Is it possible to make early exit in do-try-catch block? (Like `guard`)

[anandabits (Matthew Johnson)]

@kelin

prevent mixing problems this feature could be implemented as a similar, but separate construction.

What "mixing problems"? I don't think there are "mixing problems" as long as we don't allow else to catch errors. If we're going to add this feature I think we should do it in a way that integrates nicely with the existing feature, allowing unwrapping, pattern matching, boolean expressions and error handling to be freely intermixed in guard statements.