{-# LANGUAGE CPP #-}
{-# LANGUAGE PatternGuards #-}

{-|
Module:      Data.Functor.Invariant.TH
Copyright:   (C) 2012-2017 Nicolas Frisby, (C) 2015-2017 Ryan Scott
License:     BSD-style (see the file LICENSE)
Maintainer:  Ryan Scott
Portability: Template Haskell

Functions to mechanically derive 'Data.Functor.Invariant.Invariant'
or 'Data.Functor.Invariant.Invariant2' instances,
or to splice 'Data.Functor.Invariant.invmap' or
'Data.Functor.Invariant.invmap2' into Haskell source code. You need to enable
the @TemplateHaskell@ language extension in order to use this module.
-}
module Data.Functor.Invariant.TH (
      -- * @deriveInvariant(2)@
      -- $deriveInvariant
      deriveInvariant
    , deriveInvariantOptions
      -- $deriveInvariant2
    , deriveInvariant2
    , deriveInvariant2Options
      -- * @makeInvmap(2)@
      -- $make
    , makeInvmap
    , makeInvmapOptions
    , makeInvmap2
    , makeInvmap2Options
      -- * 'Options'
    , Options(..)
    , defaultOptions
    ) where

import           Control.Monad (unless, when)

import           Data.Functor.Invariant.TH.Internal
import qualified Data.List as List
import qualified Data.Map as Map ((!), fromList, keys, lookup, member, size)
import           Data.Maybe

import           Language.Haskell.TH.Datatype as Datatype
import           Language.Haskell.TH.Datatype.TyVarBndr
import           Language.Haskell.TH.Lib
import           Language.Haskell.TH.Ppr
import           Language.Haskell.TH.Syntax

-------------------------------------------------------------------------------
-- User-facing API
-------------------------------------------------------------------------------

-- | Options that further configure how the functions in
-- "Data.Functor.Invariant.TH" should behave.
newtype Options = Options
  { Options -> Bool
emptyCaseBehavior :: Bool
    -- ^ If 'True', derived instances for empty data types (i.e., ones with
    --   no data constructors) will use the @EmptyCase@ language extension.
    --   If 'False', derived instances will simply use 'seq' instead.
    --   (This has no effect on GHCs before 7.8, since @EmptyCase@ is only
    --   available in 7.8 or later.)
  } deriving (Options -> Options -> Bool
forall a. (a -> a -> Bool) -> (a -> a -> Bool) -> Eq a
/= :: Options -> Options -> Bool
$c/= :: Options -> Options -> Bool
== :: Options -> Options -> Bool
$c== :: Options -> Options -> Bool
Eq, Eq Options
Options -> Options -> Bool
Options -> Options -> Ordering
Options -> Options -> Options
forall a.
Eq a
-> (a -> a -> Ordering)
-> (a -> a -> Bool)
-> (a -> a -> Bool)
-> (a -> a -> Bool)
-> (a -> a -> Bool)
-> (a -> a -> a)
-> (a -> a -> a)
-> Ord a
min :: Options -> Options -> Options
$cmin :: Options -> Options -> Options
max :: Options -> Options -> Options
$cmax :: Options -> Options -> Options
>= :: Options -> Options -> Bool
$c>= :: Options -> Options -> Bool
> :: Options -> Options -> Bool
$c> :: Options -> Options -> Bool
<= :: Options -> Options -> Bool
$c<= :: Options -> Options -> Bool
< :: Options -> Options -> Bool
$c< :: Options -> Options -> Bool
compare :: Options -> Options -> Ordering
$ccompare :: Options -> Options -> Ordering
Ord, ReadPrec [Options]
ReadPrec Options
Int -> ReadS Options
ReadS [Options]
forall a.
(Int -> ReadS a)
-> ReadS [a] -> ReadPrec a -> ReadPrec [a] -> Read a
readListPrec :: ReadPrec [Options]
$creadListPrec :: ReadPrec [Options]
readPrec :: ReadPrec Options
$creadPrec :: ReadPrec Options
readList :: ReadS [Options]
$creadList :: ReadS [Options]
readsPrec :: Int -> ReadS Options
$creadsPrec :: Int -> ReadS Options
Read, Int -> Options -> ShowS
[Options] -> ShowS
Options -> String
forall a.
(Int -> a -> ShowS) -> (a -> String) -> ([a] -> ShowS) -> Show a
showList :: [Options] -> ShowS
$cshowList :: [Options] -> ShowS
show :: Options -> String
$cshow :: Options -> String
showsPrec :: Int -> Options -> ShowS
$cshowsPrec :: Int -> Options -> ShowS
Show)

-- | Conservative 'Options' that doesn't attempt to use @EmptyCase@ (to
-- prevent users from having to enable that extension at use sites.)
defaultOptions :: Options
defaultOptions :: Options
defaultOptions = Options { emptyCaseBehavior :: Bool
emptyCaseBehavior = Bool
False }

{- $deriveInvariant

'deriveInvariant' automatically generates an 'Data.Functor.Invariant.Invariant'
instance declaration for a data type, newtype, or data family instance that has
at least one type variable.  This emulates what would (hypothetically) happen
if you could attach a @deriving 'Data.Functor.Invariant.Invariant'@ clause to
the end of a data declaration. Examples:

@
&#123;-&#35; LANGUAGE TemplateHaskell &#35;-&#125;
import Data.Functor.Invariant.TH

data Pair a = Pair a a
$('deriveInvariant' ''Pair) -- instance Invariant Pair where ...

newtype Alt f a = Alt (f a)
$('deriveInvariant' ''Alt) -- instance Invariant f => Invariant (Alt f) where ...
@

If you are using @template-haskell-2.7.0.0@ or later (i.e., GHC 7.4 or later),
'deriveInvariant' can also be used to derive 'Data.Functor.Invariant.Invariant' instances for data family
instances (which requires the @-XTypeFamilies@ extension). To do so, pass the name of
a data or newtype instance constructor to 'deriveInvariant'.  Note that the generated
code may require the @-XFlexibleInstances@ extension. Some examples:

@
&#123;-&#35; LANGUAGE FlexibleInstances, TemplateHaskell, TypeFamilies &#35;-&#125;
import Data.Functor.Invariant.TH

class AssocClass a b where
    data AssocData a b
instance AssocClass Int b where
    data AssocData Int b = AssocDataInt1 Int | AssocDataInt2 b Int
$('deriveInvariant' 'AssocDataInt1) -- instance Invariant (AssocData Int) where ...
-- Alternatively, one could use $(deriveInvariant 'AssocDataInt2)

data family DataFam a b
newtype instance DataFam () b = DataFamB b
$('deriveInvariant' 'DataFamB) -- instance Invariant (DataFam ())
@

Note that there are some limitations:

* The 'Name' argument to 'deriveInvariant' must not be a type synonym.

* With 'deriveInvariant', the argument's last type variable must be of kind @*@.
  For other ones, type variables of kind @* -> *@ are assumed to require an
  'Data.Functor.Invariant.Invariant' context. For more complicated scenarios,
  use 'makeInvmap'.

* If using the @-XDatatypeContexts@, @-XExistentialQuantification@, or @-XGADTs@
  extensions, a constraint cannot mention the last type variable. For example,
  @data Illegal a where I :: Ord a => a -> Illegal a@ cannot have a derived
  'Data.Functor.Invariant.Invariant' instance.

* If the last type variable is used within a data field of a constructor, it must only
  be used in the last argument of the data type constructor. For example, @data Legal a
  = Legal (Either Int a)@ can have a derived 'Data.Functor.Invariant.Invariant' instance,
  but @data Illegal a = Illegal (Either a a)@ cannot.

* Data family instances must be able to eta-reduce the last type variable. In other
  words, if you have a instance of the form:

  @
  data family Family a1 ... an t
  data instance Family e1 ... e2 v = ...
  @

  Then the following conditions must hold:

  1. @v@ must be a type variable.
  2. @v@ must not be mentioned in any of @e1@, ..., @e2@.

