Re: Rank2Types

Date: 2016-05-20 04:50 am (UTC)From: [personal profile] winterkoninkje
winterkoninkje: shadowcrane (clean) (Default)
No, Hugs supported both iirc. Though I vaguely recall something about Hugs being part of the reason why GHC followed suit about calling rank-2 special. Too vague to be helpful; mpj would know more.

Because of the issues about stability under extra annotations & decent error messages, if any compiler is going so far as to deal with rank-N types I'd say it's prolly good not to actually treat rank-2 specially (since this will be unintuitive to / unhelpful for users). It's more of a technical curiosity for folks who really care about fine-grained boundaries of power/provability, and are willing to sacrifice everything else to map out the cliff's edge. This used to be a big concern in the late 20th century, though I'm not sure how popular it is anymore. In CS circles at least we've kinda thrown all that to the wind and keep looking for more and more powerful systems (MLTT, CIC, IR, ...), willing to discard all but the most crucial forms of decidability (keeping only decidability of checking type-annotations, but even that is starting to show fault lines). Most pure logicians I know are similarly focused on other issues, whether they're following the CS folks or doing their own stuff. Don't hang out with enough philosophers to know what their current foci are.
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