plan for having `_` mean placeholder function syntax, `?` mean wildcard / existential

[adriaanm]

currently, _ means existential quantification at the type level

we would like to use ? instead, and use _ for placeholder function syntax at the value and type level

(its use for anonymous higher-order type params remains)

this means we'd need a version of scala where both _ and ? are valid for denoting wildcards, but this would mean claiming the ? identifier as a reserved keyword, which would break kind-projector

at the same time, we'd add support for type lambdas ([X] => Foo[X])

[SethTisue]

Martin opened a similar ticket at scala/scala3#5379

[SethTisue]

there isn't anything to change we need to change for 2.13, I think? hence, optimistically, 2.14 milestone?

[SethTisue]

out of scope for Scala 2