-}

-- | Generates an 'Data.Functor.Invariant.Invariant' instance declaration for the given
-- data type or data family instance.
deriveInvariant :: Name -> Q [Dec]
deriveInvariant :: Name -> Q [Dec]
deriveInvariant = Options -> Name -> Q [Dec]
deriveInvariantOptions Options
defaultOptions

-- | Like 'deriveInvariant', but takes an 'Options' argument.
deriveInvariantOptions :: Options -> Name -> Q [Dec]
deriveInvariantOptions :: Options -> Name -> Q [Dec]
deriveInvariantOptions = InvariantClass -> Options -> Name -> Q [Dec]
deriveInvariantClass InvariantClass
Invariant

{- $deriveInvariant2

'deriveInvariant2' automatically generates an
'Data.Functor.Invariant.Invariant2' instance declaration for a data type,
newtype, or data family instance that has at least two type variables.  This
emulates what would (hypothetically) happen if you could attach a @deriving
'Data.Functor.Invariant.Invariant2'@ clause to the end of a data declaration.
Examples:

@
&#123;-&#35; LANGUAGE TemplateHaskell &#35;-&#125;
import Data.Functor.Invariant.TH

data OneOrNone a b = OneL a | OneR b | None
$('deriveInvariant2' ''OneOrNone) -- instance Invariant2 OneOrNone where ...

newtype Alt2 f a b = Alt2 (f a b)
$('deriveInvariant2' ''Alt2) -- instance Invariant2 f => Invariant2 (Alt2 f) where ...
@

The same restrictions that apply to 'deriveInvariant' also apply to 'deriveInvariant2',
with some caveats:

* With 'deriveInvariant2', the last type variables must both be of kind @*@. For other
  ones, type variables of kind @* -> *@ are assumed to require an 'Data.Functor.Invariant.Invariant'
  constraint, and type variables of kind @* -> * -> *@ are assumed to require an
  'Data.Functor.Invariant.Invariant2' constraint. For more complicated scenarios, use 'makeInvmap2'.

* If using the @-XDatatypeContexts@, @-XExistentialQuantification@, or @-XGADTs@
  extensions, a constraint cannot mention either of the last two type variables. For
  example, @data Illegal2 a b where I2 :: Ord a => a -> b -> Illegal2 a b@ cannot
  have a derived 'Data.Functor.Invariant.Invariant2' instance.

* If either of the last two type variables is used within a data field of a constructor,
  it must only be used in the last two arguments of the data type constructor. For
  example, @data Legal a b = Legal (Int, Int, a, b)@ can have a derived
  'Data.Functor.Invariant.Invariant2' instance, but
  @data Illegal a b = Illegal (a, b, a, b)@ cannot.

* Data family instances must be able to eta-reduce the last two type variables. In other
  words, if you have a instance of the form:

  @
  data family Family a1 ... an t1 t2
  data instance Family e1 ... e2 v1 v2 = ...
  @

  Then the following conditions must hold:

  1. @v1@ and @v2@ must be distinct type variables.
  2. Neither @v1@ not @v2@ must be mentioned in any of @e1@, ..., @e2@.

-}

-- | Generates an 'Data.Functor.Invariant.Invariant2' instance declaration for
-- the given data type or data family instance.
deriveInvariant2 :: Name -> Q [Dec]
deriveInvariant2 :: Name -> Q [Dec]
deriveInvariant2 = Options -> Name -> Q [Dec]
deriveInvariant2Options Options
defaultOptions

-- | Like 'deriveInvariant2', but takes an 'Options' argument.
deriveInvariant2Options :: Options -> Name -> Q [Dec]
deriveInvariant2Options :: Options -> Name -> Q [Dec]
deriveInvariant2Options = InvariantClass -> Options -> Name -> Q [Dec]
deriveInvariantClass InvariantClass
Invariant2

{- $make

There may be scenarios in which you want to @invmap@ over an arbitrary data
type or data family instance without having to make the type an instance of
'Data.Functor.Invariant.Invariant'. For these cases, this module provides
several functions (all prefixed with @make-@) that splice the appropriate
lambda expression into your source code. Example:

This is particularly useful for creating instances for sophisticated data
types. For example, 'deriveInvariant' cannot infer the correct type context for
@newtype HigherKinded f a b c = HigherKinded (f a b c)@, since @f@ is of kind
@* -> * -> * -> *@. However, it is still possible to create an
'Data.Functor.Invariant.Invariant' instance for @HigherKinded@ without too much
trouble using 'makeInvmap':

@
&#123;-&#35; LANGUAGE FlexibleContexts, TemplateHaskell &#35;-&#125;
import Data.Functor.Invariant
import Data.Functor.Invariant.TH

newtype HigherKinded f a b c = HigherKinded (f a b c)

instance Invariant (f a b) => Invariant (HigherKinded f a b) where
    invmap = $(makeInvmap ''HigherKinded)
@

-}

-- | Generates a lambda expression which behaves like
-- 'Data.Functor.Invariant.invmap' (without requiring an
-- 'Data.Functor.Invariant.Invariant' instance).
makeInvmap :: Name -> Q Exp
makeInvmap :: Name -> Q Exp
makeInvmap = Options -> Name -> Q Exp
makeInvmapOptions Options
defaultOptions

-- | Like 'makeInvmap', but takes an 'Options' argument.
makeInvmapOptions :: Options -> Name -> Q Exp
makeInvmapOptions :: Options -> Name -> Q Exp
makeInvmapOptions = InvariantClass -> Options -> Name -> Q Exp
makeInvmapClass InvariantClass
Invariant

-- | Generates a lambda expression which behaves like
-- 'Data.Functor.Invariant.invmap2' (without requiring an
-- 'Data.Functor.Invariant.Invariant2' instance).
makeInvmap2 :: Name -> Q Exp
makeInvmap2 :: Name -> Q Exp
makeInvmap2 = Options -> Name -> Q Exp
makeInvmap2Options Options
defaultOptions

-- | Like 'makeInvmap2', but takes an 'Options' argument.
makeInvmap2Options :: Options -> Name -> Q Exp
makeInvmap2Options :: Options -> Name -> Q Exp
makeInvmap2Options = InvariantClass -> Options -> Name -> Q Exp
makeInvmapClass InvariantClass
Invariant2

-------------------------------------------------------------------------------
-- Code generation
-------------------------------------------------------------------------------

-- | Derive an Invariant(2) instance declaration (depending on the InvariantClass
-- argument's value).
deriveInvariantClass :: InvariantClass -> Options -> Name -> Q [Dec]
deriveInvariantClass :: InvariantClass -> Options -> Name -> Q [Dec]
deriveInvariantClass InvariantClass
iClass Options
opts Name
name = do
  DatatypeInfo
info <- Name -> Q DatatypeInfo
reifyDatatype Name
name
  case DatatypeInfo
info of
    DatatypeInfo { datatypeContext :: DatatypeInfo -> [Type]
datatypeContext   = [Type]
ctxt
                 , datatypeName :: DatatypeInfo -> Name
datatypeName      = Name
parentName
                 , datatypeInstTypes :: DatatypeInfo -> [Type]
datatypeInstTypes = [Type]
instTys
                 , datatypeVariant :: DatatypeInfo -> DatatypeVariant
datatypeVariant   = DatatypeVariant
variant
                 , datatypeCons :: DatatypeInfo -> [ConstructorInfo]
datatypeCons      = [ConstructorInfo]
cons
                 } -> do
      ([Type]
instanceCxt, Type
instanceType)
        <- InvariantClass
-> Name -> [Type] -> [Type] -> DatatypeVariant -> Q ([Type], Type)
buildTypeInstance InvariantClass
iClass Name
parentName [Type]
ctxt [Type]
instTys DatatypeVariant
variant
      (forall a. a -> [a] -> [a]
:[]) forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
`fmap` forall (m :: * -> *).
Quote m =>
m [Type] -> m Type -> [m Dec] -> m Dec
instanceD (forall (m :: * -> *) a. Monad m => a -> m a
return [Type]
instanceCxt)
                             (forall (m :: * -> *) a. Monad m => a -> m a
return Type
instanceType)
                             (InvariantClass
-> Options -> Name -> [Type] -> [ConstructorInfo] -> [Q Dec]
invmapDecs InvariantClass
iClass Options
opts Name
parentName [Type]
instTys [ConstructorInfo]
cons)

-- | Generates a declaration defining the primary function corresponding to a
-- particular class (invmap for Invariant and invmap2 for Invariant2).
invmapDecs :: InvariantClass -> Options -> Name -> [Type] -> [ConstructorInfo]
           -> [Q Dec]
invmapDecs :: InvariantClass
-> Options -> Name -> [Type] -> [ConstructorInfo] -> [Q Dec]
invmapDecs InvariantClass
iClass Options
opts Name
parentName [Type]
instTys [ConstructorInfo]
cons =
    [ forall (m :: * -> *). Quote m => Name -> [m Clause] -> m Dec
funD (InvariantClass -> Name
invmapName InvariantClass
iClass)
           [ forall (m :: * -> *).
Quote m =>
[m Pat] -> m Body -> [m Dec] -> m Clause
clause []
                    (forall (m :: * -> *). Quote m => m Exp -> m Body
normalB forall a b. (a -> b) -> a -> b
$ InvariantClass
-> Options -> Name -> [Type] -> [ConstructorInfo] -> Q Exp
makeInvmapForCons InvariantClass
iClass Options
opts Name
parentName [Type]
instTys [ConstructorInfo]
cons)
                    []
           ]
    ]

