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{-# LANGUAGE CPP #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE PatternGuards #-}
{-# LANGUAGE TupleSections #-}
{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE LambdaCase #-}
-- | Generate presentations for types.
module Present
(-- * Presenting functions
presentIt
,presentName
,presentType
-- * Presentation mediums
,toShow
,toWHNF
,whnfJson
-- * Debugging convenience functions
,presentShow
-- * Types
,Value(..)
,WHNF(..)
-- * Customization classes
,Present0(..)
,Present1(..)
,Present2(..)
,Present3(..)
,Present4(..)
,Present5(..)
,Present6(..))
where
import Control.Arrow (second)
import Control.Exception (evaluate,SomeException(..),try,evaluate)
import Control.Monad (forM)
import Control.Monad.Trans.State.Strict (evalStateT,get,modify,StateT(..))
import Data.Char (isSpace,ord,isAlphaNum)
import Data.Int (Int8,Int16,Int32,Int64)
import Data.List (nub,find,intercalate,foldl',isSuffixOf)
import Data.Maybe (mapMaybe,isJust)
import Data.Ratio (numerator,denominator)
import Data.String (IsString)
import Data.Typeable (typeOf)
import Data.Word (Word8,Word32,Word64)
import Foreign.ForeignPtr
import Foreign.Ptr
import Numeric (showHex)
import System.IO.Unsafe (unsafePerformIO)
import Text.Printf (printf)
import qualified Language.Haskell.TH as TH
import qualified Language.Haskell.TH.Syntax as TH
--------------------------------------------------------------------------------
-- Introduction
--
-- Present's algorithm works in stages/levels of work. The first
-- implementation of Present worked, but was a mess. This
-- implementation is an effort to separate all that functionality into
-- clean, small stages.
--------------------------------------------------------------------------------
-- Type Normalization
--
-- TH's representation of types is wider than what Present cares
-- about, and has some heterogeneity that is unwanted; it adds some
-- messiness. To simplify the code further down, we perform this
-- transformation to simplify the types and therefore the scope we
-- have to deal with.
--
-- TH's representation of names is also unfortunate, as it mixes up
-- variables, types and type variables all together. We address that
-- too.
-- | A type variable.
newtype TypeVariable =
TypeVariable TH.Name
deriving (Eq)
-- | A type constructor.
newtype TypeConstructor =
TypeConstructor TH.Name
deriving (Eq)
-- | A primitive type constructor.
newtype PrimitiveTypeConstructor =
PrimitiveTypeConstructor TH.Name
-- | A normalized type.
data NormalType
= NormalCons TypeConstructor
| NormalPrimitive PrimitiveTypeConstructor
| NormalFunction TH.Type
| NormalVar TypeVariable
| NormalApp NormalType
[NormalType]
-- | Convert the heterogenous TH type into a more normal form.
normalizeType
:: TH.Type -> Either String NormalType
normalizeType = go
where go =
\case
ty@TH.AppT{} ->
do let (typeFunction,typeArguments) = flattenApplication ty
case typeFunction of
TH.ArrowT -> return (NormalFunction ty)
_ -> NormalApp <$> go typeFunction <*> mapM go typeArguments
TH.ForallT _ context ty ->
if isFunction ty
then return (NormalFunction ty)
else go (typeClassDefaulting context ty)
TH.SigT ty _kind -> go ty
TH.VarT name -> return (NormalVar (TypeVariable name))
TH.ConT name ->
return (if isPrimitiveType name
then NormalPrimitive (PrimitiveTypeConstructor name)
else NormalCons (TypeConstructor name))
TH.TupleT i ->
case lookup i tupleConstructors of
Nothing -> Left ("Tuple arity " ++ show i ++ " not supported.")
Just cons -> return (NormalCons (TypeConstructor cons))
TH.ListT -> return (NormalCons (TypeConstructor ''[]))
TH.PromotedT _ -> Left "Promoted types are not supported."
TH.UnboxedTupleT _ -> Left "Unboxed tuples are not supported."
TH.ArrowT -> Left "The function arrow (->) is not supported."
TH.EqualityT -> Left "Equalities are not supported."
TH.PromotedTupleT _ -> Left "Promoted types are not supported."
TH.PromotedNilT -> Left "Promoted types are not supported."
TH.PromotedConsT -> Left "Promoted types are not supported."
TH.StarT -> Left "Star (*) is not supported."
TH.ConstraintT -> Left "Constraints are not supported."
TH.LitT _ -> Left "Type-level literals are not supported."
#if MIN_VERSION_template_haskell(2,11,0)
TH.InfixT{} -> Left "Infix type constructors are not supported."
TH.UInfixT{} -> Left "Unresolved infix type constructors are not supported."
TH.ParensT _ -> Left "Parenthesized types are not supported."
TH.WildCardT -> Left "Wildcard types are not supported."
#endif
-- | Is the type a function?
isFunction :: TH.Type -> Bool
isFunction ty =
let (typeFunction,_) = flattenApplication ty
in case typeFunction of
TH.ArrowT -> True
_ -> False
-- | Arity-constructor mapping for tuples.
tupleConstructors :: [(Int,TH.Name)]
tupleConstructors =
[(0,''())
,(2,''(,))
,(3,''(,,))
,(4,''(,,,))
,(5,''(,,,,))
,(6,''(,,,,,))
,(7,''(,,,,,,))
,(8,''(,,,,,,,))
,(9,''(,,,,,,,,))
,(10,''(,,,,,,,,,))
,(11,''(,,,,,,,,,,))
,(12,''(,,,,,,,,,,,))
,(13,''(,,,,,,,,,,,,))
,(14,''(,,,,,,,,,,,,,))
,(15,''(,,,,,,,,,,,,,,))
,(16,''(,,,,,,,,,,,,,,,))
,(17,''(,,,,,,,,,,,,,,,,))
,(18,''(,,,,,,,,,,,,,,,,,))
,(19,''(,,,,,,,,,,,,,,,,,,))
,(20,''(,,,,,,,,,,,,,,,,,,,))
,(21,''(,,,,,,,,,,,,,,,,,,,,))
,(22,''(,,,,,,,,,,,,,,,,,,,,,))
,(23,''(,,,,,,,,,,,,,,,,,,,,,,))
,(24,''(,,,,,,,,,,,,,,,,,,,,,,,))
,(25,''(,,,,,,,,,,,,,,,,,,,,,,,,))
,(26,''(,,,,,,,,,,,,,,,,,,,,,,,,,))]
-- | Is the name specified by Name a primitive type? Like Int#?
