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UPDATE

please see my other post here: Re: discussion: What should split( /PATTERN/, EXPR, 0 ) return better? (LIMIT is consistent! ) which makes most of the following reasoning obsolete (the code still works)

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Again I was struggling to understand what your question is (or rather your meditation).

Yes I agree that it's not very orthogonal, if LIMIT > 0 is a count and LIMIT == 0 rather means undef like in "No Limit" .*

I don't see where this concept stems from, probably some sed or awk semantic, (probably because undef is missing there ?)²

But I agree with afoken that it's too late to change it.

Anyway I would never have tried to solve it that way, rather

  DB<1> $str = join " ", 1..5

  DB<2> for $k (0..6) { my $sum=0; $sum+= $_ for (split ' ', $str)[0..
+$k-1] ; print "$sum\n";}
0
1
3
6
10
15
15
[download]

or rather

  DB<6> @split = (split ' ', $str)

  DB<7> for $k (0..6) { my $sum=0; $sum+= $_ for @split[0..$k-1]; prin
+t "$sum\n";}
0
1
3
6
10
15
15
[download]

update

*) and you shouldn't forget that LIMIT =-1 has even one more non-count meaning

²) couldn't find similarities in awk or sed, but the reason is most probably that 0 and undef are both false in Perl, and the designers wanted to keep the symmetry.