-- | Generates a lambda expression which behaves like invmap (for Invariant),
-- or invmap2 (for Invariant2).
makeInvmapClass :: InvariantClass -> Options -> Name -> Q Exp
makeInvmapClass :: InvariantClass -> Options -> Name -> Q Exp
makeInvmapClass InvariantClass
iClass Options
opts Name
name = do
  DatatypeInfo
info <- Name -> Q DatatypeInfo
reifyDatatype Name
name
  case DatatypeInfo
info of
    DatatypeInfo { datatypeContext :: DatatypeInfo -> [Type]
datatypeContext   = [Type]
ctxt
                 , datatypeName :: DatatypeInfo -> Name
datatypeName      = Name
parentName
                 , datatypeInstTypes :: DatatypeInfo -> [Type]
datatypeInstTypes = [Type]
instTys
                 , datatypeVariant :: DatatypeInfo -> DatatypeVariant
datatypeVariant   = DatatypeVariant
variant
                 , datatypeCons :: DatatypeInfo -> [ConstructorInfo]
datatypeCons      = [ConstructorInfo]
cons
                 } ->
      -- We force buildTypeInstance here since it performs some checks for whether
      -- or not the provided datatype can actually have invmap/invmap2
      -- implemented for it, and produces errors if it can't.
      InvariantClass
-> Name -> [Type] -> [Type] -> DatatypeVariant -> Q ([Type], Type)
buildTypeInstance InvariantClass
iClass Name
parentName [Type]
ctxt [Type]
instTys DatatypeVariant
variant
        forall (m :: * -> *) a b. Monad m => m a -> m b -> m b
>> InvariantClass
-> Options -> Name -> [Type] -> [ConstructorInfo] -> Q Exp
makeInvmapForCons InvariantClass
iClass Options
opts Name
parentName [Type]
instTys [ConstructorInfo]
cons

-- | Generates a lambda expression for invmap(2) for the given constructors.
-- All constructors must be from the same type.
makeInvmapForCons :: InvariantClass -> Options -> Name -> [Type] -> [ConstructorInfo]
                  -> Q Exp
makeInvmapForCons :: InvariantClass
-> Options -> Name -> [Type] -> [ConstructorInfo] -> Q Exp
makeInvmapForCons InvariantClass
iClass Options
opts Name
_parentName [Type]
instTys [ConstructorInfo]
cons = do
    Name
value      <- forall (m :: * -> *). Quote m => String -> m Name
newName String
"value"
    [Name]
covMaps    <- String -> Int -> Q [Name]
newNameList String
"covMap" Int
numNbs
    [Name]
contraMaps <- String -> Int -> Q [Name]
newNameList String
"contraMap" Int
numNbs

    let mapFuns :: [(Name, Name)]
mapFuns    = forall a b. [a] -> [b] -> [(a, b)]
zip [Name]
covMaps [Name]
contraMaps
        lastTyVars :: [Name]
lastTyVars = forall a b. (a -> b) -> [a] -> [b]
map Type -> Name
varTToName forall a b. (a -> b) -> a -> b
$ forall a. Int -> [a] -> [a]
drop (forall (t :: * -> *) a. Foldable t => t a -> Int
length [Type]
instTys forall a. Num a => a -> a -> a
- Int
numNbs) [Type]
instTys
        tvMap :: Map Name (Name, Name)
tvMap      = forall k a. Ord k => [(k, a)] -> Map k a
Map.fromList forall a b. (a -> b) -> a -> b
$ forall a b. [a] -> [b] -> [(a, b)]
zip [Name]
lastTyVars [(Name, Name)]
mapFuns
        argNames :: [Name]
argNames   = forall (t :: * -> *) a. Foldable t => t [a] -> [a]
concat (forall a. [[a]] -> [[a]]
List.transpose [[Name]
covMaps, [Name]
contraMaps]) forall a. [a] -> [a] -> [a]
++ [Name
value]
    forall (m :: * -> *). Quote m => [m Pat] -> m Exp -> m Exp
lamE (forall a b. (a -> b) -> [a] -> [b]
map forall (m :: * -> *). Quote m => Name -> m Pat
varP [Name]
argNames)
        forall b c a. (b -> c) -> (a -> b) -> a -> c
. forall (m :: * -> *). Quote m => [m Exp] -> m Exp
appsE
        forall a b. (a -> b) -> a -> b
$ [ forall (m :: * -> *). Quote m => Name -> m Exp
varE forall a b. (a -> b) -> a -> b
$ InvariantClass -> Name
invmapConstName InvariantClass
iClass
          , Name -> Map Name (Name, Name) -> Q Exp
makeFun Name
value Map Name (Name, Name)
tvMap
          ] forall a. [a] -> [a] -> [a]
++ forall a b. (a -> b) -> [a] -> [b]
map forall (m :: * -> *). Quote m => Name -> m Exp
varE [Name]
argNames
  where
    numNbs :: Int
    numNbs :: Int
numNbs = forall a. Enum a => a -> Int
fromEnum InvariantClass
iClass

    makeFun :: Name -> TyVarMap -> Q Exp
    makeFun :: Name -> Map Name (Name, Name) -> Q Exp
makeFun Name
value Map Name (Name, Name)
tvMap = do
#if MIN_VERSION_template_haskell(2,9,0)
      [Role]
roles <- Name -> Q [Role]
reifyRoles Name
_parentName
      let rroles :: [Role]
rroles = [Role]
roles
#endif
      case () of
        ()
_

#if MIN_VERSION_template_haskell(2,9,0)
          | (forall (t :: * -> *) a. Foldable t => t a -> Int
length [Role]
rroles forall a. Ord a => a -> a -> Bool
>= Int
numNbs) Bool -> Bool -> Bool
&&
            (forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
all (forall a. Eq a => a -> a -> Bool
== Role
PhantomR) (forall a. Int -> [a] -> [a]
drop (forall (t :: * -> *) a. Foldable t => t a -> Int
length [Role]
rroles forall a. Num a => a -> a -> a
- Int
numNbs) [Role]
rroles))
         -> forall (m :: * -> *). Quote m => Name -> m Exp
varE Name
coerceValName forall (m :: * -> *). Quote m => m Exp -> m Exp -> m Exp
`appE` forall (m :: * -> *). Quote m => Name -> m Exp
varE Name
value
#endif

          | forall (t :: * -> *) a. Foldable t => t a -> Bool
null [ConstructorInfo]
cons Bool -> Bool -> Bool
&& Options -> Bool
emptyCaseBehavior Options
opts Bool -> Bool -> Bool
&& Bool
ghc7'8OrLater
         -> forall (m :: * -> *). Quote m => m Exp -> [m Match] -> m Exp
caseE (forall (m :: * -> *). Quote m => Name -> m Exp
varE Name
value) []

          | forall (t :: * -> *) a. Foldable t => t a -> Bool
null [ConstructorInfo]
cons
         -> forall (m :: * -> *). Quote m => m Exp -> m Exp -> m Exp
appE (forall (m :: * -> *). Quote m => Name -> m Exp
varE Name
seqValName) (forall (m :: * -> *). Quote m => Name -> m Exp
varE Name
value) forall (m :: * -> *). Quote m => m Exp -> m Exp -> m Exp
`appE`
            forall (m :: * -> *). Quote m => m Exp -> m Exp -> m Exp
appE (forall (m :: * -> *). Quote m => Name -> m Exp
varE Name
errorValName)
                 (forall (m :: * -> *). Quote m => String -> m Exp
stringE forall a b. (a -> b) -> a -> b
$ String
"Void " forall a. [a] -> [a] -> [a]
++ Name -> String
nameBase (InvariantClass -> Name
invmapName InvariantClass
iClass))

          | Bool
otherwise
         -> forall (m :: * -> *). Quote m => m Exp -> [m Match] -> m Exp
caseE (forall (m :: * -> *). Quote m => Name -> m Exp
varE Name
value)
                  (forall a b. (a -> b) -> [a] -> [b]
map (InvariantClass
-> Map Name (Name, Name) -> ConstructorInfo -> Q Match
makeInvmapForCon InvariantClass
iClass Map Name (Name, Name)
tvMap) [ConstructorInfo]
cons)

    ghc7'8OrLater :: Bool
#if __GLASGOW_HASKELL__ >= 708
    ghc7'8OrLater :: Bool
ghc7'8OrLater = Bool
True
#else
    ghc7'8OrLater = False
#endif

