Thanks for the reply. I hope that the array and list comprehensions land soon in upstream; it's a useful and hopefully not-too-controversial feature.

I'm more ambivalent regarding the local allocations and the unboxed types. I totally understand why they'd be useful when you are trying to squeeze every last drop of performance, but they do require a not-so-trivial complexification of the language.

The local types are less invasive than the full support for typed effects. In particular, they are opt-in and associated complexity is pay-as-you-go. In my initial experiments, they seemed pretty nice to program with.