-- |

-- This module implements the desugaring pass which creates newtypes for type class dictionaries

-- and value declarations for type class instances.

--

module Language.PureScript.Sugar.TypeClasses

( desugarTypeClasses

, typeClassMemberName

, superClassDictionaryNames

) where

import Prelude

import Control.Arrow (first, second)

import Control.Monad (unless)

import Control.Monad.Error.Class (MonadError(..))

import Control.Monad.State (MonadState(..), StateT, evalStateT, modify)

import Control.Monad.Supply.Class (MonadSupply)

import Data.Graph (SCC(..), stronglyConnComp)

import Data.List (find, partition)

import Data.List.NonEmpty (nonEmpty)

import Data.Map qualified as M

import Data.Maybe (catMaybes, mapMaybe, isJust)

import Data.List.NonEmpty qualified as NEL

import Data.Set qualified as S

import Data.Text (Text)

import Data.Traversable (for)

import Language.PureScript.Constants.Prim qualified as C

import Language.PureScript.Crash (internalError)

import Language.PureScript.Environment (DataDeclType(..), NameKind(..), TypeClassData(..), dictTypeName, function, makeTypeClassData, primClasses, primCoerceClasses, primIntClasses, primRowClasses, primRowListClasses, primSymbolClasses, primTypeErrorClasses, tyRecord)

import Language.PureScript.Errors hiding (isExported, nonEmpty)

import Language.PureScript.Externs (ExternsDeclaration(..), ExternsFile(..))

import Language.PureScript.Label (Label(..))

import Language.PureScript.Names (pattern ByNullSourcePos, Ident(..), ModuleName, Name(..), ProperName, ProperNameType(..), Qualified(..), QualifiedBy(..), coerceProperName, freshIdent, qualify, runIdent)

import Language.PureScript.PSString (mkString)

import Language.PureScript.Sugar.CaseDeclarations (desugarCases)

import Language.PureScript.TypeClassDictionaries (superclassName)

import Language.PureScript.Types

type MemberMap = M.Map (ModuleName, ProperName 'ClassName) TypeClassData

type Desugar = StateT MemberMap

-- |

-- Add type synonym declarations for type class dictionary types, and value declarations for type class

-- instance dictionary expressions.

--

desugarTypeClasses

:: (MonadSupply m, MonadError MultipleErrors m)

=> [ExternsFile]

-> Module

-> m Module

desugarTypeClasses externs = flip evalStateT initialState . desugarModule

where

initialState :: MemberMap

initialState =

mconcat

[ M.mapKeys (qualify C.M_Prim) primClasses

, M.mapKeys (qualify C.M_Prim_Coerce) primCoerceClasses

, M.mapKeys (qualify C.M_Prim_Row) primRowClasses

, M.mapKeys (qualify C.M_Prim_RowList) primRowListClasses

, M.mapKeys (qualify C.M_Prim_Symbol) primSymbolClasses

, M.mapKeys (qualify C.M_Prim_Int) primIntClasses

, M.mapKeys (qualify C.M_Prim_TypeError) primTypeErrorClasses

, M.fromList (externs >>= \ExternsFile{..} -> mapMaybe (fromExternsDecl efModuleName) efDeclarations)

]

fromExternsDecl

:: ModuleName

-> ExternsDeclaration

-> Maybe ((ModuleName, ProperName 'ClassName), TypeClassData)

fromExternsDecl mn (EDClass name args members implies deps tcIsEmpty) = Just ((mn, name), typeClass) where

typeClass = makeTypeClassData args members implies deps tcIsEmpty

fromExternsDecl _ _ = Nothing

desugarModule

:: (MonadSupply m, MonadError MultipleErrors m)

=> Module

-> Desugar m Module

desugarModule (Module ss coms name decls (Just exps)) = do

let (classDecls, restDecls) = partition isTypeClassDecl decls

classVerts = fmap (\d -> (d, classDeclName d, superClassesNames d)) classDecls

(classNewExpss, classDeclss) <- unzip <$> parU (stronglyConnComp classVerts) (desugarClassDecl name exps)

(restNewExpss, restDeclss) <- unzip <$> parU restDecls (desugarDecl name exps)

return $ Module ss coms name (concat restDeclss ++ concat classDeclss) $ Just (exps ++ catMaybes restNewExpss ++ catMaybes classNewExpss)

where

desugarClassDecl :: (MonadSupply m, MonadError MultipleErrors m)

=> ModuleName

-> [DeclarationRef]

