module Data.Derive.Traversable(makeTraversable, makeTraversableN) where
import Language.Haskell.TH.All
import Data.DeriveTraversal
makeTraversable :: Derivation
makeTraversable = makeTraversableN 1
makeTraversableN :: Int -> Derivation
makeTraversableN n = traversalDerivation1 traverseTraversal{traversalArg = n} "Traversable"
traverseTraversal = defaultTraversalType
{ traversalName = "traverse"
, traversalId = l0 "pure"
, traversalPlus = fail "variable used in multiple positions in a data type"
, traverseTuple = \args -> liftAN (ConE $ tupleDataName $ length args) args
, traverseCtor = \ctor -> liftAN (l0 ctor)
, traverseFunc = \pat rhs -> sclause [vr "f", pat] rhs
}
liftAN :: Exp -> [Exp] -> Exp
liftAN base args = foldl (l2 "<*>") (l1 "pure" base) args