--
-- This check may be overly cautious, but it's also about as accurate
-- as one can seemingly be.
isPrimitiveType :: TH.Name -> Bool
isPrimitiveType (TH.Name (TH.OccName _) (TH.NameG TH.TcClsName (TH.PkgName "ghc-prim") (TH.ModName "GHC.Prim"))) =
True
isPrimitiveType name = isSuffixOf "#" (show name)
-- | Flatten a type application f x y into (f,[x,y]).
flattenApplication
:: TH.Type -> (TH.Type,[TH.Type])
flattenApplication = go []
where go args (TH.AppT f x) = go (x : args) f
go args f = (f,args)
--------------------------------------------------------------------------------
-- Defaulting
--
-- For some classes like Num and IsString, we can default to a
-- reasonable value in the REPL. It leads to a better user-experience.
-- | Apply defaulted substitutions for each of the constraints in the
-- type.
typeClassDefaulting
:: [TH.Type] -> TH.Type -> TH.Type
typeClassDefaulting constraints =
applyTypeSubstitution
(mapMaybe (\case
TH.AppT (TH.ConT className) (TH.VarT varName) ->
fmap (\tyName -> (varName,TH.ConT tyName))
(lookup className defaultedClasses)
_ -> Nothing)
constraints)
-- | Apply the given substitutions to the type.
applyTypeSubstitution
:: [(TH.Name,TH.Type)] -> TH.Type -> TH.Type
applyTypeSubstitution subs = go
where go =
\case
TH.ForallT vars ctx ty ->
TH.ForallT vars
ctx
(go ty)
TH.AppT f x ->
TH.AppT (go f)
(go x)
TH.SigT ty k -> TH.SigT (go ty) k
TH.VarT a
| Just b <- lookup a subs -> b
| otherwise -> TH.VarT a
x -> x
-- | Classes which when encountered in a forall context should have
-- their corresponding type variables substituted on the right hand
-- side with the given type.
defaultedClasses :: [(TH.Name,TH.Name)]
defaultedClasses =
[(''Integral,''Integer)
,(''Num,''Integer)
,(''Fractional,''Double)
,(''Bounded,''())
,(''Eq,''())
,(''Read,''())
,(''Show,''())
,(''IsString,''String)]
--------------------------------------------------------------------------------
-- Type Enumeration
--
-- Given a NormalType, we extract all the instances of NormalCons into
-- a flat set.
--
-- We can then run through each type constructor name, reify them, and
-- generate a printer for it. This separate step avoids cycles/acts as
-- an alternative to performing an occurs check.
-- | Enumerate all unique type constructors in the type.
enumerateTypeConstructors
:: NormalType -> [TypeConstructor]
enumerateTypeConstructors = nub . go
where go =
\case
NormalCons cons -> [cons]
NormalApp ty tys -> go ty ++ concatMap go tys
NormalPrimitive{} -> []
NormalVar{} -> []
NormalFunction{} -> []
--------------------------------------------------------------------------------
-- Type Reification
--
-- We have to reify all the type constructors involved in a given
-- type.
--
-- | Name of a variable.
newtype ValueVariable =
ValueVariable TH.Name
-- | Name of a value constructor.
newtype ValueConstructor =
ValueConstructor TH.Name
-- | A normalize representation of a constructor. Present's main
-- algorithm doesn't particularly care whether it's infix, a record,
-- or whatever.
data Constructor =
Constructor {_constructorName :: ValueConstructor
,constructorFields :: [(Maybe ValueVariable,NormalType)]}
-- | A data type.
data DataType =
DataType {_dataTypeVariables :: [TypeVariable]
,_dataTypeConstructors :: [Constructor]}
-- | A type alias.
data TypeAlias =
TypeAlias {_aliasVariables :: [TypeVariable]
,_aliasType :: NormalType}
-- | Definition of a type.
data TypeDefinition
= DataTypeDefinition TypeConstructor
DataType
| TypeAliasDefinition TypeConstructor
TypeAlias
-- | Reify all the constructors of a name. Unless it's primitive, in
-- which case return nothing.
reifyTypeDefinition
:: TypeConstructor -> TH.Q (Maybe TypeDefinition)
reifyTypeDefinition typeConstructor@(TypeConstructor name) =
do info <- TH.reify name
let result =
case info of
TH.TyConI dec ->
case dec of
#if MIN_VERSION_template_haskell(2,11,0)
TH.DataD _cxt0 _ vars _mkind cons _cxt1 ->
#else
TH.DataD _cxt _ vars cons _deriving ->
#endif
do cs <- concat <$> mapM makeConstructors cons
return (Just (DataTypeDefinition typeConstructor
(DataType (map toTypeVariable vars) cs)))
#if MIN_VERSION_template_haskell(2,11,0)
TH.NewtypeD _cxt0 _ vars _mkind con _cxt1 ->
#else
TH.NewtypeD _cxt _ vars con _deriving ->
#endif
do cs <- makeConstructors con
return (Just (DataTypeDefinition
typeConstructor
(DataType (map toTypeVariable vars)
cs)))
TH.TySynD _ vars ty ->
do ty' <- normalizeType ty
return (Just (TypeAliasDefinition typeConstructor
(TypeAlias (map toTypeVariable vars) ty')))
_ -> Left "Not a supported data type declaration."
TH.PrimTyConI{} -> return Nothing
TH.FamilyI{} -> Left "Data families not supported yet."
_ ->
Left ("Not a supported object, no type inside it: " ++
TH.pprint info)
case result of
Left err -> fail err
Right ok -> return ok
-- | Convert a TH type variable to a normalized type variable.
toTypeVariable :: TH.TyVarBndr -> TypeVariable
toTypeVariable =
\case
TH.PlainTV t -> TypeVariable t
TH.KindedTV t _ -> TypeVariable t
-- | Make a normalized constructor from the more complex TH Con.
makeConstructors
:: TH.Con -> Either String [Constructor]
makeConstructors =
\case
TH.NormalC name slots ->
(:[]) <$> makeConstructor name (mapM makeSlot slots)
TH.RecC name fields ->
(:[]) <$> makeConstructor name (mapM makeField fields)
TH.InfixC t1 name t2 ->
(:[]) <$> makeConstructor name ((\x y -> [x,y]) <$> makeSlot t1 <*> makeSlot t2)
(TH.ForallC _ _ con) ->
makeConstructors con
#if MIN_VERSION_template_haskell(2,11,0)
TH.GadtC names slots _type ->
forM names $ \name ->
makeConstructor name (mapM makeSlot slots)
TH.RecGadtC names fields _type ->
forM names $ \name ->
makeConstructor name (mapM makeField fields)
#endif
where makeConstructor name efields = Constructor (ValueConstructor name) <$> efields
makeSlot (_,ty) = (Nothing,) <$> normalizeType ty
makeField (name,_,ty) =
(Just (ValueVariable name),) <$> normalizeType ty
--------------------------------------------------------------------------------
-- Definition Elaboration
--
-- When reifying a type, we discover that it refers to other types
-- which in turn need to be reified. So to get the total of all types
-- that we're going to want to generate a printer for, we need to
-- recursively elaborate everything all the way down.
