Just Programming
Everytime you change a language, you end up with a slighly different balance of features. Sometimes small language changes make for large balance changes.
In my recent argument with the guy on ExtremePerl, he said that he can learn and do everything he'll ever need in Perl. He said that if he had to write his own Logic Programming system in Perl, that was fine with him. He says it's because because he has such a huge investment in Perl that he doesn't want to take the time to learn other languages. If he wanted features from other languages, he would get them by reimplementing or emulating features from other languages in Perl.
But wait, is Perl purely functional? Is Perl logic programming?
from #perl6:
<Juerd> Let's found programmeria!
<Juerd> Coderia I mean
<Juerd> Or all move to Poland and rename it to Perlland. It already has the correct country extension.
<shapr> Juerd: but, I think programming is not limited to Perl, Haskell, or any one language.
<Juerd> shapr: Perl 6 is every language, so that's not a problem.
Realistically speaking, it's about identity. (see E-Prime on Ward's Wiki)
I say that languages do not have an identity, they have a description.
When you add new features to Perl, is it still Perl?
What if I removed referential transparency from Haskell? Is it still Haskell?
What if I modify Perl so that it uses prefix notation and only parentheses, not brackets or braces? Is that still Perl?
It's all just programming. Juerd is right, Perl 6 is in every language, just like every language is in every other language.