-- | Generates a match for invmap(2) for a single constructor.
makeInvmapForCon :: InvariantClass -> TyVarMap -> ConstructorInfo -> Q Match
makeInvmapForCon :: InvariantClass
-> Map Name (Name, Name) -> ConstructorInfo -> Q Match
makeInvmapForCon InvariantClass
iClass Map Name (Name, Name)
tvMap
  con :: ConstructorInfo
con@(ConstructorInfo { constructorName :: ConstructorInfo -> Name
constructorName    = Name
conName
                       , constructorContext :: ConstructorInfo -> [Type]
constructorContext = [Type]
ctxt }) = do
    forall (f :: * -> *). Applicative f => Bool -> f () -> f ()
when (forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
any (Type -> [Name] -> Bool
`predMentionsName` forall k a. Map k a -> [k]
Map.keys Map Name (Name, Name)
tvMap) [Type]
ctxt
            Bool -> Bool -> Bool
|| forall k a. Map k a -> Int
Map.size Map Name (Name, Name)
tvMap forall a. Ord a => a -> a -> Bool
< forall a. Enum a => a -> Int
fromEnum InvariantClass
iClass) forall a b. (a -> b) -> a -> b
$
      forall a. Name -> Q a
existentialContextError Name
conName
    [Exp -> Q Exp]
parts <- forall a.
InvariantClass
-> Map Name (Name, Name) -> FFoldType a -> ConstructorInfo -> Q [a]
foldDataConArgs InvariantClass
iClass Map Name (Name, Name)
tvMap FFoldType (Exp -> Q Exp)
ft_invmap ConstructorInfo
con
    Name -> [Exp -> Q Exp] -> Q Match
match_for_con Name
conName [Exp -> Q Exp]
parts
  where
    ft_invmap :: FFoldType (Exp -> Q Exp)
    ft_invmap :: FFoldType (Exp -> Q Exp)
ft_invmap = FT { ft_triv :: Exp -> Q Exp
ft_triv   = forall (m :: * -> *) a. Monad m => a -> m a
return
                   , ft_var :: Name -> Exp -> Q Exp
ft_var    = \Name
v Exp
x -> forall (m :: * -> *) a. Monad m => a -> m a
return forall a b. (a -> b) -> a -> b
$ Name -> Exp
VarE (forall a b. (a, b) -> a
fst (Map Name (Name, Name)
tvMap forall k a. Ord k => Map k a -> k -> a
Map.! Name
v)) Exp -> Exp -> Exp
`AppE` Exp
x
                   , ft_co_var :: Name -> Exp -> Q Exp
ft_co_var = \Name
v Exp
x -> forall (m :: * -> *) a. Monad m => a -> m a
return forall a b. (a -> b) -> a -> b
$ Name -> Exp
VarE (forall a b. (a, b) -> b
snd (Map Name (Name, Name)
tvMap forall k a. Ord k => Map k a -> k -> a
Map.! Name
v)) Exp -> Exp -> Exp
`AppE` Exp
x
                   , ft_fun :: (Exp -> Q Exp) -> (Exp -> Q Exp) -> Exp -> Q Exp
ft_fun    = \Exp -> Q Exp
g Exp -> Q Exp
h Exp
x -> (Exp -> Q Exp) -> Q Exp
mkSimpleLam forall a b. (a -> b) -> a -> b
$ \Exp
b -> do
                       Exp
gg <- Exp -> Q Exp
g Exp
b
                       Exp -> Q Exp
h forall a b. (a -> b) -> a -> b
$ Exp
x Exp -> Exp -> Exp
`AppE` Exp
gg
                   , ft_tup :: TupleSort -> [Exp -> Q Exp] -> Exp -> Q Exp
ft_tup    = forall a.
(Name -> [a] -> Q Match) -> TupleSort -> [a] -> Exp -> Q Exp
mkSimpleTupleCase Name -> [Exp -> Q Exp] -> Q Match
match_for_con
                   , ft_ty_app :: Bool -> [(Type, Exp -> Q Exp, Exp -> Q Exp)] -> Exp -> Q Exp
ft_ty_app = \Bool
contravariant [(Type, Exp -> Q Exp, Exp -> Q Exp)]
argGs Exp
x -> do
                       let inspect :: (Type, Exp -> Q Exp, Exp -> Q Exp) -> [Q Exp]
                           inspect :: (Type, Exp -> Q Exp, Exp -> Q Exp) -> [Q Exp]
inspect (Type
argTy, Exp -> Q Exp
g, Exp -> Q Exp
h)
                             -- If the argument type is a bare occurrence of one
                             -- of the data type's last type variables, then we
                             -- can generate more efficient code.
                             -- This was inspired by GHC#17880.
                             | Just Name
argVar <- Type -> Maybe Name
varTToName_maybe Type
argTy
                             , Just (Name
covMap, Name
contraMap) <- forall k a. Ord k => k -> Map k a -> Maybe a
Map.lookup Name
argVar Map Name (Name, Name)
tvMap
                             = forall a b. (a -> b) -> [a] -> [b]
map (forall (m :: * -> *) a. Monad m => a -> m a
return forall b c a. (b -> c) -> (a -> b) -> a -> c
. Name -> Exp
VarE) forall a b. (a -> b) -> a -> b
$
                               if Bool
contravariant
                                  then [Name
contraMap, Name
covMap]
                                  else [Name
covMap, Name
contraMap]
                             | Bool
otherwise
                             = [(Exp -> Q Exp) -> Q Exp
mkSimpleLam Exp -> Q Exp
g, (Exp -> Q Exp) -> Q Exp
mkSimpleLam Exp -> Q Exp
h]
                       forall (m :: * -> *). Quote m => [m Exp] -> m Exp
appsE forall a b. (a -> b) -> a -> b
$ forall (m :: * -> *). Quote m => Name -> m Exp
varE (InvariantClass -> Name
invmapName (forall a. Enum a => Int -> a
toEnum (forall (t :: * -> *) a. Foldable t => t a -> Int
length [(Type, Exp -> Q Exp, Exp -> Q Exp)]
argGs)))
                             forall a. a -> [a] -> [a]
: forall (t :: * -> *) a b. Foldable t => (a -> [b]) -> t a -> [b]
concatMap (Type, Exp -> Q Exp, Exp -> Q Exp) -> [Q Exp]
inspect [(Type, Exp -> Q Exp, Exp -> Q Exp)]
argGs
                            forall a. [a] -> [a] -> [a]
++ [forall (m :: * -> *) a. Monad m => a -> m a
return Exp
x]
                   , ft_forall :: [TyVarBndrSpec] -> (Exp -> Q Exp) -> Exp -> Q Exp
ft_forall  = \[TyVarBndrSpec]
_ Exp -> Q Exp
g Exp
x -> Exp -> Q Exp
g Exp
x
                   , ft_bad_app :: Exp -> Q Exp
ft_bad_app = \Exp
_ -> forall a. Name -> Q a
outOfPlaceTyVarError Name
conName
                   }

    -- Con a1 a2 ... -> Con (f1 a1) (f2 a2) ...
    match_for_con :: Name -> [Exp -> Q Exp] -> Q Match
    match_for_con :: Name -> [Exp -> Q Exp] -> Q Match
match_for_con = forall a. (Name -> [a] -> Q Exp) -> Name -> [Exp -> a] -> Q Match
mkSimpleConMatch forall a b. (a -> b) -> a -> b
$ \Name
conName' [Q Exp]
xs ->
       forall (m :: * -> *). Quote m => [m Exp] -> m Exp
appsE (forall (m :: * -> *). Quote m => Name -> m Exp
conE Name
conName'forall a. a -> [a] -> [a]
:[Q Exp]
xs) -- Con x1 x2 ..

-------------------------------------------------------------------------------
-- Template Haskell reifying and AST manipulation
-------------------------------------------------------------------------------

-- For the given Types, generate an instance context and head. Coming up with
-- the instance type isn't as simple as dropping the last types, as you need to
-- be wary of kinds being instantiated with *.
-- See Note [Type inference in derived instances]
buildTypeInstance :: InvariantClass
                  -- ^ Invariant or Invariant2
                  -> Name
                  -- ^ The type constructor or data family name
                  -> Cxt
                  -- ^ The datatype context
                  -> [Type]
                  -- ^ The types to instantiate the instance with
                  -> DatatypeVariant
                  -- ^ Are we dealing with a data family instance or not
                  -> Q (Cxt, Type)
buildTypeInstance :: InvariantClass
-> Name -> [Type] -> [Type] -> DatatypeVariant -> Q ([Type], Type)
buildTypeInstance InvariantClass
iClass Name
tyConName [Type]
dataCxt [Type]
varTysOrig DatatypeVariant
variant = do
    -- Make sure to expand through type/kind synonyms! Otherwise, the
    -- eta-reduction check might get tripped up over type variables in a
    -- synonym that are actually dropped.
    -- (See GHC Trac #11416 for a scenario where this actually happened.)
    [Type]
varTysExp <- forall (t :: * -> *) (m :: * -> *) a b.
(Traversable t, Monad m) =>
(a -> m b) -> t a -> m (t b)
mapM Type -> Q Type
resolveTypeSynonyms [Type]
varTysOrig

    let remainingLength :: Int
        remainingLength :: Int
remainingLength = forall (t :: * -> *) a. Foldable t => t a -> Int
length [Type]
varTysOrig forall a. Num a => a -> a -> a
- forall a. Enum a => a -> Int
fromEnum InvariantClass
iClass

        droppedTysExp :: [Type]
        droppedTysExp :: [Type]
droppedTysExp = forall a. Int -> [a] -> [a]
drop Int
remainingLength [Type]
varTysExp

        droppedStarKindStati :: [StarKindStatus]
        droppedStarKindStati :: [StarKindStatus]
droppedStarKindStati = forall a b. (a -> b) -> [a] -> [b]
map Type -> StarKindStatus
canRealizeKindStar [Type]
droppedTysExp

