{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE TemplateHaskell   #-}
--------------------------------------------------------------------------------
-- |
-- Module      :  Data.Comp.Multi.Derive.Equality
-- Copyright   :  (c) 2011 Patrick Bahr
-- License     :  BSD3
-- Maintainer  :  Patrick Bahr <paba@diku.dk>
-- Stability   :  experimental
-- Portability :  non-portable (GHC Extensions)
--
-- Automatically derive instances of @EqHF@.
--
--------------------------------------------------------------------------------
module Data.Comp.Multi.Derive.Equality
    (
     EqHF(..),
     KEq(..),
     makeEqHF
    ) where

import Data.Comp.Derive.Utils
import Data.Comp.Multi.Equality
import Language.Haskell.TH hiding (Cxt, match)

{-| Derive an instance of 'EqHF' for a type constructor of any higher-order
  kind taking at least two arguments. -}
makeEqHF :: Name -> Q [Dec]
makeEqHF :: Name -> Q [Dec]
makeEqHF Name
fname = do
  Just (DataInfo Cxt
_cxt Name
name [TyVarBndr flag]
args [Con]
constrs [DerivClause]
_deriving) <- Q Info -> Q (Maybe DataInfo)
abstractNewtypeQ forall a b. (a -> b) -> a -> b
$ Name -> Q Info
reify Name
fname
  let args' :: [TyVarBndr flag]
args' = forall a. [a] -> [a]
init [TyVarBndr flag]
args
      argNames :: Cxt
argNames = forall a b. (a -> b) -> [a] -> [b]
map (Name -> Type
VarT forall b c a. (b -> c) -> (a -> b) -> a -> c
. forall {flag}. TyVarBndr flag -> Name
tyVarBndrName) (forall a. [a] -> [a]
init [TyVarBndr flag]
args')
      ftyp :: Type
ftyp = Name -> Type
VarT forall b c a. (b -> c) -> (a -> b) -> a -> c
. forall {flag}. TyVarBndr flag -> Name
tyVarBndrName forall a b. (a -> b) -> a -> b
$ forall a. [a] -> a
last [TyVarBndr flag]
args'
      complType :: Type
complType = forall (t :: * -> *) b a.
Foldable t =>
(b -> a -> b) -> b -> t a -> b
foldl Type -> Type -> Type
AppT (Name -> Type
ConT Name
name) Cxt
argNames
      preCond :: Cxt
preCond = forall a b. (a -> b) -> [a] -> [b]
map (Name -> Cxt -> Type
mkClassP ''Eq forall b c a. (b -> c) -> (a -> b) -> a -> c
. (forall a. a -> [a] -> [a]
: [])) Cxt
argNames
      classType :: Type
classType = Type -> Type -> Type
AppT (Name -> Type
ConT ''EqHF) Type
complType
  [(Name, Cxt, Maybe Type)]
constrs' <- forall (t :: * -> *) (m :: * -> *) a b.
(Traversable t, Monad m) =>
(a -> m b) -> t a -> m (t b)
mapM Con -> Q (Name, Cxt, Maybe Type)
normalConExp [Con]
constrs
  Dec
eqFDecl <- forall (m :: * -> *). Quote m => Name -> [m Clause] -> m Dec
funD 'eqHF  (forall {t :: * -> *} {a}.
Foldable t =>
Type -> t a -> [(Name, Cxt, Maybe Type)] -> [Q Clause]
eqFClauses Type
ftyp [Con]
constrs [(Name, Cxt, Maybe Type)]
constrs')
  forall (m :: * -> *) a. Monad m => a -> m a
return [Cxt -> Type -> [Dec] -> Dec
mkInstanceD Cxt
preCond Type
classType [Dec
eqFDecl]]
      where eqFClauses :: Type -> t a -> [(Name, Cxt, Maybe Type)] -> [Q Clause]
eqFClauses Type
ftyp t a
constrs [(Name, Cxt, Maybe Type)]
constrs' = forall a b. (a -> b) -> [a] -> [b]
map (Type -> (Name, Cxt, Maybe Type) -> Q Clause
genEqClause Type
ftyp) [(Name, Cxt, Maybe Type)]
constrs'
                                   forall a. [a] -> [a] -> [a]
++ forall {t :: * -> *} {m :: * -> *} {a}.
