On Sun, Sep 30, 2018 at 04:02:15AM -0700, ToddAndMargo wrote: : Hi All, : : https://docs.perl6.org/routine/join#(List)_routine_join : : method join(List:D: $separator --> Str:D) : : $ p6 'say (1, <a b c>).join("|");' : 1|a b c : : : It states in the manual that this will happen. : : Questions: : : 1) why?
Because an invocant is only one thing. In this case, it's a List of exactly two things: a 1 and a sublist of <a b c>. And you since passed .join only two things to stringify and join, it stringified the 1 and then it stringified the <a b c>, and then it joined those two things, just as you asked it to. A deeper "why" is that Perl 6 doesn't autoflatten sublists unless you explicitly ask it to, so you'd need to put |<a b c> to "slip" the sublist into the outer list, or use flat(). : 2) where in the method definition does it state : this will happen? It's not in the method definition, and it doesn't belong in the method definition. It's in the definition of how Perl 6 works at a fundamental level. We're not going to document every list argument in Perl 6 to say that it *doesn't* work like in Perl 5. : 3) why does this work? : $ p6 'join( "|", <1 2 3>).say;' : 1|2|3 Because functions can take multiple arguments, and so the signature of the join function is allowed (and required) to use a comma to separate those arguments. This is not the same comma that creates the general list above. Functions often cheat with their commas, especially functions that were borrowed from Perl 5, which cheats on most of its commas and doesn't really understand nested lists at all without explicit references. The deeper and/or shallower reason is that a Perl 5 programmer will expect the join function to work that way, and even expect the slurpy argument to autoflatten, which it does for old time's sake, and because it seems to be a useful DWIM for this particular string-based function. The functions that flatten their slurpy (like join) are explicitly marked with * on that argument in the signature. So it's still true that we flatten only explicitly in Perl 6, but that explicit mark is in the that pesky signature you gotta get your brain around someday. In short, the method form is optimized for people who understand nested lists and want them to to stay nested by default, while the function form is optimized for, er, the typical Perl 5 programmer who expects random list flattening in various places. Larry
