Always use QuantifiedConstraints, support inductive GADTs #17
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…phic instances." This reverts commit 5c50d96.
Ericson2314
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alexfmpe
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Sep 12, 2019
Co-Authored-By: Alexandre Esteves <[email protected]>
Anywhere we get an `Extract` we do it ultimately via `argDictAll`, so the `ArgDict f` constraint must already be satified in scope.
3noch
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Sep 12, 2019
Thanks! Co-Authored-By: Elliot Cameron <[email protected]>
xplat
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Sep 12, 2019
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Is it necessary to drop support for ghc < 86? |
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There might be a way, but only with copious CPP. I like what this PR does, but it is a solution in search of a problem. I think eventually we'll want it (e.g. IV debugging constraints), but for now we can just leave open. |
ali-abrar
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It is only allowed with GHC 8.6, and doesn't work very well there I'm told. https://gitlab.haskell.org/ghc/ghc/-/issues/14860 tracks the underlying issue.
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Ericson2314
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Ericson2314
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Jun 30, 2023
| -- @argDict@ is sufficient for most tasks, but this is slightly more powerful | ||
| -- in that this discharges the quantified constraints which are useful when | ||
| -- the GADT indices are not finite. | ||
| argDictAll :: f a -> Dict (Extract f a) |
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N.B. This wants to be:
Suggested change
| argDictAll :: f a -> Dict (Extract f a) | |
| argDictAll :: f a -> Dict (forall c. ConstraintsFor f c => c a)) |
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The big question is, is the following weaker?
argDictAll :: f a -> forall c. Dict (ConstraintsFor f c => c a))
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I put a manual instance in the README, but we could do it with TH later.