    -- Check there are enough types to drop and that all of them are either of
    -- kind * or kind k (for some kind variable k). If not, throw an error.
    forall (f :: * -> *). Applicative f => Bool -> f () -> f ()
when (Int
remainingLength forall a. Ord a => a -> a -> Bool
< Int
0 Bool -> Bool -> Bool
|| forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
any (forall a. Eq a => a -> a -> Bool
== StarKindStatus
NotKindStar) [StarKindStatus]
droppedStarKindStati) forall a b. (a -> b) -> a -> b
$
      forall a. InvariantClass -> Name -> Q a
derivingKindError InvariantClass
iClass Name
tyConName

    let droppedKindVarNames :: [Name]
        droppedKindVarNames :: [Name]
droppedKindVarNames = [StarKindStatus] -> [Name]
catKindVarNames [StarKindStatus]
droppedStarKindStati

        -- Substitute kind * for any dropped kind variables
        varTysExpSubst :: [Type]
        varTysExpSubst :: [Type]
varTysExpSubst = forall a b. (a -> b) -> [a] -> [b]
map ([Name] -> Type -> Type
substNamesWithKindStar [Name]
droppedKindVarNames) [Type]
varTysExp

        remainingTysExpSubst, droppedTysExpSubst :: [Type]
        ([Type]
remainingTysExpSubst, [Type]
droppedTysExpSubst) =
          forall a. Int -> [a] -> ([a], [a])
splitAt Int
remainingLength [Type]
varTysExpSubst

        -- All of the type variables mentioned in the dropped types
        -- (post-synonym expansion)
        droppedTyVarNames :: [Name]
        droppedTyVarNames :: [Name]
droppedTyVarNames = forall a. TypeSubstitution a => a -> [Name]
freeVariables [Type]
droppedTysExpSubst

    -- If any of the dropped types were polykinded, ensure that there are of kind *
    -- after substituting * for the dropped kind variables. If not, throw an error.
    forall (f :: * -> *). Applicative f => Bool -> f () -> f ()
unless (forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
all Type -> Bool
hasKindStar [Type]
droppedTysExpSubst) forall a b. (a -> b) -> a -> b
$
      forall a. InvariantClass -> Name -> Q a
derivingKindError InvariantClass
iClass Name
tyConName

    let preds    :: [Maybe Pred]
        kvNames  :: [[Name]]
        kvNames' :: [Name]
        -- Derive instance constraints (and any kind variables which are specialized
        -- to * in those constraints)
        ([Maybe Type]
preds, [[Name]]
kvNames) = forall a b. [(a, b)] -> ([a], [b])
unzip forall a b. (a -> b) -> a -> b
$ forall a b. (a -> b) -> [a] -> [b]
map (InvariantClass -> Type -> (Maybe Type, [Name])
deriveConstraint InvariantClass
iClass) [Type]
remainingTysExpSubst
        kvNames' :: [Name]
kvNames' = forall (t :: * -> *) a. Foldable t => t [a] -> [a]
concat [[Name]]
kvNames

        -- Substitute the kind variables specialized in the constraints with *
        remainingTysExpSubst' :: [Type]
        remainingTysExpSubst' :: [Type]
remainingTysExpSubst' =
          forall a b. (a -> b) -> [a] -> [b]
map ([Name] -> Type -> Type
substNamesWithKindStar [Name]
kvNames') [Type]
remainingTysExpSubst

        -- We now substitute all of the specialized-to-* kind variable names with
        -- *, but in the original types, not the synonym-expanded types. The reason
        -- we do this is a superficial one: we want the derived instance to resemble
        -- the datatype written in source code as closely as possible. For example,
        -- for the following data family instance:
        --
        --   data family Fam a
        --   newtype instance Fam String = Fam String
        --
        -- We'd want to generate the instance:
        --
        --   instance C (Fam String)
        --
        -- Not:
        --
        --   instance C (Fam [Char])
        remainingTysOrigSubst :: [Type]
        remainingTysOrigSubst :: [Type]
remainingTysOrigSubst =
          forall a b. (a -> b) -> [a] -> [b]
map ([Name] -> Type -> Type
substNamesWithKindStar (forall a. Eq a => [a] -> [a] -> [a]
List.union [Name]
droppedKindVarNames [Name]
kvNames'))
            forall a b. (a -> b) -> a -> b
$ forall a. Int -> [a] -> [a]
take Int
remainingLength [Type]
varTysOrig

    Bool
isDataFamily <-
      case DatatypeVariant
variant of
        DatatypeVariant
Datatype        -> forall (m :: * -> *) a. Monad m => a -> m a
return Bool
False
        DatatypeVariant
Newtype         -> forall (m :: * -> *) a. Monad m => a -> m a
return Bool
False
        DatatypeVariant
DataInstance    -> forall (m :: * -> *) a. Monad m => a -> m a
return Bool
True
        DatatypeVariant
NewtypeInstance -> forall (m :: * -> *) a. Monad m => a -> m a
return Bool
True
#if MIN_VERSION_th_abstraction(0,5,0)
        DatatypeVariant
Datatype.TypeData -> forall a. Name -> Q a
typeDataError Name
tyConName
#endif

    let remainingTysOrigSubst' :: [Type]
        -- See Note [Kind signatures in derived instances] for an explanation
        -- of the isDataFamily check.
        remainingTysOrigSubst' :: [Type]
remainingTysOrigSubst' =
          if Bool
isDataFamily
             then [Type]
remainingTysOrigSubst
             else forall a b. (a -> b) -> [a] -> [b]
map Type -> Type
unSigT [Type]
remainingTysOrigSubst

        instanceCxt :: Cxt
        instanceCxt :: [Type]
instanceCxt = forall a. [Maybe a] -> [a]
catMaybes [Maybe Type]
preds

        instanceType :: Type
        instanceType :: Type
instanceType = Type -> Type -> Type
AppT (Name -> Type
ConT forall a b. (a -> b) -> a -> b
$ InvariantClass -> Name
invariantClassName InvariantClass
iClass)
                     forall a b. (a -> b) -> a -> b
$ Name -> [Type] -> Type
applyTyCon Name
tyConName [Type]
remainingTysOrigSubst'

    -- If the datatype context mentions any of the dropped type variables,
    -- we can't derive an instance, so throw an error.
    forall (f :: * -> *). Applicative f => Bool -> f () -> f ()
when (forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
any (Type -> [Name] -> Bool
`predMentionsName` [Name]
droppedTyVarNames) [Type]
dataCxt) forall a b. (a -> b) -> a -> b
$
      forall a. Name -> Type -> Q a
datatypeContextError Name
tyConName Type
instanceType
    -- Also ensure the dropped types can be safely eta-reduced. Otherwise,
    -- throw an error.
    forall (f :: * -> *). Applicative f => Bool -> f () -> f ()
unless ([Type] -> [Type] -> Bool
canEtaReduce [Type]
remainingTysExpSubst' [Type]
droppedTysExpSubst) forall a b. (a -> b) -> a -> b
$
      forall a. Type -> Q a
etaReductionError Type
instanceType
    forall (m :: * -> *) a. Monad m => a -> m a
return ([Type]
instanceCxt, Type
instanceType)

-- | Attempt to derive a constraint on a Type. If successful, return
-- Just the constraint and any kind variable names constrained to *.
-- Otherwise, return Nothing and the empty list.
--
-- See Note [Type inference in derived instances] for the heuristics used to
-- come up with constraints.
deriveConstraint :: InvariantClass -> Type -> (Maybe Pred, [Name])
deriveConstraint :: InvariantClass -> Type -> (Maybe Type, [Name])
deriveConstraint InvariantClass
iClass Type
t
  | Bool -> Bool
not (Type -> Bool
isTyVar Type
t) = (forall a. Maybe a
Nothing, [])
  | Bool
otherwise = case Int -> Type -> Maybe [Name]
hasKindVarChain Int
1 Type
t of
      Just [Name]
ns | InvariantClass
iClass forall a. Ord a => a -> a -> Bool
>= InvariantClass
Invariant
              -> (forall a. a -> Maybe a
Just (Name -> Name -> Type
applyClass Name
invariantTypeName Name
tName), [Name]
ns)
      Maybe [Name]
_ -> case Int -> Type -> Maybe [Name]
hasKindVarChain Int
2 Type
t of
                Just [Name]
ns | InvariantClass
iClass forall a. Eq a => a -> a -> Bool
== InvariantClass
Invariant2
                        -> (forall a. a -> Maybe a
Just (Name -> Name -> Type
applyClass Name
invariant2TypeName Name
tName), [Name]
ns)
                Maybe [Name]
_       -> (forall a. Maybe a
Nothing, [])
  where
    tName :: Name
    tName :: Name
tName = Type -> Name
varTToName Type
t

{-
Note [Kind signatures in derived instances]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

It is possible to put explicit kind signatures into the derived instances, e.g.,

  instance C a => C (Data (f :: * -> *)) where ...

