2026-06-09: Informal GHC Release Status Update of a Sort

wolverian:

Somewhat incidentally, I’ve never noticed this recommendation in the GHC documentation before:

We recommend compiling any code that is intended to be run in parallel with the -feager-blackholing flag.

Huh.

I hadn’t noticed that before either, but I’m guessing it was written in the context of pure code describing a parallel computation with par/pseq, where you may well be sharing thunks between threads, and eager blackholing might plausibly save work.

My impression is that explicit concurrency (e.g. with forkIO or async) is more common these days, and IMHO is easier to think about than parallelism via par/pseq. And if you’re using explicit concurrency, you’re less likely to be sharing thunks and so the default lazy blackholing is probably better.