#15961: TH 'Lift' instance for 'NonEmpty' -------------------------------------+------------------------------------- Reporter: fr33domlover | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: 8.6.3 Component: Template | Version: 8.6.2 Haskell | Keywords: lift, | Operating System: Unknown/Multiple instance, nonempty | Architecture: | Type of failure: Other Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- I was using `deriving Lift` on a data type and the `DeriveLift` extension: {{{#!hs import Data.List.NonEmpty import Language.Haskell.TH data T = T (NonEmpty String) Int }}} and I noticed I couldn't get an automatic instance because `NonEmpty` doesn't have a `Lift` instance. I'm wondering if an instance can be added to the `template-haskell` package (or elsewhere if that isn't the right place? I'm assuming it is because `NonEmpty` is in `base` now) Since `NonEmpty` has a `Data` instance, I suppose the following would be enough? {{{#!hs instance Data a => Lift (NonEmpty a) }}} And without using `Data` it could be: {{{#!hs nonemptyConName :: Name nonemptyConName = mkNameG DataName "base" "Data.List.NonEmpty" ":|" instance Lift a => Lift (NonEmpty a) where lift (x :| xs) = do x' <- lift x xs' <- traverse lift xs return $ ConE nonemptyConName `AppE` x' `AppE` xs' }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15961 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler