Making a signature accept a list of Pairs

[FCO]

https://colabti.org/irclogger/irclogger_log/raku?date=2020-04-20#l387

m: sub a([$a]) { dd $a }; a [1]; a [1 => 2]
23:35 C<camelia> combined, experimental evalbot rakudo-moar b0a720cb6: OUTPUT: «1␤Too few positionals passed to 'a'; expected 1 argument but got 0 in sub-signature␤  in sub a at <tmp> line 1␤  in block <unit> at <tmp> line 1␤␤»

[jnthn]

I think having List.Capture automatically promote any Pair in the list into a named argument was probably a mistake (one of mine too, maybe I need to borrow rule 2 for a moment... :-))

The remaining question is how we can change this without inflicting breakage. There's two scenarios:

1. We try and change it. We blin it. We find nothing at all depended on the current semantics. We say, eh, cheating is technique, and just change it.
2. We start passing a named argument to .Capture in signature binding to indicate old vs. new semantics, depending on the language version the signature shows up in.

[jnthn]

Ah, and I hereby delegate the research to find out which of 1 or 2 we have to do, to somebody enthusiastic about it. :-)