What is scala's experimental virtual pattern matcher?

Question

I\'ve seen quite a few mentions recently of the new \"virtualized\" pattern matcher for scala. I missed the memo explaining what it actually was...

Answer 1

The "virtualized" pattern matcher is a rewrite of the existing matcher. The motivation for doing this was to support virtualization of pattern matching for the polymorphic embedded DSLs, not relevant for 2.10.

As Iulian says in the comments below: It's very similar to how for-comprehensions are compiled: instead of directly generating code, they are translated to foreach, map, filter etc. Pattern matching could then be translated to a series of method calls, that DSLs could overwrite. The default implementation will respect the current semantics, and the challenge is to make it as efficient as the current one. It seems Adriaan is very close to this goal. The 'virtualized' implementation is simpler, and fixes several bugs in the current implementation.

The "polymorphic embedded DSLs" are the idea that one might write programs in scala that are not supposed to be run on the JVM. That is, scalac will produce an output which describes what the program is doing. This may then be re-compiled against a specific architecture. Such things have been talked about at ScalaDays 2011.

This rewrite will eventually become the standard scala pattern matcher. The old pattern matcher was (as I understand it) unmaintainable.