book-monads/src/ch04/s03-stackless.md
2023-05-03 12:05:38 +00:00

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# `Stackless<'a>` isn't covariant
Current hypothesis is that this comes from `EvalTree<'a>` being invariant over `'a`
due to `FnOnce` being invariant over its output,
which in turn comes from present typesysten limitations.