diff --git a/CHANGELOG.md b/CHANGELOG.md new file mode 100644 --- /dev/null +++ b/CHANGELOG.md @@ -0,0 +1,4 @@ +# Changelog + +## v0 2020-06-20 + - First release diff --git a/Data/DeriveLiftedInstances.hs b/Data/DeriveLiftedInstances.hs new file mode 100644 --- /dev/null +++ b/Data/DeriveLiftedInstances.hs @@ -0,0 +1,118 @@ +{-# LANGUAGE ViewPatterns #-} +{-# LANGUAGE TemplateHaskell #-} +{-# OPTIONS_GHC -fno-warn-orphans #-} +----------------------------------------------------------------------------- +-- | +-- Module : Data.DeriveLiftedInstances +-- Copyright : (c) Sjoerd Visscher 2020 +-- +-- Maintainer : sjoerd@w3future.com +-- Stability : experimental +-- Portability : non-portable +----------------------------------------------------------------------------- +module Data.DeriveLiftedInstances ( + -- * Deriving instances + deriveInstance, + -- * Derivators for any class + idDeriv, newtypeDeriv, isoDeriv, + -- * Derivators for algebraic classes + -- $algebraic-classes + apDeriv, tupleDeriv, unitDeriv, + showDeriv, ShowsPrec(..), + -- * Creating derivators + Derivator(..) +) where + +import Language.Haskell.TH +import Data.DeriveLiftedInstances.Internal +import Control.Arrow ((***)) +import Control.Applicative (liftA2) + +-- $algebraic-classes +-- Algebraic classes are type classes where all the methods return a value of the same type, which is also the class parameter. +-- Examples from base are `Num` and `Monoid`. + +-- | Given how to derive an instance for @a@, `apDeriv` creates a `Derivator` for @f a@, +-- when @f@ is an instance of `Applicative`. Example: +-- +-- @ +-- `deriveInstance` (`apDeriv` `idDeriv`) [t| forall a. `Num` a => `Num` [a] |] +-- +-- > [2, 3] `*` [5, 10] +-- [10, 20, 15, 30] +-- @ +apDeriv :: Derivator -> Derivator +apDeriv deriv = deriv { + res = \v -> [| fmap (\w -> $(res deriv [| w |])) $v |], + op = \nm o -> [| pure $(op deriv nm o) |], + arg = \ty e -> [| pure $(arg deriv ty e) |], + var = \fold v -> + [| fmap (\w -> $(var deriv fold [| w |])) ($(fold [| traverse |] [| id |]) $v) |], + ap = \f a -> [| liftA2 (\g b -> $(ap deriv [| g |] [| b |])) $f $a |] +} + +-- | Given how to derive an instance for @a@ and @b@, `tupleDeriv` creates a `Derivator` for @(a, b)@. +-- +-- @ +-- `deriveInstance` (`tupleDeriv` `idDeriv` `idDeriv`) [t| forall a b. (`Num` a, `Num` b) => `Num` (a, b) |] +-- +-- > (2, 3) `*` (5, 10) +-- (10, 30) +-- @ +tupleDeriv :: Derivator -> Derivator -> Derivator +tupleDeriv l r = idDeriv { + res = \e -> [| ((\w -> $(res l [| w |])) *** (\w -> $(res r [| w |]))) $e |], + op = \nm o -> [| ($(op l nm o), $(op r nm o)) |], + arg = \ty e -> [| ($(arg l ty e), $(arg r ty e)) |], + var = \fold v -> + [| ( $(var l fold [| $(fold [| fmap |] [| fst |]) $v |]) + , $(var r fold [| $(fold [| fmap |] [| snd |]) $v |]) + ) |], + ap = \f a -> [| case ($f, $a) of ((g, h), (b, c)) -> ($(ap l [| g |] [| b |]), $(ap r [| h |] [| c |])) |] +} + +-- | A `Derivator` for @()@. +unitDeriv :: Derivator +unitDeriv = idDeriv { + op = \_ _ -> [| () |], + ap = const +} + +-- | Given how to derive an instance for @a@, and the names of a newtype wrapper around @a@, +-- `newtypeDeriv` creates a `Derivator` for that newtype. Example: +-- +-- @ +-- newtype Ap f a = Ap { getAp :: f a } deriving Show +-- `deriveInstance` (`newtypeDeriv` 'Ap 'getAp `idDeriv`) [t| forall f. `Functor` f => `Functor` (Ap f) |] +-- +-- > `fmap` (+1) (Ap [1,2,3]) +-- Ap {getAp = [2,3,4]} +-- @ +newtypeDeriv :: Name -> Name -> Derivator -> Derivator +newtypeDeriv mk un = isoDeriv (pure $ ConE mk) (pure $ VarE un) + +-- | Given how to derive an instance for @a@, and two functions of type @a `->` b@ and @b `->` a@, +-- `isoDeriv` creates a `Derivator` for @b@. (Note that the 2 functions don't have to form +-- an isomorphism, but if they don't, the new instance can break the class laws.) Example: +-- +-- @ +-- newtype X = X { unX :: `Int` } deriving `Show` +-- mkX :: `Int` -> X +-- mkX i = X (`mod` i 10) +-- `deriveInstance` (isoDeriv [| mkX |] [| unX |] `idDeriv`) [t| `Num` X |] +-- +-- > mkX 4 `^` 2 +-- X {unX = 6} +-- @ +isoDeriv :: Q Exp -> Q Exp -> Derivator -> Derivator +isoDeriv mk un deriv = deriv { + res = \v -> [| $mk $(res deriv v) |], + var = \fold v -> var deriv fold [| $(fold [| fmap |] un) $v |] +} + +deriveInstance showDeriv [t| Bounded ShowsPrec |] +deriveInstance showDeriv [t| Num ShowsPrec |] +deriveInstance showDeriv [t| Fractional ShowsPrec |] +deriveInstance showDeriv [t| Floating ShowsPrec |] +deriveInstance showDeriv [t| Semigroup ShowsPrec |] +deriveInstance showDeriv [t| Monoid ShowsPrec |] diff --git a/Data/DeriveLiftedInstances/Internal.hs b/Data/DeriveLiftedInstances/Internal.hs new file mode 100644 --- /dev/null +++ b/Data/DeriveLiftedInstances/Internal.hs @@ -0,0 +1,186 @@ +{-# LANGUAGE DeriveLift #-} +{-# LANGUAGE LambdaCase #-} +{-# LANGUAGE TupleSections #-} +{-# LANGUAGE TemplateHaskell #-} +{-# LANGUAGE RecordWildCards #-} +{-# LANGUAGE StandaloneDeriving #-} +{-# OPTIONS_GHC -fno-warn-orphans #-} +----------------------------------------------------------------------------- +-- | +-- Module : Data.DeriveLiftedInstances.Internal +-- Copyright : (c) Sjoerd Visscher 2020 +-- +-- Maintainer : sjoerd@w3future.com +-- Stability : experimental +-- Portability : non-portable +----------------------------------------------------------------------------- +module Data.DeriveLiftedInstances.Internal where + +import Language.Haskell.TH +import Language.Haskell.TH.Syntax (Lift) +import Data.Char (isAlpha) +import Data.Data (Data, gmapQl, cast) +import Data.Maybe (fromMaybe, catMaybes) +import Data.Traversable (for) + + +-- | To write your own `Derivator` you need to show how each part of a method gets lifted. +-- For example, when deriving an instance for type @a@ of the following methods: +-- +-- @ +-- meth0 :: a +-- meth1 :: Int -> a +-- meth2 :: a -> Either Bool a -> Int +-- meth3 :: Maybe [a] -> a +-- @ +-- +-- the resulting template haskell declarations are (pseudo code): +-- +-- @ +-- meth0 = $res ($op "meth0" meth0) +-- meth1 a = $res (($op "meth1" meth1) `$ap` ($arg Int a)) +-- meth2 v0 v1 = (($op "meth2" meth2) `$ap` ($var fold0 v0)) `$ap` ($var fold1 v1) +-- where +-- fold0 _ f = f +-- fold1 map f = [| $map $f |] +-- meth3 v2 = $res (($op "meth2" meth2) `$ap` ($var fold2 v2)) +-- where +-- fold2 map f = [| $map ($map $f) |] +-- @ +data Derivator = Derivator { + res :: Q Exp -> Q Exp, -- ^ Convert the result of the method + op :: Name -> Q Exp -> Q Exp, -- ^ Convert the method (still unapplied to any arguments) + arg :: Type -> Q Exp -> Q Exp, -- ^ Convert an argument + var :: (Q Exp -> Q Exp -> Q Exp) -> Q Exp -> Q Exp, -- ^ Convert a variable + ap :: Q Exp -> Q Exp -> Q Exp -- ^ Apply an argument or variable to the method +} + +varExp :: Name -> Q Exp +varExp = pure . VarE + +varPat :: Name -> Q Pat +varPat = pure . VarP + +-- | The identity `Derivator`. Not useful on