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PLift bidirectionality #130

Merged
merged 4 commits into from
Jan 18, 2022
Merged

PLift bidirectionality #130

merged 4 commits into from
Jan 18, 2022

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L-as
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@L-as L-as commented Jan 18, 2022

L-as added 4 commits January 14, 2022 23:21
@L-as
Draft PLift bidirectionality
e986557 
This makes `pconstant True` be inferred to be of type `Term s PBool`.

There is however an issue: deriving via seems to work quite suboptimally.

We need two derives because there are two type classes now:
```haskell
data PBool (s :: S) = PTrue | PFalse
  deriving (PUnsafeLiftDecl) via (DerivePLiftViaCoercible Bool PBool Bool)

deriving via (DerivePConstant Bool) PBool instance (PConstant Bool)
```

The issue then is that the instance is:
```haskell
instance (PConstant h, PConstanted h ~ DerivePLiftViaCoercible h p r, Coercible h r, PLC.DefaultUni `PLC.Includes` r) => PUnsafeLiftDecl (DerivePLiftViaCoercible h p r) where
```
`PConstanted h ~ DerivePLiftViaCoercible h p r` fails to hold, because `PConstanted h` is set by another
derive. I'm not sure whether this is easy to fix.

The reason I switched away from functional dependencies is ironically that it seemed
easier to make newtype derives work.

Is there any solution that doesn't involve TH?
@L-as
Rework PLift, add type role to Term, and remove bogus derivations
f87b4fa
@L-as
Merge remote-tracking branch 'origin/staging' into las/1
8956c51
@L-as
Prevent unsound uses of DerivePConstantViaData
580c742
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L-as commented Jan 18, 2022

@t1lde I fixed the issues, and I catched some unsoundness thanks to you!

@L-as L-as merged commit 56e6c6b into staging Jan 18, 2022
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