--
-- A primitive type definition does not decompose into other types.
-- | Elaborate the types involved in a type definition.
definitionNormalTypes
:: TypeDefinition -> [NormalType]
definitionNormalTypes =
\case
DataTypeDefinition _ (DataType _ cons) ->
concatMap (map snd . constructorFields) cons
TypeAliasDefinition _ (TypeAlias _ ty) -> [ty]
--------------------------------------------------------------------------------
-- Complete Expansion
--
-- Finally, we need a way to, given a type, completely explode that
-- type, and every type inside it, recursively, to produce a finite,
-- unique set of TypeDefinitions.
-- | Expand a type into all the type definitions directly or
-- indirectly related.
normalTypeDefinitions
:: NormalType -> TH.Q [TypeDefinition]
normalTypeDefinitions = flip evalStateT [] . expandNormalType
where expandNormalType =
fmap concat . mapM expandTypeConstructor . enumerateTypeConstructors
expandTypeConstructor typeConstructor =
do seenConstructors <- get
if elem typeConstructor seenConstructors
then return []
else do mtypeDefinition <-
liftQ (reifyTypeDefinition typeConstructor)
case mtypeDefinition of
Nothing -> return []
Just typeDefinition ->
do let normalTypes =
definitionNormalTypes typeDefinition
modify (typeConstructor :)
typeDefinitions <-
fmap concat (mapM expandNormalType normalTypes)
return (typeDefinition : typeDefinitions)
-- | Lift a Q monad into a StateT transformer.
liftQ :: TH.Q a -> StateT s TH.Q a
liftQ m =
StateT (\s ->
do v <- m
return (v,s))
--------------------------------------------------------------------------------
-- Printer Generation
--
-- Given a TypeDefinition, generate a printer for that data type.
data Value
= DataValue String String [Value]
| TypeVariableValue String
| PrimitiveValue String
| FunctionValue String
| CharValue String String
| IntegerValue String String
| ChoiceValue String [(String,Value)]
| RecordValue String String [(String,Value)]
| ListValue String [Value]
| StringValue String String
| TupleValue String [Value]
| ExceptionValue String String
deriving (Show)
-- | Make a presenter for a type definition.
typeDefinitionPresenter :: [(TypeConstructor,ValueVariable)]
-> TypeDefinition
-> TH.Q [TH.Dec]
typeDefinitionPresenter instances =
\case
DataTypeDefinition typeConstructor dataType@(DataType typeVariables _) ->
case find (namesBasicallyEqual typeConstructor . fst) instances of
Nothing ->
case find (namesBasicallyEqual typeConstructor . fst) builtInPresenters of
Nothing -> dataTypePresenter typeConstructor dataType
Just (_,presenter) ->
do automaticPresenter <-
dataTypePresenterBody typeConstructor dataType
builtinFunctionDeclaration typeConstructor
(presenter typeVariables automaticPresenter)
Just (_,methodName) ->
do instanceBasedPresenter typeConstructor methodName dataType typeVariables
TypeAliasDefinition typeConstructor typeAlias ->
typeAliasPresenter typeConstructor typeAlias
-- | Make a printer based on an instance declaration for Present[N].
instanceBasedPresenter :: TypeConstructor
-> ValueVariable
-> DataType
-> [TypeVariable]
-> TH.Q [TH.Dec]
instanceBasedPresenter typeConstructor@(TypeConstructor typeConstructorName) (ValueVariable methodName) dataType typeVariables =
presentingFunctionDeclaration
typeConstructor
typeVariables
(TH.tupE [typeDisplayExpression
,[|\x ->
ChoiceValue
$(typeDisplayExpression)
[("Instance"
,snd $(foldl TH.appE
(TH.varE methodName)
(map (TH.varE . presentVarName) typeVariables))
x)
,("Internal"
,$(dataTypePresenterBody typeConstructor dataType) x)]|]])
where typeDisplayExpression = typeDisplay typeVariables typeConstructorName
-- | Make a presenter for the given data type.
dataTypePresenter
:: TypeConstructor -> DataType -> TH.Q [TH.Dec]
dataTypePresenter typeConstructor@(TypeConstructor typeConstructorName) dataType@(DataType typeVariables _) =
presentingFunctionDeclaration
typeConstructor
typeVariables
(TH.tupE [typeDisplayExpression
,dataTypePresenterBody typeConstructor dataType])
where typeDisplayExpression = typeDisplay typeVariables typeConstructorName
-- | Make a printer for a data type, just the expression part.
dataTypePresenterBody
:: TypeConstructor -> DataType -> TH.Q TH.Exp
dataTypePresenterBody (TypeConstructor typeConstructorName) (DataType typeVariables constructors) =
TH.lamCaseE (map constructorCase constructors)
where typeDisplayExpression = typeDisplay typeVariables typeConstructorName
constructorCase (Constructor (ValueConstructor valueConstructorName) fields) =
TH.match (TH.conP valueConstructorName (map (return . fieldPattern) indexedFields))
(TH.normalB
(TH.appE presentationConstructor (TH.listE (map fieldPresenter indexedFields))))
[]
where presentationConstructor =
if isTuple typeConstructorName
then TH.appE (TH.conE 'TupleValue) typeDisplayExpression
else TH.appE (TH.appE (TH.conE (if any (isJust . fst) fields &&
not (null fields)
then 'RecordValue
else 'DataValue))
typeDisplayExpression)
(TH.litE (TH.stringL (TH.pprint valueConstructorName)))
indexedFields = zip (map indexedFieldName [0 ..]) fields
fieldPattern (indexedName,_) = TH.VarP indexedName
fieldPresenter (indexedName,(mvalueVariable,normalType)) =
addField (TH.appE (TH.appE (TH.varE 'snd)
(expressType typeVariables normalType))
(TH.varE indexedName))
where addField =
case mvalueVariable of
Nothing -> id
Just (ValueVariable fieldName) ->
\e ->
TH.tupE [TH.stringE (TH.pprint fieldName),e]
-- | Generate an expression which displays a data type and its
-- type variables as instantiated.
