rank1dynamic-0.4.1: Like Data.Dynamic/Data.Typeable but with support for rank-1 polymorphic types

Safe HaskellSafe
LanguageHaskell2010

Data.Rank1Typeable

Contents

Description

Runtime type representation of terms with support for rank-1 polymorphic types with type variables of kind *.

The essence of this module is that we use the standard Typeable representation of Data.Typeable but we introduce a special (empty) data type TypVar which represents type variables. TypVar is indexed by an arbitrary other data type, giving you an unbounded number of type variables; for convenience, we define ANY, ANY1, .., ANY9.

Examples of isInstanceOf
-- We CANNOT use a term of type 'Int -> Bool' as 'Int -> Int'
> typeOf (undefined :: Int -> Int) `isInstanceOf` typeOf (undefined :: Int -> Bool)
Left "Cannot unify Int and Bool"

-- We CAN use a term of type 'forall a. a -> Int' as 'Int -> Int'
> typeOf (undefined :: Int -> Int) `isInstanceOf` typeOf (undefined :: ANY -> Int)
Right ()

-- We CAN use a term of type 'forall a b. a -> b' as 'forall a. a -> a'
> typeOf (undefined :: ANY -> ANY) `isInstanceOf` typeOf (undefined :: ANY -> ANY1)
Right ()

-- We CANNOT use a term of type 'forall a. a -> a' as 'forall a b. a -> b'
> typeOf (undefined :: ANY -> ANY1) `isInstanceOf` typeOf (undefined :: ANY -> ANY)
Left "Cannot unify Succ and Zero"

-- We CAN use a term of type 'forall a. a' as 'forall a. a -> a'
> typeOf (undefined :: ANY -> ANY) `isInstanceOf` typeOf (undefined :: ANY)
Right ()

-- We CANNOT use a term of type 'forall a. a -> a' as 'forall a. a'
> typeOf (undefined :: ANY) `isInstanceOf` typeOf (undefined :: ANY -> ANY)
Left "Cannot unify Skolem and ->"

(Admittedly, the quality of the type errors could be improved.)

Examples of funResultTy
-- Apply fn of type (forall a. a -> a) to arg of type Bool gives Bool
> funResultTy (typeOf (undefined :: ANY -> ANY)) (typeOf (undefined :: Bool))
Right Bool

-- Apply fn of type (forall a b. a -> b -> a) to arg of type Bool gives forall a. a -> Bool
> funResultTy (typeOf (undefined :: ANY -> ANY1 -> ANY)) (typeOf (undefined :: Bool))
Right (ANY -> Bool) -- forall a. a -> Bool

-- Apply fn of type (forall a. (Bool -> a) -> a) to argument of type (forall a. a -> a) gives Bool
> funResultTy (typeOf (undefined :: (Bool -> ANY) -> ANY)) (typeOf (undefined :: ANY -> ANY))
Right Bool

-- Apply fn of type (forall a b. a -> b -> a) to arg of type (forall a. a -> a) gives (forall a b. a -> b -> b)
> funResultTy (typeOf (undefined :: ANY -> ANY1 -> ANY)) (typeOf (undefined :: ANY1 -> ANY1))
Right (ANY -> ANY1 -> ANY1)

-- Cannot apply function of type (forall a. (a -> a) -> a -> a) to arg of type (Int -> Bool)
> funResultTy (typeOf (undefined :: (ANY -> ANY) -> (ANY -> ANY))) (typeOf (undefined :: Int -> Bool))
Left "Cannot unify Int and Bool"
Synopsis

Basic types

data TypeRep Source #

Dynamic type representation with support for rank-1 types

Instances
Eq TypeRep Source # 
Instance details

Defined in Data.Rank1Typeable

Methods

(==) :: TypeRep -> TypeRep -> Bool #

(/=) :: TypeRep -> TypeRep -> Bool #

Show TypeRep Source # 
Instance details

Defined in Data.Rank1Typeable

Binary TypeRep Source # 
Instance details

Defined in Data.Rank1Typeable

Methods

put :: TypeRep -> Put #

get :: Get TypeRep #

putList :: [TypeRep] -> Put #

typeOf :: Typeable a => a -> TypeRep Source #

The type representation of any Typeable term

splitTyConApp :: TypeRep -> (TyCon, [TypeRep]) Source #

Split a type representation into the application of a type constructor and its argument

mkTyConApp :: TyCon -> [TypeRep] -> TypeRep Source #

Inverse of splitTyConApp

Operations on type representations

isInstanceOf :: TypeRep -> TypeRep -> Either TypeError () Source #

t1 isInstanceOf t2 checks if t1 is an instance of t2

funResultTy :: TypeRep -> TypeRep -> Either TypeError TypeRep Source #

funResultTy t1 t2 is the type of the result when applying a function of type t1 to an argument of type t2

type TypeError = String Source #

If isInstanceOf fails it returns a type error

Type variables

data TypVar a Source #

data Succ a Source #

type V0 = Zero Source #

type V1 = Succ V0 Source #

type V2 = Succ V1 Source #

type V3 = Succ V2 Source #

type V4 = Succ V3 Source #

type V5 = Succ V4 Source #

type V6 = Succ V5 Source #

type V7 = Succ V6 Source #

type V8 = Succ V7 Source #

type V9 = Succ V8 Source #

Re-exports from Typeable

class Typeable (a :: k) #

The class Typeable allows a concrete representation of a type to be calculated.

Minimal complete definition

typeRep#