."xx" '
-1
$ perl -wMstrict -MData::Dump -e' dd "0".." -1 " '
(0 .. 9999)
$ perl -wMstrict -MData::Dump -e' dd " 0 ".." -1 " '
()
$ perl -wMstrict -MData::Dump -e' dd " 11 ".." -1 " '
()
$ perl -wMstrict -MData::Dump -e' dd "0.0".."-1.0" '
"0.0"
$ perl -wMstrict -MData::Dump -e' dd " 0.0 ".." -1.0 " '
()
$ perl -wMstrict -MData::Dump -e' dd "0.0".." 1.0 " '
"0.0"
$ perl -wMstrict -MData::Dump -e' dd " 0.0 ".."1.0" '
(0, 1)

[download]

Maybe there's some kind of heuristic going wrong... for example, maybe the intention is that if both sides looks_like_number, then treat them as numbers instead of strings - but several of the cases above don't work like that. I dunno at the moment, this may need some digging in the sources. (I ran a bisect earlier, and it seems that at least the "1".."-1" case has always returned the empty list.)

Update: Reported as Bug #133695

Update 2019-08-27: See this node, which documents the behavior, as well as the change in the behavior as of Perl v5.32.

In reply to Re^3: curious behavior: why does it do this? by haukex
in thread curious behavior: why does it do this? by perl-diddler

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