typeDisplay
:: [TypeVariable] -> TH.Name -> TH.Q TH.Exp
typeDisplay typeVariables name =
(applyToVars . TH.litE . TH.stringL . TH.pprint) name
where applyToVars typeConstructorDisplay
| null typeVariables = typeConstructorDisplay
| isTuple name =
[|("(" ++
intercalate
","
$(TH.listE (map (\typeVariable ->
TH.appE (TH.varE 'fst)
(TH.varE (presentVarName typeVariable)))
typeVariables)) ++
")")|]
| otherwise =
TH.appE (TH.varE 'unwords)
(TH.infixE (Just (TH.listE [typeConstructorDisplay]))
(TH.varE '(++))
(Just (TH.listE (map (\typeVariable ->
TH.appE (TH.varE 'parensIfNeeded)
(TH.appE (TH.varE 'fst)
(TH.varE (presentVarName typeVariable))))
typeVariables))))
-- | Is a name a tuple?
isTuple :: TH.Name -> Bool
isTuple typeConstructorName =
any ((== typeConstructorName) . snd) tupleConstructors
-- | Add parens to a string if there's a space inside.
parensIfNeeded :: [Char] -> [Char]
parensIfNeeded e =
if any isSpace e
then "(" ++ e ++ ")"
else e
-- | Make a name for an indexed field of a data type constructor.
indexedFieldName :: Integer -> TH.Name
indexedFieldName index = TH.mkName ("indexedField_" ++ show index)
-- | Make a printer for a type-alias. This involves simply proxying to
-- the real printer, whether that's a data type or a primitive, or
-- another type-alias.
typeAliasPresenter
:: TypeConstructor -> TypeAlias -> TH.Q [TH.Dec]
typeAliasPresenter typeConstructor@(TypeConstructor typeConstructorName) (TypeAlias typeVariables normalType) =
presentingFunctionDeclaration
typeConstructor
typeVariables
(TH.tupE [TH.litE (TH.stringL (TH.pprint typeConstructorName))
,TH.appE (TH.varE 'snd)
(expressType typeVariables normalType)])
-- | Make a presenting function.
builtinFunctionDeclaration
:: TypeConstructor -> TH.Q TH.Exp -> TH.Q [TH.Dec]
builtinFunctionDeclaration typeConstructor body =
do dec <-
TH.valD (TH.varP name)
(TH.normalB body)
[]
return [dec]
where name = presentConsName typeConstructor
-- | Make a presenting function.
presentingFunctionDeclaration :: TypeConstructor
-> [TypeVariable]
-> TH.Q TH.Exp
-> TH.Q [TH.Dec]
presentingFunctionDeclaration typeConstructor@(TypeConstructor typeConstructorName) typeVariables body =
do sig <-
TH.sigD name
(TH.forallT
(map (\(TypeVariable typeVariable) -> TH.PlainTV typeVariable) typeVariables)
(return [])
(foldl (\inner (TypeVariable typeVariable) ->
let presentTypeVariable =
return (TH.AppT (TH.AppT (TH.TupleT 2)
(TH.ConT ''String))
presenter)
where presenter =
TH.AppT (TH.AppT TH.ArrowT (TH.VarT typeVariable))
(TH.ConT ''Value)
in TH.appT (TH.appT TH.arrowT presentTypeVariable) inner)
tupleType
(reverse typeVariables)))
dec <-
if null typeVariables
then TH.valD (TH.varP name)
(TH.normalB body)
[]
else TH.funD name
[TH.clause (map (\typeVariable ->
TH.varP (presentVarName typeVariable))
typeVariables)
(TH.normalB body)
[]]
return [sig,dec]
where name = presentConsName typeConstructor
tupleType =
((\string typ -> TH.AppT (TH.AppT (TH.TupleT 2) string) typ) <$>
TH.conT ''String <*>
TH.appT (TH.appT TH.arrowT appliedType)
(TH.conT ''Value))
appliedType =
foldl TH.appT
(TH.conT typeConstructorName)
(map (\(TypeVariable typeVariableName) ->
TH.varT typeVariableName)
typeVariables)
--------------------------------------------------------------------------------
-- Built-in printers
-- | Are the names basically equal, disregarding package id buggerances?
namesBasicallyEqual
:: TypeConstructor -> TypeConstructor -> Bool
namesBasicallyEqual (TypeConstructor this) (TypeConstructor that) =
normalize this == normalize that
where normalize n@(TH.Name name flavour) =
case flavour of
TH.NameG _ _ modName -> TH.Name name (TH.NameQ modName)
_ -> n
-- | Printers for built-in data types with custom representations
-- (think: primitives, tuples, etc.)
builtInPresenters
:: [(TypeConstructor,[TypeVariable] -> TH.Exp -> TH.Q TH.Exp)]
builtInPresenters =
concat [listPrinters
,integerPrinters
,realPrinters
,charPrinters
,packedStrings
,vectorPrinters
,pointerPrinters]
-- | Vectors.
vectorPrinters
:: [(TypeConstructor,[TypeVariable] -> TH.Exp -> TH.Q TH.Exp)]
vectorPrinters =
[makeVectorPrinter (qualified "Data.Vector" "Vector")
(qualified "Data.Vector" "toList")]
where makeVectorPrinter typeName unpackFunction =
(TypeConstructor typeName
,\(typeVariable:_) automaticPrinter ->
(let presentVar = TH.varE (presentVarName typeVariable)
in TH.lamE [TH.varP (presentVarName typeVariable)]
[|(let typeString =
$(TH.stringE (TH.pprint typeName)) ++
" " ++ parensIfNeeded (fst $(presentVar))
in (typeString
,\xs ->
ChoiceValue
typeString
[("List"
,ListValue typeString
(map (snd $(presentVar))
($(TH.varE unpackFunction) xs)))
,("Internal",$(return automaticPrinter) xs)]))|]))
qualified modName term =
TH.Name (TH.OccName term)
(TH.NameQ (TH.ModName modName))
-- | Packed strings; Text, ByteString.