its own, but often used as input for other `Derivator`s. +idDeriv :: Derivator +idDeriv = Derivator { + res = id, + op = const id, + arg = const id, + var = const id, + ap = \f a -> [| $f $a |] +} + +-- | Derive the instance with the given `Derivator` and the given instance head. +-- +-- The instance head can be passed as a template haskell type quotation, for example: +-- +-- @ +-- {-\# LANGUAGE TemplateHaskell #-} +-- [t| `Num` `ShowsPrec` |] +-- [t| forall a. `Num` a => `Num` [a] |] +-- [t| forall a b. (`Num` a, `Num` b) => `Num` (a, b) |] +-- @ +deriveInstance :: Derivator -> Q Type -> Q [Dec] +deriveInstance deriv qtyp = do + typ <- qtyp + case typ of + ForallT _ ctx (AppT (ConT className) typeName) -> + deriveInstance' deriv ctx className typeName + AppT (ConT className) typeName -> + deriveInstance' deriv [] className typeName + _ -> fail $ "No support for type: " ++ show typ + +deriveInstance' :: Derivator -> Cxt -> Name -> Type -> Q [Dec] +deriveInstance' deriv ctx className typeName = do + ClassI (ClassD _ _ [KindedTV tvn _] _ decs) _ <- reify className + impl <- for decs $ \case + SigD nm tp -> do + dec <- reify nm + case dec of + ClassOpI{} -> do + (argNames, body) <- buildOperation deriv tvn tp (op deriv nm (varExp nm)) + let args = map (\argName -> if contains argName body then VarP argName else WildP) argNames + pure $ Just $ FunD nm [Clause args (NormalB body) []] + _ -> fail $ "No support for declaration: " ++ show dec + _ -> pure Nothing + pure [InstanceD Nothing ctx (AppT (ConT className) typeName) $ catMaybes impl] + +buildOperation :: Derivator -> Name -> Type -> Q Exp -> Q ([Name], Exp) +buildOperation d nm (AppT (AppT ArrowT h) t) e | hasVar nm h = do + varNm <- newName "var" + (args, rhs) <- buildOperation d nm t (ap d e (var d (buildArgument nm h) (varExp varNm))) + pure (varNm : args, rhs) +buildOperation d nm (AppT (AppT ArrowT h) t) e = do + varNm <- newName "arg" + (args, rhs) <- buildOperation d nm t (ap d e (arg d h (varExp varNm))) + pure (varNm : args, rhs) +buildOperation d nm (ForallT _ _ t) e = buildOperation d nm t e +buildOperation d nm t e | isVar nm t = ([],) <$> res d e + | otherwise = ([],) <$> e + +buildArgument :: Name -> Type -> Q Exp -> Q Exp -> Q Exp +buildArgument nm (AppT h _) _ var | isVar nm h = var +buildArgument nm (AppT _ h) over var = [| $over $(buildArgument nm h over var) |] +buildArgument _ _ _ var = var + +isVar :: Name -> Type -> Bool +isVar nm (VarT nm') = nm == nm' +isVar nm (AppT h _) = isVar nm h +isVar _ _ = False + +hasVar :: Name -> Type -> Bool +hasVar nm (VarT nm') = nm == nm' +hasVar nm (AppT f a) = isVar nm f || hasVar nm a +hasVar _ _ = False + +tvName :: TyVarBndr -> Name +tvName (PlainTV nm) = nm +tvName (KindedTV nm _) = nm + +contains :: Data d => Name -> d -> Bool +contains nm = gmapQl (||) False (\d -> maybe (contains nm d) (== nm) $ cast d) + + +deriving instance Lift Fixity +deriving instance Lift FixityDirection + +-- | Helper for showing infix expressions +data ShowsPrec = ShowsPrec (Int -> String -> String) | ShowOp2 Fixity (Int -> String -> String) | ShowOp1 Fixity (Int -> String -> String) +instance Show ShowsPrec where + showsPrec d (ShowsPrec f) = f d + showsPrec d (ShowOp2 (Fixity p _) f) = showParen (d > p) $ f 0 + showsPrec _ (ShowOp1 _ f) = showParen True $ f 0 + +showAp :: ShowsPrec -> ShowsPrec -> ShowsPrec +showAp (ShowsPrec f) (ShowsPrec g) = ShowsPrec $ \d -> showParen (d > 10) $ f 10 . showChar ' ' . g 