perl_changes.md

Differences from Perl 6 by design

In perl6, lookaround assertions have before and after on the wrong side of the leading to weird things like them both being backwards when both are used. For example in Perl 6:

# lookahead
say "foobar" ~~ / foo <?before bar> /; # foo
# lookbehind
say "foobar" ~~ / <?after foo> bar /; # bar
# both
say "foobarbaz" ~~ / <?after foo> bar <?before baz> /; # bar

I find this enormously confusing and it throws me every time because when I see before, I always interpret it backwards and I have to manually invert it to comprehend it. I'd invert it like so:

// lookahead
say "foobar" ~~ / foo <?after bar> /; # foo
// lookbehind
say "foobar" ~~ / <?before foo> bar /; # bar
// both
say "foobarbaz" ~~ / <?before foo> bar <?after baz> /; # bar