ungadtagger

Abstract GADTs from typelevel tags.

UnGADTagger encapsulates abstraction-from-GADT-tag workflow by utilizing existentials, rank2-types and kind polymorphism.

An example:

# LANGUAGE GADTs, DataKinds, KindSignatures, LambdaCase #

import Data.GADT.Untagged

data Tag = A | B

data Gadt :: Tag -> * where
  ConA :: String   -> Gadt A
  ConB :: [Gadt A] -> Gadt B
  ConC :: Integer  -> Gadt B

foo :: something -> [Untagged Gadt] -> String
foo _ = quux
  where
    quux  = concat . map baz
    baz x = match x $ \case
      ConA s  -> s
      ConB xs -> quux (map untag xs)
      ConC i  -> show i

test = foo "some cfg for e.g." (xs ++ ys)
  where
    xs = map untag [ConA "A1..", ConA "A2.."]
    ys = map untag [ConB [ConA "A3.."], ConC 456]

-- > "A1..A2..A3..456"