[Haskell-cafe] [ANN]: traverse-code

[Carter Schonwald]

very cool!

On Sat, Jan 22, 2022 at 9:33 PM David Feuer <david.feuer at gmail.com> 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
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