(Quasi)ABTs for syntax types #715
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@BekaValentine was right, it needs to include the argument. I have no idea what I was thinking. Co-Authored-By: Rebecca Valentine <[email protected]>
robrix
commented
Mar 19, 2024
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| instance Eq1 Python where | ||
| liftEq _ a b = case (a, b) of | ||
| (Noop', Noop') -> True | ||
| (Iff', Iff') -> True | ||
| (Bool' b1, Bool' b2) -> b1 == b2 | ||
| (String' s1, String' s2) -> s1 == s2 | ||
| (Throw', Throw') -> True | ||
| (Let' n1, Let' n2) -> n1 == n2 | ||
| ((:>>>), (:>>>)) -> True | ||
| (Import' i1, Import' i2) -> i1 == i2 | ||
| (Function' n1 as1, Function' n2 as2) -> n1 == n2 && as1 == as2 | ||
| (Call', Call') -> True | ||
| (ANil', ANil') -> True | ||
| (ACons', ACons') -> True | ||
| (Locate' s1, Locate' s2) -> s1 == s2 | ||
| _ -> False | ||
|
|
||
| instance Ord1 Python where | ||
| liftCompare _ a b = case (a, b) of | ||
| (Noop', Noop') -> EQ | ||
| (Noop', _) -> LT | ||
| (Iff', Iff') -> EQ | ||
| (Iff', _) -> LT | ||
| (Bool' b1, Bool' b2) -> compare b1 b2 | ||
| (Bool' _, _) -> LT | ||
| (String' s1, String' s2) -> compare s1 s2 | ||
| (String' _, _) -> LT | ||
| (Throw', Throw') -> EQ | ||
| (Throw', _) -> LT | ||
| (Let' n1, Let' n2) -> compare n1 n2 | ||
| (Let' _, _) -> LT | ||
| ((:>>>), (:>>>)) -> EQ | ||
| ((:>>>), _) -> LT | ||
| (Import' i1, Import' i2) -> compare i1 i2 | ||
| (Import' _, _) -> LT | ||
| (Function' n1 as1, Function' n2 as2) -> compare n1 n2 <> compare as1 as2 | ||
| (Function' _ _, _) -> LT | ||
| (Call', Call') -> EQ | ||
| (Call', _) -> LT | ||
| (ANil', ANil') -> EQ | ||
| (ANil', _) -> LT | ||
| (ACons', ACons') -> EQ | ||
| (ACons', _) -> LT | ||
| (Locate' s1, Locate' s2) -> compare s1 s2 | ||
| (Locate' _, _) -> LT |
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We can't derive these because GHC.Generics doesn't play well with GADTs (or the other way around, I suppose). This is substantially worse than what we'd get using standard Fix-based terms or even plain old data.
I'd rather do this than fuss with CI for old versions of the compiler.
🔥 that Functor constraint.
robrix
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Mar 19, 2024
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| -- | (Currently) untyped term representations. | ||
| data Term sig v | ||
| = Var v | ||
| | Term (sig (Term sig v)) |
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A free monad by any other name
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| instance (Eq (sig (Term sig v)), Eq v) => Eq (Term sig v) where | ||
| Var v1 == Var v2 = v1 == v2 | ||
| Term s1 == Term s2 = s1 == s2 | ||
| _ == _ = False |
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The instance head can be cleaned up (and avoid the use of UndecidableInstances) using QuantifiedConstraints. However:
- for
Ordyou end up needing to supply quantified constraints for bothEqandOrd, and - it was causing spurious CI failures for ghc9.2 and I really can't be bothered
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| foldTerm :: Functor sig => (v -> r) -> (sig r -> r) -> (Term sig v -> r) | ||
| foldTerm var sig = mendlerTerm var (\ k -> sig . fmap k) |
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Here be recursion schemes 🐉
BekaValentine
approved these changes
Mar 19, 2024
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Props to @BekaValentine for a discussion of the advantages of the approach for typed and untyped syntax. As yet we're only employing untyped syntax, but it's looking pretty reasonable.