[swift-evolution] [Proposal]: Free the '$' Symbol!

[Chris Lattner]

> On Jan 2, 2016, at 11:53 PM, Brent Royal-Gordon via swift-evolution <swift-evolution at swift.org> wrote:
> 
>> Swift currently does not allow operators to use $ - I assume because the grammar reserves it in one place: `implicit-parameter-name`.  I don't see why an entire class of identifiers has been eliminated, so I propose $ instead be reclassified as an `operator-character` so it can be used mixed in with other such characters, but prevents the introduction of `$Identifier`-style declarations that might conflict with implicit parameters.
> 
> I believe the reason you don't see any other $ variables is that they're reserved for the debugger and REPL.
> 
> 	brent at Brents-MacBook-Pro ~/D/Code> swift
> 	Welcome to Apple Swift version 2.1.1 (swiftlang-700.1.101.15 clang-700.1.81). Type :help for assistance.
> 	  1> "foo"
> 	$R0: String = "foo"
> 	  2> print($R0)
> 	foo

Right.  That said, our current operator space (particularly the unicode segments covered) is not super well considered.  It would be great for someone to take a more systematic pass over them to rationalize things.

-Chris