-> SCC Declaration

-> Desugar m (Maybe DeclarationRef, [Declaration])

desugarClassDecl name' exps' (AcyclicSCC d) = desugarDecl name' exps' d

desugarClassDecl _ _ (CyclicSCC ds')

| Just ds'' <- nonEmpty ds' = throwError . errorMessage' (declSourceSpan (NEL.head ds'')) $ CycleInTypeClassDeclaration (NEL.map classDeclName ds'')

| otherwise = internalError "desugarClassDecl: empty CyclicSCC"

superClassesNames :: Declaration -> [Qualified (ProperName 'ClassName)]

superClassesNames (TypeClassDeclaration _ _ _ implies _ _) = fmap constraintName implies

superClassesNames _ = []

constraintName :: SourceConstraint -> Qualified (ProperName 'ClassName)

constraintName (Constraint _ cName _ _ _) = cName

classDeclName :: Declaration -> Qualified (ProperName 'ClassName)

classDeclName (TypeClassDeclaration _ pn _ _ _ _) = Qualified (ByModuleName name) pn

classDeclName _ = internalError "Expected TypeClassDeclaration"

desugarModule _ = internalError "Exports should have been elaborated in name desugaring"

{- Desugar type class and type class instance declarations

--

-- Type classes become newtypes for their dictionaries, and type instances become dictionary declarations.

-- Additional values are generated to access individual members of a dictionary, with the appropriate type.

--

-- E.g. the following

--

-- module Test where

--

-- class Foo a where

-- foo :: a -> a

--

-- instance fooString :: Foo String where

-- foo s = s ++ s

--

-- instance fooArray :: (Foo a) => Foo [a] where

-- foo = map foo

--

-- {- Superclasses -}

--

-- class (Foo a) <= Sub a where

-- sub :: a

--

-- instance subString :: Sub String where

-- sub = ""

--

-- becomes:

--

-- <TypeClassDeclaration Foo ...>

--

-- newtype Foo$Dict a = Foo$Dict { foo :: a -> a }

--

-- -- this following type is marked as not needing to be checked so a new Abs

-- -- is not introduced around the definition in type checking, but when

-- -- called the dictionary value is still passed in for the `dict` argument

-- foo :: forall a. (Foo$Dict a) => a -> a

-- foo (Foo$Dict dict) = dict.foo

--

-- fooString :: Foo$Dict String

-- fooString = Foo$Dict { foo: \s -> s ++ s }

--

-- fooArray :: forall a. (Foo$Dict a) => Foo$Dict [a]

-- fooArray = Foo$Dict { foo: map foo }

--

-- {- Superclasses -}

--

-- <TypeClassDeclaration Sub ...>

--

-- newtype Sub$Dict a = Sub$Dict { sub :: a

-- , "Foo0" :: {} -> Foo$Dict a

-- }

--

-- -- As with `foo` above, this type is unchecked at the declaration

-- sub :: forall a. (Sub$Dict a) => a

-- sub (Sub$Dict dict) = dict.sub

--

-- subString :: Sub$Dict String

-- subString = Sub$Dict { sub: "",

-- , "Foo0": \_ -> <DeferredDictionary Foo String>

-- }

--

-- and finally as the generated javascript:

--

-- var foo = function (dict) {

-- return dict.foo;

-- };

--

-- var fooString = {

-- foo: function (s) {

-- return s + s;

-- }

-- };

--

-- var fooArray = function (dictFoo) {

-- return {

-- foo: map(foo(dictFoo))

-- };

-- };

--

-- var sub = function (dict) {

-- return dict.sub;

-- };

--

-- var subString = {

-- sub: "",

-- Foo0: function () {

-- return fooString;

-- }

-- };

-}

desugarDecl

:: (MonadSupply m, MonadError MultipleErrors m)

=> ModuleName

-> [DeclarationRef]

-> Declaration

-> Desugar m (Maybe DeclarationRef, [Declaration])

desugarDecl mn exps = go

where

go d@(TypeClassDeclaration sa name args implies deps members) = do

modify (M.insert (mn, name) (makeTypeClassData args (map memberToNameAndType members) implies deps False))

return (Nothing, d : typeClassDictionaryDeclaration sa name args implies members : map (typeClassMemberToDictionaryAccessor mn name args) members)

go (TypeInstanceDeclaration sa na chainId idx name deps className tys body) = do

name' <- desugarInstName name

let d = TypeInstanceDeclaration sa na chainId idx (Right name') deps className tys body

let explicitOrNot = case body of

DerivedInstance -> Left $ DerivedInstancePlaceholder className KnownClassStrategy

