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another bit that tripped me up for a long time was that my constraint solver is no longer just doing unification, it’s computing judgemental equality, and hence also normalization, evaluation under binders, etc. much larger scope.
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and the rules for pattern unification—when it’s ok to solve metas, and why—are super non-obvious to me, even after reading Miller’s papers (and every other thing I could find written on the topic whatsoever for the past three years) I still have only the vaguest intuition.
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there’s this super deep relationship between heterogeneous substitution, normalization by evaluation, pattern unification, &c., and much of it depends on the kind of dependently-typed language you’re designing; & the design space is vast & underdescribed.
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e.g., the assertion repeated in a few places that “e.g. Reed’s typing modulo trick won’t cut it for ‘full-spectrum dependent types’” doesn’t really tell me anything about why, or even what the hell ‘full-spectrum dependent types’ is supposed to mean, and context merely hints.
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Ohh, this is all really helpful! Might take me a while to unpack - I haven't gone as deep as you, but it rings many bells from looking at 's elaboration-zoo a while back. It's super handy to have some of these problems stated explicitly in this way though!
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glad I could help! and please feel free to dive deeper into any of this that you’d like, or anything you pick up as you go. I’m still very much novice in all of this; it’s proven one of the hardest nuts to crack that I’ve yet encountered in CS, which is saying rather a lot.
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Yeah for sure - at the moment I've been mainly cargo-culting off the elaboration-zoo, but it's sometimes hard to understand _why_ certain choices where made, and what the other options are. I also find papers on unification rather hard to break the ice on. 😬
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I always value the time others have put into this stuff, and want to learn as much as possible from those struggles, even if there's only so much that I can get my head around at a time! So your experience is super valuable to me! 🙂
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