very cool! On Sat, Jan 22, 2022 at 9:33 PM David Feuer wrote:

I've put up a tiny little package[1], traverse-code, offering a generic way to "traverse" in Template Haskell's `Code m`.

class TraverseCode t where traverseCode :: Quote m => (a -> Code m b) -> t a -> Code m (t b)

I wrote this primarily as a way to "lift" operations on polymorphic data structures into Template Haskell. For example, for Data.Sequence, you can write

triple :: a -> a -> a -> Seq a triple a b c = $$(sequenceCode $ fromList [ [||a||], [||b||], [||c||] ])

The `triple` function will not form its arguments into a list and then convert it to a sequence; rather, it will build the result sequence directly, using the underlying constructors.

A generic default definition is available for all instances of Generics.Linear.Generic1. See linear-generics[2] for information about how to derive those. There's nothing particularly linear about traverse-code, but linear-generics has a more general Generic1 than GHC.Generics offers.

[1] https://hackage.haskell.org/package/traverse-code [2] https://hackage.haskell.org/package/linear-generics _______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.