NewtypeInstance -> Left $ DerivedInstancePlaceholder className NewtypeStrategy

ExplicitInstance members -> Right members

dictDecl <- case explicitOrNot of

Right members

| className == C.Coercible ->

throwError . errorMessage' (fst sa) $ InvalidCoercibleInstanceDeclaration tys

| otherwise -> do

desugared <- desugarCases members

typeInstanceDictionaryDeclaration sa name' mn deps className tys desugared

Left dict ->

let

dictTy = foldl srcTypeApp (srcTypeConstructor (fmap (coerceProperName . dictTypeName) className)) tys

constrainedTy = quantify (foldr srcConstrainedType dictTy deps)

in

return $ ValueDecl sa name' Private [] [MkUnguarded (TypedValue True dict constrainedTy)]

return (expRef name' className tys, [d, dictDecl])

go other = return (Nothing, [other])

-- Completes the name generation for type class instances that do not have

-- a unique name defined in source code.

desugarInstName :: MonadSupply m => Either Text Ident -> Desugar m Ident

desugarInstName = either freshIdent pure

expRef :: Ident -> Qualified (ProperName 'ClassName) -> [SourceType] -> Maybe DeclarationRef

expRef name className tys

| isExportedClass className && all (all isExportedType . getConstructors) tys =

Just $ TypeInstanceRef genSpan name UserNamed

| otherwise = Nothing

isExportedClass :: Qualified (ProperName 'ClassName) -> Bool

isExportedClass = isExported (elem . TypeClassRef genSpan)

isExportedType :: Qualified (ProperName 'TypeName) -> Bool

isExportedType = isExported $ \pn -> isJust . find (matchesTypeRef pn)

isExported

:: (ProperName a -> [DeclarationRef] -> Bool)

-> Qualified (ProperName a)

-> Bool

isExported test (Qualified (ByModuleName mn') pn) = mn /= mn' || test pn exps

isExported _ _ = internalError "Names should have been qualified in name desugaring"

matchesTypeRef :: ProperName 'TypeName -> DeclarationRef -> Bool

matchesTypeRef pn (TypeRef _ pn' _) = pn == pn'

matchesTypeRef _ _ = False

getConstructors :: SourceType -> [Qualified (ProperName 'TypeName)]

getConstructors = everythingOnTypes (++) getConstructor

where

getConstructor (TypeConstructor _ tcname) = [tcname]

getConstructor _ = []

genSpan :: SourceSpan

genSpan = internalModuleSourceSpan "<generated>"

memberToNameAndType :: Declaration -> (Ident, SourceType)

memberToNameAndType (TypeDeclaration td) = unwrapTypeDeclaration td

memberToNameAndType _ = internalError "Invalid declaration in type class definition"

typeClassDictionaryDeclaration

:: SourceAnn

-> ProperName 'ClassName

-> [(Text, Maybe SourceType)]

-> [SourceConstraint]

-> [Declaration]

-> Declaration

typeClassDictionaryDeclaration sa name args implies members =

let superclassTypes = superClassDictionaryNames implies `zip`

[ function unit (foldl srcTypeApp (srcTypeConstructor (fmap (coerceProperName . dictTypeName) superclass)) tyArgs)

| (Constraint _ superclass _ tyArgs _) <- implies

]

members' = map (first runIdent . memberToNameAndType) members

mtys = members' ++ superclassTypes

toRowListItem (l, t) = srcRowListItem (Label $ mkString l) t

ctor = DataConstructorDeclaration sa (coerceProperName $ dictTypeName name)

[(Ident "dict", srcTypeApp tyRecord $ rowFromList (map toRowListItem mtys, srcREmpty))]

in DataDeclaration sa Newtype (coerceProperName $ dictTypeName name) args [ctor]

typeClassMemberToDictionaryAccessor

:: ModuleName

-> ProperName 'ClassName

-> [(Text, Maybe SourceType)]

-> Declaration

-> Declaration

typeClassMemberToDictionaryAccessor mn name args (TypeDeclaration (TypeDeclarationData sa@(ss, _) ident ty)) =

let className = Qualified (ByModuleName mn) name

dictIdent = Ident "dict"

dictObjIdent = Ident "v"

ctor = ConstructorBinder ss (coerceProperName . dictTypeName <$> className) [VarBinder ss dictObjIdent]

acsr = Accessor (mkString $ runIdent ident) (Var ss (Qualified ByNullSourcePos dictObjIdent))

visibility = second (const TypeVarVisible) <$> args

in ValueDecl sa ident Private []

