Pattern Matching as an expression
Many of our targets support pattern matching as an expression, which is a basic construct in functional programming languages.

3.10 is introducing pattern matching as a statement. This is to track progress on:

* Is python ever going to have a match expression?
* If not, should we build an alternative syntax and convince one of the ast modules to parse that syntax?

Past work: https://news.ycombinator.com/item?id=27786914