But it is preferable to avoid this if possible. If we come up with an incorrect
kind signature (which is entirely possible, since our type inferencer is pretty
unsophisticated - see Note [Type inference in derived instances]), then GHC will
flat-out reject the instance, which is quite unfortunate.

Plain old datatypes have the advantage that you can avoid using any kind signatures
at all in their instances. This is because a datatype declaration uses all type
variables, so the types that we use in a derived instance uniquely determine their
kinds. As long as we plug in the right types, the kind inferencer can do the rest
of the work. For this reason, we use unSigT to remove all kind signatures before
splicing in the instance context and head.

Data family instances are trickier, since a data family can have two instances that
are distinguished by kind alone, e.g.,

  data family Fam (a :: k)
  data instance Fam (a :: * -> *)
  data instance Fam (a :: *)

If we dropped the kind signatures for C (Fam a), then GHC will have no way of
knowing which instance we are talking about. To avoid this scenario, we always
include explicit kind signatures in data family instances. There is a chance that
the inferred kind signatures will be incorrect, but if so, we can always fall back
on the make- functions.

Note [Type inference in derived instances]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Type inference is can be tricky to get right, and we want to avoid recreating the
entirety of GHC's type inferencer in Template Haskell. For this reason, we will
probably never come up with derived instance contexts that are as accurate as
GHC's. But that doesn't mean we can't do anything! There are a couple of simple
things we can do to make instance contexts that work for 80% of use cases:

1. If one of the last type parameters is polykinded, then its kind will be
   specialized to * in the derived instance. We note what kind variable the type
   parameter had and substitute it with * in the other types as well. For example,
   imagine you had

     data Data (a :: k) (b :: k) (c :: k)

   Then you'd want to derived instance to be:

     instance C (Data (a :: *))

   Not:

     instance C (Data (a :: k))

2. We naïvely come up with instance constraints using the following criteria:

   (i)  If there's a type parameter n of kind k1 -> k2 (where k1/k2 are * or kind
        variables), then generate an Invariant n constraint, and if k1/k2 are kind
        variables, then substitute k1/k2 with * elsewhere in the types. We must
        consider the case where they are kind variables because you might have a
        scenario like this:

          newtype Compose (f :: k3 -> *) (g :: k1 -> k2 -> k3) (a :: k1) (b :: k2)
            = Compose (f (g a b))

        Which would have a derived Invariant2 instance of:

          instance (Invariant f, Invariant2 g) => Invariant2 (Compose f g) where ...

   (ii) If there's a type parameter n of kind k1 -> k2 -> k3 (where k1/k2/k3 are
        * or kind variables), then generate a Invariant2 n constraint and perform
        kind substitution as in the other case.
-}

-------------------------------------------------------------------------------
-- Error messages
-------------------------------------------------------------------------------

-- | Either the given data type doesn't have enough type variables, or one of
-- the type variables to be eta-reduced cannot realize kind *.
derivingKindError :: InvariantClass -> Name -> Q a
derivingKindError :: forall a. InvariantClass -> Name -> Q a
derivingKindError InvariantClass
iClass Name
tyConName = forall (m :: * -> *) a. MonadFail m => String -> m a
fail
    forall b c a. (b -> c) -> (a -> b) -> a -> c
. String -> ShowS
showString String
"Cannot derive well-kinded instance of form ‘"
    forall b c a. (b -> c) -> (a -> b) -> a -> c
. String -> ShowS
showString String
className
    forall b c a. (b -> c) -> (a -> b) -> a -> c
. Char -> ShowS
showChar Char
' '
    forall b c a. (b -> c) -> (a -> b) -> a -> c
. Bool -> ShowS -> ShowS
showParen Bool
True
      ( String -> ShowS
showString (Name -> String
nameBase Name
tyConName)
      forall b c a. (b -> c) -> (a -> b) -> a -> c
. String -> ShowS
showString String
" ..."
      )
    forall b c a. (b -> c) -> (a -> b) -> a -> c
. String -> ShowS
showString String
"‘\n\tClass "
    forall b c a. (b -> c) -> (a -> b) -> a -> c
. String -> ShowS
showString String
className
    forall b c a. (b -> c) -> (a -> b) -> a -> c
. String -> ShowS
showString String
" expects an argument of kind "
    forall b c a. (b -> c) -> (a -> b) -> a -> c
. String -> ShowS
showString (forall a. Ppr a => a -> String
pprint forall b c a. (b -> c) -> (a -> b) -> a -> c
. Int -> Type
createKindChain forall a b. (a -> b) -> a -> b
$ forall a. Enum a => a -> Int
fromEnum InvariantClass
iClass)
    forall a b. (a -> b) -> a -> b
$ String
""
  where
    className :: String
    className :: String
className = Name -> String
nameBase forall a b. (a -> b) -> a -> b
$ InvariantClass -> Name
invariantClassName InvariantClass
iClass

-- | The data type has a DatatypeContext which mentions one of the eta-reduced
-- type variables.
datatypeContextError :: Name -> Type -> Q a
datatypeContextError :: forall a. Name -> Type -> Q a
datatypeContextError Name
dataName Type
instanceType = forall (m :: * -> *) a. MonadFail m => String -> m a
fail
    forall b c a. (b -> c) -> (a -> b) -> a -> c
. String -> ShowS
showString String
"Can't make a derived instance of ‘"
    forall b c a. (b -> c) -> (a -> b) -> a -> c
. String -> ShowS
showString (forall a. Ppr a => a -> String
pprint Type
instanceType)
    forall b c a. (b -> c) -> (a -> b) -> a -> c
. String -> ShowS
showString String
"‘:\n\tData type ‘"
    forall b c a. (b -> c) -> (a -> b) -> a -> c
. String -> ShowS
showString (Name -> String
nameBase Name
dataName)
    forall b c a. (b -> c) -> (a -> b) -> a -> c
. String -> ShowS
showString String
"‘ must not have a class context involving the last type argument(s)"
    forall a b. (a -> b) -> a -> b
$ String
""

-- | The data type has an existential constraint which mentions one of the
-- eta-reduced type variables.
existentialContextError :: Name -> Q a
existentialContextError :: forall a. Name -> Q a
existentialContextError Name
conName = forall (m :: * -> *) a. MonadFail m => String -> m a
fail
    forall b c a. (b -> c) -> (a -> b) -> a -> c
. String -> ShowS
showString String
"Constructor ‘"
    forall b c a. (b -> c) -> (a -> b) -> a -> c
. String -> ShowS
showString (Name -> String
nameBase Name
conName)
    forall b c a. (b -> c) -> (a -> b) -> a -> c
. String -> ShowS
showString String
"‘ must be truly polymorphic in the last argument(s) of the data type"
    forall a b. (a -> b) -> a -> b
$ String
""

-- | The data type mentions one of the n eta-reduced type variables in a place other
-- than the last nth positions of a data type in a constructor's field.
outOfPlaceTyVarError :: Name -> Q a
outOfPlaceTyVarError :: forall a. Name -> Q a
outOfPlaceTyVarError Name
conName = forall (m :: * -> *) a. MonadFail m => String -> m a
fail
  forall b c a. (b -> c) -> (a -> b) -> a -> c
. String -> ShowS
showString String
"Constructor ‘"
  forall b c a. (b -> c) -> (a -> b) -> a -> c
. String -> ShowS
showString (Name -> String
nameBase Name
conName)
  forall b c a. (b -> c) -> (a -> b) -> a -> c
. String -> ShowS
showString String
"‘ must only use its last two type variable(s) within"
  forall b c a. (b -> c) -> (a -> b) -> a -> c
. String -> ShowS
showString String
" the last two argument(s) of a data type"
  forall a b. (a -> b) -> a -> b
$ String
""

-- | One of the last type variables cannot be eta-reduced (see the canEtaReduce
-- function for the criteria it would have to meet).
etaReductionError :: Type -> Q a
etaReductionError :: forall a. Type -> Q a
etaReductionError Type
instanceType = forall (m :: * -> *) a. MonadFail m => String -> m a
fail forall a b. (a -> b) -> a -> b
$
    String
"Cannot eta-reduce to an instance of form \n\tinstance (...) => "
    forall a. [a] -> [a] -> [a]
++ forall a. Ppr a => a -> String
pprint Type
instanceType

