Hugs and GHC seem to disagree on this one:

ERROR “./DeBruijn.lhs”:111 - Cannot justify constraints in explicitly typed binding
*** Expression : (\)
*** Type : (Named a, Bind b) => Bwd a -> b -> b
*** Given context : (Named a, Bind b)
*** Constraints : Named a

Peter directed me towards:

So presumably some more type annotations are required. Can’t work out what though…

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