(Foldable t, Quote m) =>
t a -> [m Clause]
defEqClause t a
constrs
            defEqClause :: t a -> [m Clause]
defEqClause t a
constrs
                | forall (t :: * -> *) a. Foldable t => t a -> Int
length t a
constrs  forall a. Ord a => a -> a -> Bool
< Int
2 = []
                | Bool
otherwise = [forall (m :: * -> *).
Quote m =>
[m Pat] -> m Body -> [m Dec] -> m Clause
clause [forall (m :: * -> *). Quote m => m Pat
wildP,forall (m :: * -> *). Quote m => m Pat
wildP] (forall (m :: * -> *). Quote m => m Exp -> m Body
normalB [|False|]) []]
            genEqClause :: Type -> (Name, Cxt, Maybe Type) -> Q Clause
genEqClause Type
ftyp (Name
constr, Cxt
argts, Maybe Type
gadtTy) = do
              let n :: Int
n = forall (t :: * -> *) a. Foldable t => t a -> Int
length Cxt
argts
              [Name]
varNs <- Int -> String -> Q [Name]
newNames Int
n String
"x"
              [Name]
varNs' <- Int -> String -> Q [Name]
newNames Int
n String
"y"
              let pat :: Pat
pat = Name -> Cxt -> [Pat] -> Pat
ConP Name
constr [] forall a b. (a -> b) -> a -> b
$ forall a b. (a -> b) -> [a] -> [b]
map Name -> Pat
VarP [Name]
varNs
                  pat' :: Pat
pat' = Name -> Cxt -> [Pat] -> Pat
ConP Name
constr [] forall a b. (a -> b) -> a -> b
$ forall a b. (a -> b) -> [a] -> [b]
map Name -> Pat
VarP [Name]
varNs'
                  vars :: [Exp]
vars = forall a b. (a -> b) -> [a] -> [b]
map Name -> Exp
VarE [Name]
varNs
                  vars' :: [Exp]
vars' = forall a b. (a -> b) -> [a] -> [b]
map Name -> Exp
VarE [Name]
varNs'
                  mkEq :: Type -> Exp -> Exp -> m Exp
mkEq Type
ty Exp
x Exp
y = let (m Exp
x',m Exp
y') = (forall (m :: * -> *) a. Monad m => a -> m a
return Exp
x,forall (m :: * -> *) a. Monad m => a -> m a
return Exp
y)
                                in if Type -> Type -> Bool
containsType Type
ty (Type -> Maybe Type -> Type
getBinaryFArg Type
ftyp Maybe Type
gadtTy)
                                   then [| $x' `keq` $y'|]
                                   else [| $x' == $y'|]
                  eqs :: Q Exp
eqs = forall (m :: * -> *). Quote m => [m Exp] -> m Exp
listE forall a b. (a -> b) -> a -> b
$ forall a b c d. (a -> b -> c -> d) -> [a] -> [b] -> [c] -> [d]
zipWith3 forall {m :: * -> *}. Quote m => Type -> Exp -> Exp -> m Exp
mkEq Cxt
argts [Exp]
vars [Exp]
vars'
              Exp
body <- if Int
n forall a. Eq a => a -> a -> Bool
== Int
0
                      then [|True|]
                      else [|and $eqs|]
              forall (m :: * -> *) a. Monad m => a -> m a
return forall a b. (a -> b) -> a -> b
$ [Pat] -> Body -> [Dec] -> Clause
Clause [Pat
pat, Pat
pat'] (Exp -> Body
NormalB Exp
body) []