[MkUnguarded (

TypedValue False (Abs (VarBinder ss dictIdent) (Case [Var ss $ Qualified ByNullSourcePos dictIdent] [CaseAlternative [ctor] [MkUnguarded acsr]])) $

addVisibility visibility (moveQuantifiersToFront NullSourceAnn (quantify (srcConstrainedType (srcConstraint className [] (map (srcTypeVar . fst) args) Nothing) ty)))

)]

typeClassMemberToDictionaryAccessor _ _ _ _ = internalError "Invalid declaration in type class definition"

unit :: SourceType

unit = srcTypeApp tyRecord srcREmpty

typeInstanceDictionaryDeclaration

:: forall m

. MonadError MultipleErrors m

=> SourceAnn

-> Ident

-> ModuleName

-> [SourceConstraint]

-> Qualified (ProperName 'ClassName)

-> [SourceType]

-> [Declaration]

-> Desugar m Declaration

typeInstanceDictionaryDeclaration sa@(ss, _) name mn deps className tys decls =

rethrow (addHint (ErrorInInstance className tys)) $ do

m <- get

-- Lookup the type arguments and member types for the type class

TypeClassData{..} <-

maybe (throwError . errorMessage' ss . UnknownName $ fmap TyClassName className) return $

M.lookup (qualify mn className) m

-- Replace the type arguments with the appropriate types in the member types

let memberTypes = map (second (replaceAllTypeVars (zip (map fst typeClassArguments) tys)) . tuple3To2) typeClassMembers

let declaredMembers = S.fromList $ mapMaybe declIdent decls

-- Instance declarations with a Fail constraint are unreachable code, so

-- we allow them to be empty.

let unreachable = any ((C.Fail ==) . constraintClass) deps && null decls

unless unreachable $

case filter (\(ident, _) -> not $ S.member ident declaredMembers) memberTypes of

hd : tl -> throwError . errorMessage' ss $ MissingClassMember (hd NEL.:| tl)

[] -> pure ()

-- Create values for the type instance members

members <- zip (map typeClassMemberName decls) <$> traverse (memberToValue memberTypes) decls

-- Create the type of the dictionary

-- The type is a record type, but depending on type instance dependencies, may be constrained.

-- The dictionary itself is a record literal (unless unreachable, in which case it's undefined).

superclassesDicts <- for typeClassSuperclasses $ \(Constraint _ superclass _ suTyArgs _) -> do

let tyArgs = map (replaceAllTypeVars (zip (map fst typeClassArguments) tys)) suTyArgs

pure $ Abs (VarBinder ss UnusedIdent) (DeferredDictionary superclass tyArgs)

let superclasses = superClassDictionaryNames typeClassSuperclasses `zip` superclassesDicts

let props = Literal ss $ ObjectLiteral $ map (first mkString) (members ++ superclasses)

dictTy = foldl srcTypeApp (srcTypeConstructor (fmap (coerceProperName . dictTypeName) className)) tys

constrainedTy = quantify (foldr srcConstrainedType dictTy deps)

dict = App (Constructor ss (fmap (coerceProperName . dictTypeName) className)) props

mkTV = if unreachable then TypedValue False (Var nullSourceSpan C.I_undefined) else TypedValue True dict

result = ValueDecl sa name Private [] [MkUnguarded (mkTV constrainedTy)]

return result

where

memberToValue :: [(Ident, SourceType)] -> Declaration -> Desugar m Expr

memberToValue tys' (ValueDecl (ss', _) ident _ [] [MkUnguarded val]) = do

_ <- maybe (throwError . errorMessage' ss' $ ExtraneousClassMember ident className) return $ lookup ident tys'

return val

memberToValue _ _ = internalError "Invalid declaration in type instance definition"

declIdent :: Declaration -> Maybe Ident

declIdent (ValueDeclaration vd) = Just (valdeclIdent vd)

declIdent (TypeDeclaration td) = Just (tydeclIdent td)

declIdent _ = Nothing

typeClassMemberName :: Declaration -> Text

typeClassMemberName = maybe (internalError "typeClassMemberName: Invalid declaration in type class definition") runIdent . declIdent

superClassDictionaryNames :: [Constraint a] -> [Text]

superClassDictionaryNames supers =

[ superclassName pn index

| (index, Constraint _ pn _ _ _) <- zip [0..] supers

]

tuple3To2 :: (a, b, c) -> (a, b)

tuple3To2 (a, b, _) = (a, b)