11 +showAp (ShowOp2 fx@(Fixity p i) f) (ShowsPrec g) = ShowOp1 fx $ \_ -> g (p + fromEnum (i /= InfixL)) . showChar ' ' . f 0 +showAp (ShowOp1 (Fixity p i) f) (ShowsPrec g) = ShowsPrec $ \d -> showParen (d > p) (f 0 . showChar ' ' . g (p + fromEnum (i /= InfixR))) +showAp _ _ = error "Unexpected use of showAp" + +-- | Derive instances for `ShowsPrec`. Example: +-- +-- @ +-- `deriveInstance` `showDeriv` [t| `Num` `ShowsPrec` |] +-- +-- > `show` ((6 `*` 7) `^` 2 :: `ShowsPrec`) +-- "fromInteger 6 * fromInteger 7 * (fromInteger 6 * fromInteger 7)" +-- @ +showDeriv :: Derivator +showDeriv = idDeriv { + op = \nm _ -> let name = nameBase nm in if isOperator name + then do + fx <- fromMaybe defaultFixity <$> reifyFixity nm + [| ShowOp2 fx $ const $ showString $(pure . LitE . StringL $ name) |] + else + [| ShowsPrec $ const $ showString $(pure . LitE . StringL $ name) |], + arg = \case + (VarT _) -> const [| ShowsPrec $ const (showString "#Unshowable#") |] + _ -> \v -> [| ShowsPrec $ flip showsPrec $v |], + var = \_ v -> [| ShowsPrec $ flip showsPrec $v |], + ap = \f a -> [| showAp $f $a |] +} + +isOperator :: String -> Bool +isOperator (c:_) = not (isAlpha c) && c /= '_' +isOperator _ = False diff --git a/LICENSE b/LICENSE new file mode 100644 --- /dev/null +++ b/LICENSE @@ -0,0 +1,201 @@ +Apache License + Version 2.0, January 2004 + http://www.apache.org/licenses/ + + TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION + + 1. 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(`mod` 10) +deriveInstance (isoDeriv [| mkX |] [| unX |] idDeriv) [t| Test X |] +deriveInstance (isoDeriv [| mkX |] [| unX |] idDeriv) [t| Eq X |] +deriveInstance (isoDeriv [| mkX |] [| unX |] idDeriv) [t| Ord X |] +deriveInstance (isoDeriv [| mkX |] [| unX |] idDeriv) [t| Num X |] + +deriveInstance showDeriv [t| Test ShowsPrec |] +deriveInstance unitDeriv [t| Test () |] +deriveInstance (apDeriv idDeriv) [t| forall a. Test a => Test [a] |] +deriveInstance (tupleDeriv idDeriv idDeriv) [t| forall a b. (Test a, Test b) => Test (a, b) |] +-- deriveInstance (newtypeDeriv 'Identity 'runIdentity idDeriv) [t| forall a. Test a => Test (Identity a) |] + +newtype Ap f a = Ap { getAp :: f a } deriving Show +deriveInstance (newtypeDeriv 'Ap 'getAp (apDeriv idDeriv)) [t| forall f a. (Applicative f, Test a) => Test (Ap f a) |] + +deriveInstance (newtypeDeriv 'Identity 'runIdentity (newtypeDeriv 'Ap 'getAp (apDeriv idDeriv))) [t| forall f a. (Applicative f, Test a) => Test (Identity (Ap f a)) |] + +newtype Id a = Id { runId :: a } +deriveInstance (apDeriv (apDeriv (newtypeDeriv 'Id 'runId idDeriv))) [t| forall a. Test a => Test (() -> Identity (Id a)) |] +deriveInstance (apDeriv (tupleDeriv idDeriv idDeriv)) [t| forall a b. (Test a, Test b) => Test (() -> (a, b)) |] +deriveInstance (tupleDeriv (apDeriv idDeriv) (newtypeDeriv 'Id 'runId idDeriv)) [t| forall a b. (Test a, Test b) => Test (() -> a, Id b) |] + +class Test1 f where + hop0 :: f a + hop0' :: f Int + hop1 :: Int -> f Int -> f Int + +instance Test1 [] where + hop0 = [] + hop0' = [1] + hop1 i = map (+ i) + +deriveInstance (newtypeDeriv 'Ap 'getAp idDeriv) [t| forall f. Test1 f => Test1 (Ap f) |] +deriveInstance (newtypeDeriv 'Ap 'getAp idDeriv) [t| forall f. Functor f => Functor (Ap f) |] +deriveInstance (newtypeDeriv 'Ap 'getAp idDeriv) [t| forall f. Applicative f => Applicative (Ap f) |] +deriveInstance (newtypeDeriv 'Ap 'getAp idDeriv) [t| forall f. Monad f => Monad (Ap f) |]