Documentation fix

Accidentally copied the wrong docs in.

src/Data/Generic/HKD.hs

@@ -67,41 +67,29 @@ field
 field
   = G.field' @field
 
--- | When we work with records, all the fields are named, and we can refer to
--- them using these names. This class provides a lens from our HKD structure to
--- any @f@-wrapped field.
+-- | Product types /without/ named fields can't be addressed by field name (for
+-- very obvious reason), so we instead need to address them with their
+-- "position" index. This is a one-indexed type-applied natural:
 --
--- >>> :set -XDataKinds -XDeriveGeneric
--- >>> import Control.Lens ((&), (.~))
--- >>> import Data.Monoid (Last)
--- >>> import GHC.Generics
+-- >>> import Control.Lens ((^.))
 --
--- >>> data User = User { name :: String, age :: Int } deriving (Generic, Show)
--- >>> type Partial a = HKD a Last
+-- >>> :t mempty @(HKD (Int, String) []) ^. position @1
+-- mempty @(HKD (Int, String) []) ^. position @1 :: [Int]
 --
--- We can create an empty partial @User@ and set its name to \"Tom\" (which, in
--- this case, is @pure \"Tom\" :: Last String@):
+-- As we're using the wonderful @generic-lens@ library under the hood, we also
+-- get some beautiful error messages when things go awry:
 --
--- >>> mempty @(Partial User) & field @"name" .~ pure "Tom"
--- User {name = Last {getLast = Just "Tom"}, age = Last {getLast = Nothing}}
---
--- Thanks to some @generic-lens@ magic, we also get some pretty magical type
--- errors! If we create a (complete) partial user:
---
--- >>> import Data.Generic.HKD.Construction (deconstruct)
--- >>> total = deconstruct @Last (User "Tom" 25)
---
--- ... and then try to access a field that isn't there, we get a friendly
--- message to point us in the right direction:
---
--- >>> total & field @"oops" .~ pure ()
+-- >>> import Data.Generic.HKD.Construction
+-- >>> deconstruct ("Hello", True) ^. position @4
 -- ...
 -- ... error:
--- ... • The type HKD User Last does not contain a field named 'oops'.
+-- ... • The type HKD
+-- ...              ([Char], Bool) f does not contain a field at position 4
 -- ...
 position
   :: forall index f structure inner
    . G.HasPosition' index (HKD structure f) (f inner)
   => G.Lens' (HKD structure f) (f inner)
+
 position
   = G.position' @index