--
-- This function cleverly acccess functions from these packages in the
-- code generation, without actually needing the `present' package to
-- depend on them directly.
--
packedStrings
:: [(TypeConstructor,a -> TH.Exp -> TH.Q TH.Exp)]
packedStrings =
[makeStringPrinter (qualified "Data.ByteString.Internal" "ByteString")
(qualified "Data.ByteString.Char8" "unpack")
,makeStringPrinter (qualified "Data.ByteString.Lazy.Internal" "ByteString")
(qualified "Data.ByteString.Lazy.Char8" "unpack")
,makeStringPrinter (qualified "Data.Text.Internal" "Text")
(qualified "Data.Text" "unpack")
,makeStringPrinter (qualified "Data.Text.Internal.Lazy" "Text")
(qualified "Data.Text.Lazy" "unpack")]
where makeStringPrinter typeName unpackFunction =
(TypeConstructor typeName
,\_ internal ->
[|let typeString = $(TH.stringE (TH.pprint typeName))
in (typeString
,\xs ->
ChoiceValue
typeString
[("String"
,StringValue typeString
($(TH.varE unpackFunction) xs))
,("Internal",$(return internal) xs)])|])
qualified modName term =
TH.Name (TH.OccName term)
(TH.NameQ (TH.ModName modName))
-- | Printers for list-like types.
listPrinters
:: [(TypeConstructor,[TypeVariable] -> TH.Exp -> TH.Q TH.Exp)]
listPrinters =
[(TypeConstructor ''[]
,\(typeVariable:_) _automaticPrinter ->
(let presentVar = TH.varE (presentVarName typeVariable)
in TH.lamE [TH.varP (presentVarName typeVariable)]
[|(let typeString = "[" ++ fst $(presentVar) ++ "]"
in (typeString
,\xs ->
ListValue typeString (map (snd $(presentVar)) xs)))|]))]
-- | Printers for character-like types.
charPrinters
:: [(TypeConstructor,a -> TH.Exp -> TH.Q TH.Exp)]
charPrinters = map makeCharPrinter [''Char]
where makeCharPrinter name =
(TypeConstructor name
,\_ automaticPrinter ->
[|($(TH.stringE (show name))
,\c ->
ChoiceValue
$(TH.stringE (show name))
[("Character"
,CharValue $(TH.stringE (show name))
(return c))
,("Unicode point",($(intPrinter Nothing name) (ord c)))
,("Internal",$(return automaticPrinter) c)])|])
-- | Printers for pointer types.
pointerPrinters
:: [(TypeConstructor,[TypeVariable] -> TH.Exp -> TH.Q TH.Exp)]
pointerPrinters = map makePtrPrinter [''Ptr,''ForeignPtr,''FunPtr]
where makePtrPrinter name =
(TypeConstructor name
,\(typeVariable:_) automaticPrinter ->
(let presentVar = TH.varE (presentVarName typeVariable)
in TH.lamE [TH.varP (presentVarName typeVariable)]
[|(let typeString =
$(TH.stringE (show name)) ++
" " ++ parensIfNeeded (fst $(presentVar))
in (typeString
,\x ->
ChoiceValue
typeString
[("Pointer"
,IntegerValue typeString
(show x))
,("Internal",$(return automaticPrinter) x)]))|]))
-- | Printers for real number types.
realPrinters
:: [(TypeConstructor,a -> TH.Exp -> TH.Q TH.Exp)]
realPrinters = map makeIntPrinter [''Float,''Double]
where makeIntPrinter name =
(TypeConstructor name
,\_ automaticPrinter ->
[|($(TH.stringE (show name))
,$(floatingPrinter (Just automaticPrinter)
name))|])
-- | Printers for integral types.
integerPrinters
:: [(TypeConstructor,a -> TH.Exp -> TH.Q TH.Exp)]
integerPrinters =
map makeIntPrinter
[''Integer
,''Int
,''Int8
,''Int16
,''Int32
,''Int64
,''Word
,''Word8
,''Word32
,''Word64]
where makeIntPrinter name =
(TypeConstructor name
,\_ automaticPrinter ->
[|($(TH.stringE (show name))
,$(intPrinter (Just automaticPrinter)
name))|])
-- | Show a rational as x/y.
showRational :: Rational -> String
showRational x = show (numerator x) ++ "/" ++ show (denominator x)
-- | Floating point printer.
floatingPrinter
:: Maybe TH.Exp -> TH.Name -> TH.Q TH.Exp
floatingPrinter mautomaticPrinter name =
[|\x ->
ChoiceValue
$(TH.stringE (show name))
$(case mautomaticPrinter of
Nothing ->
[|[("Floating"
,IntegerValue $(TH.stringE (show name))
(printf "%f" x))
,("Show"
,IntegerValue $(TH.stringE (show name))
(show x))
,("Rational"
,IntegerValue $(TH.stringE (show name))
(showRational (toRational x)))]|]
Just automaticPrinter ->
[|[("Floating"
,IntegerValue $(TH.stringE (show name))
(printf "%f" x))
,("Show"
,IntegerValue $(TH.stringE (show name))
(show x))
,("Rational"
,IntegerValue $(TH.stringE (show name))
(showRational (toRational x)))
,("Internal",$(return automaticPrinter) x)]|])|]
-- | Integer printer.
intPrinter
:: Maybe TH.Exp -> TH.Name -> TH.Q TH.Exp
intPrinter mautomaticPrinter name =
[|\x ->
ChoiceValue
$(TH.stringE (show name))
$(case mautomaticPrinter of
Nothing ->
[|[("Decimal"
,IntegerValue $(TH.stringE (show name))
(show x))
,("Hexadecimal"
,IntegerValue $(TH.stringE (show name))
(Text.Printf.printf "%x" x))
,("Binary"
,IntegerValue $(TH.stringE (show name))
(Text.Printf.printf "%b" x))]|]
Just automaticPrinter ->
[|[("Decimal"
,IntegerValue $(TH.stringE (show name))
(show x))
,("Hexadecimal"
,IntegerValue $(TH.stringE (show name))
(Text.Printf.printf "%x" x))
,("Binary"
,IntegerValue $(TH.stringE (show name))
(Text.Printf.printf "%b" x))
,("Internal",$(return automaticPrinter) x)]|])|]
--------------------------------------------------------------------------------
-- Type Expression
--
-- Given a type, we generate an expression capable of printing that
-- type. It's just a simple translation from type application to
-- function application.
