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It seems like it is possible to get bitten by lack of "inferable transitivity" of Members constraints in opaque contexts: https://github.com/axellang/axel/blob/purescript-backend/src/Axel/Macros.hs#L477
Author's solution actually doesn't work - it may be possible to fix it, but I think this one is a deeper problem to solve
If we explicitly write down wanted Members constraint, problem reduces down to Members es r => Members es (e:r)
Members es r => Members es (e:r)
Author here, happy to answer any questions about this specific example