#if MIN_VERSION_th_abstraction(0,5,0)
-- | We cannot implement class methods at the term level for @type data@
-- declarations, which only exist at the type level.
typeDataError :: Name -> Q a
typeDataError :: forall a. Name -> Q a
typeDataError Name
dataName = forall (m :: * -> *) a. MonadFail m => String -> m a
fail
  forall b c a. (b -> c) -> (a -> b) -> a -> c
. String -> ShowS
showString String
"Cannot derive instance for ‘"
  forall b c a. (b -> c) -> (a -> b) -> a -> c
. String -> ShowS
showString (Name -> String
nameBase Name
dataName)
  forall b c a. (b -> c) -> (a -> b) -> a -> c
. String -> ShowS
showString String
"‘, which is a ‘type data‘ declaration"
  forall a b. (a -> b) -> a -> b
$ String
""
#endif

-------------------------------------------------------------------------------
-- Generic traversal for functor-like deriving
-------------------------------------------------------------------------------

-- Much of the code below is cargo-culted from the TcGenFunctor module in GHC.

data FFoldType a      -- Describes how to fold over a Type in a functor like way
   = FT { forall a. FFoldType a -> a
ft_triv    :: a
          -- ^ Does not contain variables
        , forall a. FFoldType a -> Name -> a
ft_var     :: Name -> a
          -- ^ A bare variable
        , forall a. FFoldType a -> Name -> a
ft_co_var  :: Name -> a
          -- ^ A bare variable, contravariantly
        , forall a. FFoldType a -> a -> a -> a
ft_fun     :: a -> a -> a
          -- ^ Function type
        , forall a. FFoldType a -> TupleSort -> [a] -> a
ft_tup     :: TupleSort -> [a] -> a
          -- ^ Tuple type. The [a] is the result of folding over the
          --   arguments of the tuple.
        , forall a. FFoldType a -> Bool -> [(Type, a, a)] -> a
ft_ty_app  :: Bool -> [(Type, a, a)] -> a
          -- ^ Type app, variables only in last argument. The [(Type, a, a)]
          --   represents the last argument types. That is, they form the
          --   argument parts of @fun_ty arg_ty_1 ... arg_ty_n@.
          --
          --   The Bool is True if the Type is in a surrounding context that is
          --   contravariant, and False if the surrounding context is covariant.
          --   The two @a@ fields in [(Type, a, a)] represent the results of
          --   folding over the Type in a covariant and contravariant manner,
          --   respectively.
        , forall a. FFoldType a -> a
ft_bad_app :: a
          -- ^ Type app, variable other than in last arguments
        , forall a. FFoldType a -> [TyVarBndrSpec] -> a -> a
ft_forall  :: [TyVarBndrSpec] -> a -> a
          -- ^ Forall type
     }

-- Note that in GHC, this function is pure. It must be monadic here since we:
--
-- (1) Expand type synonyms
-- (2) Detect type family applications
--
-- Which require reification in Template Haskell, but are pure in Core.
functorLikeTraverse :: InvariantClass -- ^ Invariant or Invariant2
                    -> TyVarMap       -- ^ Variables to look for
                    -> FFoldType a    -- ^ How to fold
                    -> Type           -- ^ Type to process
                    -> Q a
functorLikeTraverse :: forall a.
InvariantClass
-> Map Name (Name, Name) -> FFoldType a -> Type -> Q a
functorLikeTraverse InvariantClass
iClass Map Name (Name, Name)
tvMap (FT { ft_triv :: forall a. FFoldType a -> a
ft_triv = a
caseTrivial,     ft_var :: forall a. FFoldType a -> Name -> a
ft_var = Name -> a
caseVar
                                     , ft_co_var :: forall a. FFoldType a -> Name -> a
ft_co_var = Name -> a
caseCoVar,     ft_fun :: forall a. FFoldType a -> a -> a -> a
ft_fun = a -> a -> a
caseFun
                                     , ft_tup :: forall a. FFoldType a -> TupleSort -> [a] -> a
ft_tup = TupleSort -> [a] -> a
caseTuple,        ft_ty_app :: forall a. FFoldType a -> Bool -> [(Type, a, a)] -> a
ft_ty_app = Bool -> [(Type, a, a)] -> a
caseTyApp
                                     , ft_bad_app :: forall a. FFoldType a -> a
ft_bad_app = a
caseWrongArg, ft_forall :: forall a. FFoldType a -> [TyVarBndrSpec] -> a -> a
ft_forall = [TyVarBndrSpec] -> a -> a
caseForAll })
                    Type
ty
  = do Type
ty' <- Type -> Q Type
resolveTypeSynonyms Type
ty
       (a
res, Bool
_) <- Bool -> Type -> Q (a, Bool)
go Bool
False Type
ty'
       forall (m :: * -> *) a. Monad m => a -> m a
return a
res
  where
    {-
    go :: Bool        -- Covariant or contravariant context
       -> Type
       -> Q (a, Bool) -- (result of type a, does type contain var)
    -}
    go :: Bool -> Type -> Q (a, Bool)
go Bool
co t :: Type
t@AppT{}
      | (Type
ArrowT, [Type
funArg, Type
funRes]) <- Type -> (Type, [Type])
unapplyTy Type
t
      = do (a
funArgR, Bool
funArgC) <- Bool -> Type -> Q (a, Bool)
go (Bool -> Bool
not Bool
co) Type
funArg
           (a
funResR, Bool
funResC) <- Bool -> Type -> Q (a, Bool)
go      Bool
co  Type
funRes
           if Bool
funArgC Bool -> Bool -> Bool
|| Bool
funResC
              then forall (m :: * -> *) a. Monad m => a -> m a
return (a -> a -> a
caseFun a
funArgR a
funResR, Bool
True)
              else Q (a, Bool)
trivial
    go Bool
co t :: Type
t@AppT{} = do
      let (Type
f, [Type]
args) = Type -> (Type, [Type])
unapplyTy Type
t
      (a
_, Bool
fc) <- Bool -> Type -> Q (a, Bool)
go Bool
co Type
f
      ([a]
xrs,       [Bool]
xcs) <- forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
fmap forall a b. [(a, b)] -> ([a], [b])
unzip forall a b. (a -> b) -> a -> b
$ forall (t :: * -> *) (m :: * -> *) a b.
(Traversable t, Monad m) =>
(a -> m b) -> t a -> m (t b)
mapM (Bool -> Type -> Q (a, Bool)
go Bool
co) [Type]
args
      ([a]
contraXrs, [Bool]
_)   <- forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
fmap forall a b. [(a, b)] -> ([a], [b])
unzip forall a b. (a -> b) -> a -> b
$ forall (t :: * -> *) (m :: * -> *) a b.
(Traversable t, Monad m) =>
(a -> m b) -> t a -> m (t b)
mapM (Bool -> Type -> Q (a, Bool)
go (Bool -> Bool
not Bool
co)) [Type]
args
      let numLastArgs, numFirstArgs :: Int
          numLastArgs :: Int
numLastArgs  = forall a. Ord a => a -> a -> a
min (forall a. Enum a => a -> Int
fromEnum InvariantClass
iClass) (forall (t :: * -> *) a. Foldable t => t a -> Int
length [Type]
args)
          numFirstArgs :: Int
numFirstArgs = forall (t :: * -> *) a. Foldable t => t a -> Int
length [Type]
args forall a. Num a => a -> a -> a
- Int
numLastArgs

          -- tuple :: TupleSort -> Q (a, Bool)
          tuple :: TupleSort -> m (a, Bool)
tuple TupleSort
tupSort = forall (m :: * -> *) a. Monad m => a -> m a
return (TupleSort -> [a] -> a
caseTuple TupleSort
tupSort [a]
xrs, Bool
True)

          -- wrongArg :: Q (a, Bool)
          wrongArg :: Q (a, Bool)
wrongArg = forall (m :: * -> *) a. Monad m => a -> m a
return (a
caseWrongArg, Bool
True)

