Improving pattern compilation

[johnynek]

See: https://compiler.club/compiling-pattern-matching/

Currently in Matchless we compile pattern matches into nest if/else. But a better algorithm can pretty much always compile into a switch which can be encoded in Python with a dict or directly in C or Java.

[johnynek]

One nice thing would be automatic expanding out tuple matches:

match (a, b, c):
  case (Foo(x), Bar(_), Baz(_)): ..

could be nested to avoid the allocation and deallocation of the intermediate tuple:

match a:
  case Foo(x):
    match b:
      ...

To do this, we have to make sure we expand out the product match in the correct order.