{-# LANGUAGE TemplateHaskell #-}
{-# OPTIONS_GHC -Wno-incomplete-uni-patterns #-}
{-# OPTIONS_HADDOCK hide #-}
module Data.Sum.Templates
( mkElemIndexTypeFamily
, mkApplyInstance
) where
import Language.Haskell.TH
import Unsafe.Coerce (unsafeCoerce)
mkElemIndexTypeFamily :: Integer -> Dec
mkElemIndexTypeFamily paramN =
ClosedTypeFamilyD (TypeFamilyHead elemIndex [KindedTV t functorK, KindedTV ts (AppT ListT functorK)] (KindSig (ConT nat)) Nothing) ((mkEquation <$> [0..pred paramN]) ++ errorCase)
where [elemIndex, t, ts, nat] = mkName <$> ["ElemIndex", "t", "ts", "Nat"]
functorK = AppT (AppT ArrowT StarT) StarT
mkT = VarT . mkName . ('t' :) . show
mkEquation i = TySynEqn [ mkT i, typeListT WildCardT (mkT <$> [0..i]) ] (LitT (NumTyLit i))
typeErrN = mkName "TypeError"
textN = mkName "Text"
next = mkName ":<>:"
above = mkName ":$$:"
shw = mkName "ShowType"
errorCase = [ TySynEqn
[ VarT t , VarT ts ]
(AppT
(ConT typeErrN)
(AppT
(AppT (PromotedT above)
(AppT (AppT (PromotedT next)
(AppT (AppT
(PromotedT next)
(AppT (PromotedT textN) (LitT (StrTyLit "'"))))
(AppT (PromotedT shw) (VarT t))))
(AppT (PromotedT textN) (LitT (StrTyLit "' is not a member of the type-level list")))))
(AppT (PromotedT shw) (VarT ts))))
]
mkApplyInstance :: Integer -> Dec
mkApplyInstance paramN =
InstanceD Nothing (AppT constraint <$> typeParams) (AppT (AppT (ConT applyC) constraint) (typeListT PromotedNilT typeParams))
[ FunD apply (zipWith mkClause [0..] typeParams)
, PragmaD (InlineP apply Inlinable FunLike AllPhases)
]
where typeParams = VarT . mkName . ('f' :) . show <$> [0..pred paramN]
[applyC, apply, f, r, union] = mkName <$> ["Apply", "apply", "f", "r", "Sum"]
[constraint, a] = VarT . mkName <$> ["constraint", "a"]
mkClause i nthType = Clause
[ VarP f, ConP union [ LitP (IntegerL i), VarP r ] ]
(NormalB (AppE (VarE f) (SigE (AppE (VarE 'unsafeCoerce) (VarE r)) (AppT nthType a))))
[]
typeListT :: Type -> [Type] -> Type
typeListT = foldr (AppT . AppT PromotedConsT)