      case () of
        ()
_ |  Bool -> Bool
not (forall (t :: * -> *). Foldable t => t Bool -> Bool
or [Bool]
xcs)
          -> Q (a, Bool)
trivial -- Variable does not occur
          -- At this point we know that xrs, xcs is not empty,
          -- and at least one xr is True
          |  TupleT Int
len <- Type
f
          -> forall {m :: * -> *}. Monad m => TupleSort -> m (a, Bool)
tuple forall a b. (a -> b) -> a -> b
$ Int -> TupleSort
Boxed Int
len
#if MIN_VERSION_template_haskell(2,6,0)
          |  UnboxedTupleT Int
len <- Type
f
          -> forall {m :: * -> *}. Monad m => TupleSort -> m (a, Bool)
tuple forall a b. (a -> b) -> a -> b
$ Int -> TupleSort
Unboxed Int
len
#endif
          |  Bool
fc Bool -> Bool -> Bool
|| forall (t :: * -> *). Foldable t => t Bool -> Bool
or (forall a. Int -> [a] -> [a]
take Int
numFirstArgs [Bool]
xcs)
          -> Q (a, Bool)
wrongArg                    -- T (..var..)    ty_1 ... ty_n
          |  Bool
otherwise                   -- T (..no var..) ty_1 ... ty_n
          -> do Bool
itf <- [Name] -> Type -> [Type] -> Q Bool
isInTypeFamilyApp [Name]
tyVarNames Type
f [Type]
args
                if Bool
itf -- We can't decompose type families, so
                       -- error if we encounter one here.
                   then Q (a, Bool)
wrongArg
                   else forall (m :: * -> *) a. Monad m => a -> m a
return ( Bool -> [(Type, a, a)] -> a
caseTyApp Bool
co forall a b. (a -> b) -> a -> b
$ forall a. Int -> [a] -> [a]
drop Int
numFirstArgs
                                              forall a b. (a -> b) -> a -> b
$ forall a b c. [a] -> [b] -> [c] -> [(a, b, c)]
zip3 [Type]
args [a]
xrs [a]
contraXrs
                               , Bool
True )
    go Bool
co (SigT Type
t Type
k) = do
      (a
_, Bool
kc) <- Bool -> Type -> Q (a, Bool)
go_kind Bool
co Type
k
      if Bool
kc
         then forall (m :: * -> *) a. Monad m => a -> m a
return (a
caseWrongArg, Bool
True)
         else Bool -> Type -> Q (a, Bool)
go Bool
co Type
t
    go Bool
co (VarT Name
v)
      | forall k a. Ord k => k -> Map k a -> Bool
Map.member Name
v Map Name (Name, Name)
tvMap
      = forall (m :: * -> *) a. Monad m => a -> m a
return (if Bool
co then Name -> a
caseCoVar Name
v else Name -> a
caseVar Name
v, Bool
True)
      | Bool
otherwise
      = Q (a, Bool)
trivial
    go Bool
co (ForallT [TyVarBndrSpec]
tvbs [Type]
_ Type
t) = do
      (a
tr, Bool
tc) <- Bool -> Type -> Q (a, Bool)
go Bool
co Type
t
      let tvbNames :: [Name]
tvbNames = forall a b. (a -> b) -> [a] -> [b]
map forall flag. TyVarBndr_ flag -> Name
tvName [TyVarBndrSpec]
tvbs
      if Bool -> Bool
not Bool
tc Bool -> Bool -> Bool
|| forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
any (forall (t :: * -> *) a. (Foldable t, Eq a) => a -> t a -> Bool
`elem` [Name]
tvbNames) [Name]
tyVarNames
         then Q (a, Bool)
trivial
         else forall (m :: * -> *) a. Monad m => a -> m a
return ([TyVarBndrSpec] -> a -> a
caseForAll [TyVarBndrSpec]
tvbs a
tr, Bool
True)
    go Bool
_ Type
_ = Q (a, Bool)
trivial

    {-
    go_kind :: Bool
            -> Kind
            -> Q (a, Bool)
    -}
#if MIN_VERSION_template_haskell(2,9,0)
    go_kind :: Bool -> Type -> Q (a, Bool)
go_kind = Bool -> Type -> Q (a, Bool)
go
#else
    go_kind _ _ = trivial
#endif

    -- trivial :: Q (a, Bool)
    trivial :: Q (a, Bool)
trivial = forall (m :: * -> *) a. Monad m => a -> m a
return (a
caseTrivial, Bool
False)

    tyVarNames :: [Name]
    tyVarNames :: [Name]
tyVarNames = forall k a. Map k a -> [k]
Map.keys Map Name (Name, Name)
tvMap

-- Fold over the arguments of a data constructor in a Functor-like way.
foldDataConArgs :: InvariantClass -> TyVarMap -> FFoldType a -> ConstructorInfo -> Q [a]
foldDataConArgs :: forall a.
InvariantClass
-> Map Name (Name, Name) -> FFoldType a -> ConstructorInfo -> Q [a]
foldDataConArgs InvariantClass
iClass Map Name (Name, Name)
tvMap FFoldType a
ft ConstructorInfo
con = do
  [Type]
fieldTys <- forall (t :: * -> *) (m :: * -> *) a b.
(Traversable t, Monad m) =>
(a -> m b) -> t a -> m (t b)
mapM Type -> Q Type
resolveTypeSynonyms forall a b. (a -> b) -> a -> b
$ ConstructorInfo -> [Type]
constructorFields ConstructorInfo
con
  forall (t :: * -> *) (m :: * -> *) a b.
(Traversable t, Monad m) =>
(a -> m b) -> t a -> m (t b)
mapM Type -> Q a
foldArg [Type]
fieldTys
  where
    -- foldArg :: Type -> Q a
    foldArg :: Type -> Q a
foldArg = forall a.
InvariantClass
-> Map Name (Name, Name) -> FFoldType a -> Type -> Q a
functorLikeTraverse InvariantClass
iClass Map Name (Name, Name)
tvMap FFoldType a
ft

-- Make a 'LamE' using a fresh variable.
mkSimpleLam :: (Exp -> Q Exp) -> Q Exp
mkSimpleLam :: (Exp -> Q Exp) -> Q Exp
mkSimpleLam Exp -> Q Exp
lam = do
  Name
n <- forall (m :: * -> *). Quote m => String -> m Name
newName String
"n"
  Exp
body <- Exp -> Q Exp
lam (Name -> Exp
VarE Name
n)
  forall (m :: * -> *) a. Monad m => a -> m a
return forall a b. (a -> b) -> a -> b
$ [Pat] -> Exp -> Exp
LamE [Name -> Pat
VarP Name
n] Exp
body

-- "Con a1 a2 a3 -> fold [x1 a1, x2 a2, x3 a3]"
--
-- @mkSimpleConMatch fold conName insides@ produces a match clause in
-- which the LHS pattern-matches on @extraPats@, followed by a match on the
-- constructor @conName@ and its arguments. The RHS folds (with @fold@) over
-- @conName@ and its arguments, applying an expression (from @insides@) to each
-- of the respective arguments of @conName@.
mkSimpleConMatch :: (Name -> [a] -> Q Exp)
                 -> Name
                 -> [Exp -> a]
                 -> Q Match
mkSimpleConMatch :: forall a. (Name -> [a] -> Q Exp) -> Name -> [Exp -> a] -> Q Match
mkSimpleConMatch Name -> [a] -> Q Exp
fold Name
conName [Exp -> a]
insides = do
  [Name]
varsNeeded <- String -> Int -> Q [Name]
newNameList String
"_arg" forall a b. (a -> b) -> a -> b
$ forall (t :: * -> *) a. Foldable t => t a -> Int
length [Exp -> a]
insides
  let pat :: Pat
pat = Name -> [Type] -> [Pat] -> Pat
ConP Name
conName
#if MIN_VERSION_template_haskell(2,18,0)
                 []
#endif
                 (forall a b. (a -> b) -> [a] -> [b]
map Name -> Pat
VarP [Name]
varsNeeded)
  Exp
rhs <- Name -> [a] -> Q Exp
fold Name
conName (forall a b c. (a -> b -> c) -> [a] -> [b] -> [c]
zipWith (\Exp -> a
i Name
v -> Exp -> a
i forall a b. (a -> b) -> a -> b
$ Name -> Exp
VarE Name
v) [Exp -> a]
insides [Name]
varsNeeded)
  forall (m :: * -> *) a. Monad m => a -> m a
return forall a b. (a -> b) -> a -> b
$ Pat -> Body -> [Dec] -> Match
Match Pat
pat (Exp -> Body
NormalB Exp
rhs) []

-- Indicates whether a tuple is boxed or unboxed, as well as its number of
-- arguments. For instance, (a, b) corresponds to @Boxed 2@, and (# a, b, c #)
-- corresponds to @Unboxed 3@.
data TupleSort
  = Boxed   Int
#if MIN_VERSION_template_haskell(2,6,0)
  | Unboxed Int
#endif

-- "case x of (a1,a2,a3) -> fold [x1 a1, x2 a2, x3 a3]"
mkSimpleTupleCase :: (Name -> [a] -> Q Match)
                  -> TupleSort -> [a] -> Exp -> Q Exp
mkSimpleTupleCase :: forall a.
(Name -> [a] -> Q Match) -> TupleSort -> [a] -> Exp -> Q Exp
mkSimpleTupleCase Name -> [a] -> Q Match
matchForCon TupleSort
tupSort [a]
insides Exp
x = do
  let tupDataName :: Name
tupDataName = case TupleSort
tupSort of
                      Boxed   Int
len -> Int -> Name
tupleDataName Int
len
#if MIN_VERSION_template_haskell(2,6,0)
                      Unboxed Int
len -> Int -> Name
unboxedTupleDataName Int
len
#endif
  Match
m <- Name -> [a] -> Q Match
matchForCon Name
tupDataName [a]
insides
  forall (m :: * -> *) a. Monad m => a -> m a
return forall a b. (a -> b) -> a -> b
$ Exp -> [Match] -> Exp
CaseE Exp
x [Match
m]