--
-- | Make an expression for presenting a type. This doesn't actually
-- do any unpacking of the data structures pertaining to the types,
-- but rather makes calls to the functions that do.
expressType
:: [TypeVariable] -> NormalType -> TH.Q TH.Exp
expressType = go 0
where go arity typeVariables =
\case
NormalVar ty ->
if elem ty typeVariables
then TH.varE (presentVarName ty)
else return (presentUnknownVar ty arity)
NormalCons cons -> TH.varE (presentConsName cons)
NormalPrimitive (PrimitiveTypeConstructor typeConstructorName) ->
expressPrimitive typeConstructorName
NormalFunction ty ->
return (TH.TupE [TH.LitE (TH.StringL (TH.pprint ty))
,TH.LamE [TH.WildP]
(TH.AppE (TH.ConE 'FunctionValue)
(TH.LitE (TH.StringL (TH.pprint ty))))])
NormalApp f args ->
foldl TH.appE
(go (length args) typeVariables f)
(map (go 0 typeVariables) args)
-- | Express a primitive printer.
expressPrimitive :: TH.Name -> TH.Q TH.Exp
expressPrimitive typeConstructorName =
do info <- TH.reify typeConstructorName
case info of
TH.PrimTyConI _ arity _unlifted ->
return (ignoreTypeVariables
arity
(TH.TupE [TH.LitE (TH.StringL (TH.pprint typeConstructorName))
,TH.LamE [TH.WildP]
(TH.AppE (TH.ConE 'PrimitiveValue)
(TH.LitE (TH.StringL (TH.pprint typeConstructorName))))]))
_ -> fail ("Mistaken primitive type: " ++ TH.pprint typeConstructorName)
-- | Name for a function name for presenting a type variable of a data
-- type.
presentUnknownVar
:: TypeVariable -> Int -> TH.Exp
presentUnknownVar (TypeVariable ty) arity =
ignoreTypeVariables
arity
(TH.TupE [TH.LitE (TH.StringL (TH.pprint ty))
,TH.LamE [TH.WildP]
(TH.AppE (TH.ConE 'TypeVariableValue)
(TH.LitE (TH.StringL (TH.pprint ty))))])
-- | Given the arity, make a lambda of that arity and ignore all the
-- paramters.
ignoreTypeVariables :: Int -> TH.Exp -> TH.Exp
ignoreTypeVariables arity
| arity == 0 = id
| otherwise = TH.ParensE . TH.LamE (replicate arity TH.WildP)
-- | Name for a function name for presenting a type variable of a data
-- type.
presentVarName :: TypeVariable -> TH.Name
presentVarName (TypeVariable ty) =
TH.mkName ("presentVar_" ++ normalizeName ty)
-- | Name for a function name for presenting a type constructor.
presentConsName :: TypeConstructor -> TH.Name
presentConsName (TypeConstructor ty) =
TH.mkName ("presentCons_" ++ normalizeName ty)
-- | Normalize a name into a regular format.
normalizeName :: TH.Name -> String
normalizeName x = concatMap replace (show x)
where replace 'z' = "zz"
replace c
| isAlphaNum c = [c]
| otherwise = "z" ++ printf "%x" (ord c)
--------------------------------------------------------------------------------
-- Extension classes
--
-- Some user-defined data structures might have some specific opaque
-- representations, so having some extension classes for a few of them
-- allows us to provide altnerative representations. If such instances
-- are provided, they will be prefered above the other default
-- printers.
-- | Get a mapping from type to instance methods of instances of
-- Present, Present1, etc.
getPresentInstances
:: TH.Q [(TypeConstructor,ValueVariable)]
getPresentInstances =
do p0 <- getFor ''Present0
p1 <- getFor ''Present1
p2 <- getFor ''Present2
p3 <- getFor ''Present3
p4 <- getFor ''Present4
return (concat [p0,p1,p2,p3,p4])
where getFor cls =
do result <- TH.reify cls
case result of
TH.ClassI (TH.ClassD _ _ _ _ [TH.SigD method _]) instances ->
return (mapMaybe (\i ->
case i of
#if MIN_VERSION_template_haskell(2,11,0)
TH.InstanceD _moverlap _ (TH.AppT (TH.ConT _className) (TH.ConT typeName)) _ ->
#else
TH.InstanceD _ (TH.AppT (TH.ConT _className) (TH.ConT typeName)) _ ->
#endif
Just (TypeConstructor typeName
,ValueVariable method)
_ -> Nothing)
instances)
_ -> return []
class Present0 a where
present0 :: (String,a -> Value)
class Present1 a where
present1
:: (String,x -> Value)
-> (String,a x -> Value)
class Present2 a where
present2
:: (String,x -> Value)
-> (String,y -> Value)
-> (String,a x y -> Value)
class Present3 a where
present3
:: (String,x -> Value)
-> (String,y -> Value)
-> (String,z -> Value)
-> (String,a x y z -> Value)
class Present4 a where
present4
:: (String,x -> Value)
-> (String,y -> Value)
-> (String,z -> Value)
-> (String,z0 -> Value)
-> (String,a x y z z0 -> Value)
class Present5 a where
present5
:: (String,x -> Value)
-> (String,y -> Value)
-> (String,z -> Value)
-> (String,z0 -> Value)
-> (String,z1 -> Value)
-> (String,a x y z z0 z1 -> Value)
class Present6 a where
present6
:: (String,x -> Value)
-> (String,y -> Value)
-> (String,z -> Value)
-> (String,z0 -> Value)
-> (String,z1 -> Value)
-> (String,z2 -> Value)
-> (String,a x y z z0 z1 z2 -> Value)
--------------------------------------------------------------------------------
-- Actual Presenting
--
-- Finally, we take the type of `it' and generate a set of presenters
-- for it and present the value in a self-contained let-expression.
-- | Present whatever in scope is called `it'
presentIt :: TH.Q TH.Exp
presentIt = presentName (TH.mkName "it")
-- | Make a presenter for the name
presentName :: TH.Name -> TH.Q TH.Exp
presentName name =
do result <- tryQ (TH.reify name)
case result of
Nothing -> fail "Name `it' isn't in scope."
