Oh I misunderstood `type T Thing` to be an alias and not a haskell-style newtype. $ ghci GHCi, version 8.8.4: https://www.haskell.org/ghc/ :? for help P

Oh I misunderstood `type T Thing` to be an alias and not a haskell-style newtype. $ ghci GHCi, version 8.8.4: https://www.haskell.org/ghc/ :? for help Prelude> class HasField a where { field1 :: a -> Int } Prelude> data Foo = Foo Prelude> instance HasField Foo where { field1 f = 2 } Prelude> field1 Foo 2 Prelude> newtype Bar = Bar Foo Prelude> :t Bar Bar :: Foo -> Bar Prelude> field1 (Bar Foo) <interactive>:7:1: error: • No instance for (HasField Bar) arising from a use of ‘field1’ • In the expression: field1 (Bar Foo) In an equation for ‘it’: it = field1 (Bar Foo) Prelude> type Baz = Foo Prelude> field1 (Foo :: Baz) 2