#if MIN_VERSION_template_haskell(2,11,0)
Just (TH.VarI _ ty _) ->
#else
Just (TH.VarI _ ty _ _) ->
#endif
TH.appE (presentType (return ty)) (TH.varE name)
_ -> fail "The name `it' isn't a variable."
where tryQ m =
TH.recover (pure Nothing)
(fmap Just m)
-- | Present the value with the given type.
presentType :: TH.Q TH.Type -> TH.Q TH.Exp
presentType getTy =
do ty <- getTy
let normalizeResult = normalizeType ty
case normalizeResult of
Left err -> fail err
Right normalType ->
do instances <- getPresentInstances
typeDefinitions <- normalTypeDefinitions normalType
presenters <-
mapM (typeDefinitionPresenter instances) typeDefinitions
TH.letE (map return (concat presenters))
(TH.infixE (Just (TH.varE 'wrapExceptions))
(TH.varE '(.))
(Just (TH.appE (TH.varE 'snd)
(expressType [] normalType))))
--------------------------------------------------------------------------------
-- Debugging helpers
-- | Present a value and then use 'toShow' on it.
--
-- >>> :t $(presentShow [t|Maybe Int|])
-- $(presentShow [t|Maybe Int|]) :: Maybe Int -> String
presentShow :: TH.Q TH.Type -> TH.Q TH.Exp
presentShow ty = [|toShow False . $(presentType ty)|]
--------------------------------------------------------------------------------
-- Exception handling
--
-- We want to be able to handle exceptions ("bottom") in data
-- structures, which is particular to Haskell, by returning that as a
-- presentation, too. So instead of failing to present a data
-- structure just because it has _|_ in it, let's instead put an
-- ExceptionValue inside it that can be presented to the user
-- in a sensible manner.
-- | Wrap any _|_ in the presentation with an exception handler.
wrapExceptions :: Value -> Value
wrapExceptions = wrap . go
where wrap =
either (\(SomeException exception) ->
ExceptionValue (show (typeOf exception))
(show exception))
id .
trySpoon
go =
\case
DataValue a b ps ->
DataValue a
b
(map wrapExceptions ps)
ChoiceValue ty lps ->
ChoiceValue ty
(map (second wrapExceptions) lps)
RecordValue ty c lps ->
RecordValue ty
c
(map (second wrapExceptions) lps)
ListValue ty ps -> seq ps (ListValue ty (map wrapExceptions ps))
TupleValue ty ps ->
seq ps
(TupleValue ty
(map wrapExceptions ps))
p@(CharValue _ x) -> seqString p x
p@(IntegerValue _ x) -> seqString p x
p@TypeVariableValue{} -> p
p@PrimitiveValue{} -> p
p@FunctionValue{} -> p
p@(StringValue _ x) -> seqString p x
p@ExceptionValue{} -> p
-- | Seq a string.
seqString :: Value -> String -> Value
seqString = foldl' (\presentation x -> seq x presentation)
-- | Try to get a non-bottom value from the @a@, otherwise return the
-- exception.
trySpoon :: a -> Either SomeException a
trySpoon a = unsafePerformIO (try (evaluate a))
--------------------------------------------------------------------------------
-- Value mediums
--
-- A presentation by itself is useless, it has to be presented in a
-- medium.
-- | To a familiar Show-like string.
toShow :: Bool -> Value -> String
toShow qualified =
\case
IntegerValue _ i -> i
ExceptionValue ex display -> "<" ++ ex ++ ": " ++ show display ++ ">"
TypeVariableValue ty -> "<_ :: " ++ ty ++ ">"
CharValue _ c -> "'" ++ c ++ "'"
FunctionValue ty -> "<" ++ unwords (lines ty) ++ ">"
DataValue _type name slots ->
qualify name ++
(if null slots
then ""
else " ") ++
intercalate " "
(map recur slots)
RecordValue _type name fields ->
qualify name ++
" {" ++
intercalate ","
(map showField fields) ++
"}"
where showField (fname,slot) =
qualify fname ++ " = " ++ toShow qualified slot
TupleValue _type slots ->
"(" ++
intercalate ","
(map (toShow qualified) slots) ++
")"
ListValue typ slots ->
if typ == "[GHC.Types.Char]"
then show (concatMap (\case
CharValue _ c -> c
ChoiceValue _ ((_,CharValue _ c):_) -> c
_ -> []) slots)
else "[" ++
intercalate ","
(map (toShow qualified) slots) ++
"]"
PrimitiveValue p -> "<" ++ p ++ ">"
StringValue _ string -> show string
ChoiceValue ty ((_,x):choices) ->
case x of
ExceptionValue{}
| not (null choices) -> toShow qualified (ChoiceValue ty choices)
_ -> toShow qualified x
ChoiceValue _ [] -> "<no presentation choices>"
where recur p
| atomic p = toShow qualified p
| otherwise = "(" ++ toShow qualified p ++ ")"
where atomic =
\case
ListValue{} -> True
IntegerValue{} -> True
CharValue{} -> True
StringValue{} -> True
ChoiceValue ty ((_,x):xs) ->
case x of
ExceptionValue{}
| not (null xs) -> atomic (ChoiceValue ty xs)
_ -> atomic x
DataValue _ _ [] -> True
PrimitiveValue _ -> True
_ -> False
qualify x =
if qualified
then x
else reverse (takeWhile (/= '.') (reverse x))
-- | A presentation of a value up to WHNF.
data WHNF
= DataWHNF String String [(String,[Integer])]
| TypeVariableWHNF String
| PrimitiveWHNF String
| FunctionWHNF String
| CharWHNF String String
| IntegerWHNF String String
| ChoiceWHNF String [(String,[Integer])]
| RecordWHNF String String [(String,String,[Integer])]
| ListConsWHNF String [Integer] [Integer]
| ListEndWHNF String
| StringWHNF String String
| TupleWHNF String [(String,[Integer])]
| ExceptionWHNF String String
deriving (Show)
-- | Produce a presentation of the value to WHNF.
toWHNF :: [Integer] -- ^ Cursor.
-> Value -- ^ Value to cursor into.
-> WHNF -- ^ A WHNF presentation of the value at @cursor@.
toWHNF = go []
where go
:: [Integer] -> [Integer] -> Value -> WHNF
go stack cursor =
\case
DataValue typ name slots ->
case cursor of
(slot:subCursor) ->
case lookup slot (zip [0 ..] slots) of
Nothing -> error "toWHNF: Invalid slot."
Just value -> go (push [slot]) subCursor value
_ ->
DataWHNF typ
name
(zipWith (\index slot ->
(valueType slot,push (cursor ++ [index])))
[0 ..]
slots)
ChoiceValue ty slots ->
case cursor of
(slot:subCursor) ->
case lookup slot (zip [0 ..] slots) of
Nothing -> error "toWHNF: Invalid slot."
Just (_,value) -> go (push [slot]) subCursor value
_ ->
ChoiceWHNF
ty
(zipWith (\index (string,_) ->
(string,push (cursor ++ [index])))
[0 ..]
slots)
RecordValue typ name slots ->
case cursor of
(slot:subCursor) ->
case lookup slot (zip [0 ..] slots) of
Nothing -> error "toWHNF: Invalid slot."
Just (_,value) -> go (push [slot]) subCursor value
_ ->
RecordWHNF
typ
name
(zipWith (\index (fname,slot) ->
(valueType slot,fname,push (cursor ++ [index])))
[0 ..]
slots)
ListValue ty slots ->
case cursor of
(slot:subCursor) ->
case slot of
0 ->
case slots of
(value0:_) -> go (push [slot]) subCursor value0
_ -> ListEndWHNF ty
_ ->
case slots of
(_:value1) ->
go (push [slot])
subCursor
(ListValue ty value1)
_ -> ListEndWHNF ty
_ ->
case slots of
[] -> ListEndWHNF ty
(_:_) ->
ListConsWHNF ty
(push cursor ++ [0])
(push cursor ++ [1])
TupleValue ty slots ->
case cursor of
(slot:subCursor) ->
case lookup slot (zip [0 ..] slots) of
Nothing -> error "toWHNF: Invalid slot."
Just value -> go (push [slot]) subCursor value
_ ->
TupleWHNF ty
(zipWith (\index slot ->
(valueType slot
,push (cursor ++ [index])))
[0 ..]
slots)
TypeVariableValue ty -> TypeVariableWHNF ty
PrimitiveValue ty -> PrimitiveWHNF ty
FunctionValue ty -> FunctionWHNF ty
CharValue ty ch -> CharWHNF ty ch
IntegerValue ty rep -> IntegerWHNF ty rep
StringValue ty str -> StringWHNF ty str
ExceptionValue ty c -> ExceptionWHNF ty c
where push xs = stack ++ xs
-- | Get the type of a value.
valueType :: Value -> String
valueType =
\case
DataValue ty _ _ -> ty
TypeVariableValue ty -> ty
PrimitiveValue ty -> ty
FunctionValue ty -> ty
CharValue ty _ -> ty
IntegerValue ty _ -> ty
ChoiceValue ty _ -> ty
RecordValue ty _ _ -> ty
ListValue ty _ -> ty
StringValue ty _ -> ty
TupleValue ty _ -> ty
ExceptionValue ty _ -> ty
-- | Make JSON from WNHF.
whnfJson :: WHNF -> String
whnfJson =
\case
DataWHNF ty name slots ->
jsonObject
[("constructor",jsonString "data")
,("type",jsonString ty)
,("name",jsonString name)
,("slots"
,jsonList (map (\(typ,sid) ->
jsonObject
[("type",jsonString typ)
,("id",jsonList (map jsonInteger sid))])
slots))]
TypeVariableWHNF var ->
jsonObject
[("constructor",jsonString "type-variable"),("type",jsonString var)]
PrimitiveWHNF name ->
jsonObject
[("constructor",jsonString "primitive"),("type",jsonString name)]
FunctionWHNF ty ->
jsonObject [("constructor",jsonString "primitive"),("type",jsonString ty)]
CharWHNF ty string ->
jsonObject
[("constructor",jsonString "char")
,("type",jsonString ty)
,("string",jsonString string)]
IntegerWHNF ty string ->
jsonObject
[("constructor",jsonString "integer")
,("type",jsonString ty)
,("string",jsonString string)]
ChoiceWHNF ty slots ->
jsonObject
[("constructor",jsonString "choice")
,("type",jsonString ty)
,("slots"
,jsonList (map (\(typ,sid) ->
jsonObject
[("title",jsonString typ)
,("id",jsonList (map jsonInteger sid))])
slots))]
RecordWHNF ty name slots ->
jsonObject
[("constructor",jsonString "record")
,("type",jsonString ty)
,("name",jsonString name)
,("slots"
,jsonList (map (\(typ,name',sid) ->
jsonObject
[("type",jsonString typ)
,("name",jsonString name')
,("id",jsonList (map jsonInteger sid))])
slots))]
ListConsWHNF typ x xs ->
jsonObject
[("constructor",jsonString "list-cons")
,("type",jsonString typ)
,("car",jsonList (map jsonInteger x))
,("cdr",jsonList (map jsonInteger xs))]
ListEndWHNF typ ->
jsonObject [("constructor",jsonString "list-end"),("type",jsonString typ)]
StringWHNF typ string ->
jsonObject
[("constructor",jsonString "string")
,("type",jsonString typ)
,("string",jsonString string)]
TupleWHNF ty slots ->
jsonObject
[("constructor",jsonString "tuple")
,("type",jsonString ty)
,("slots"
,jsonList (map (\(typ,sid) ->
jsonObject
[("type",jsonString typ)
,("id",jsonList (map jsonInteger sid))])
slots))]
ExceptionWHNF typ shown ->
jsonObject
[("constructor",jsonString "exception")
,("type",jsonString typ)
,("string",jsonString shown)]
where jsonString :: String -> String
jsonString = (\x -> "\"" ++ x ++ "\"") . go
where go s1 =
case s1 of
(x:xs)
| x < '\x20' ->
'\\' :
encControl x
(go xs)
('"':xs) -> '\\' : '"' : go xs
('\\':xs) -> '\\' : '\\' : go xs
(x:xs) -> x : go xs
"" -> ""
encControl x xs =
case x of
'\b' -> 'b' : xs
'\f' -> 'f' : xs
'\n' -> 'n' : xs
'\r' -> 'r' : xs
'\t' -> 't' : xs
_
| x < '\x10' -> 'u' : '0' : '0' : '0' : hexxs
| x < '\x100' -> 'u' : '0' : '0' : hexxs
| x < '\x1000' -> 'u' : '0' : hexxs
| otherwise -> 'u' : hexxs
where hexxs = showHex (fromEnum x) xs
jsonObject fields =
"{" ++
intercalate ", "
(map makeField fields) ++
"}"
where makeField (name,value) = jsonString name ++ ": " ++ value
jsonList xs = "[" ++ intercalate ", " xs ++ "]"
jsonInteger :: Integer -> String
jsonInteger = show