{-# LANGUAGE Trustworthy #-}{-# LANGUAGE NoImplicitPrelude #-}{-# LANGUAGE GADTs #-}{-# LANGUAGE ExplicitForAll #-}{-# LANGUAGE PatternSynonyms #-}{-# LANGUAGE ScopedTypeVariables #-}{-# LANGUAGE TypeApplications #-}------------------------------------------------------------------------------- |-- Module : Data.Dynamic-- Copyright : (c) The University of Glasgow 2001-- License : BSD-style (see the file libraries/base/LICENSE)---- Maintainer : libraries@haskell.org-- Stability : experimental-- Portability : portable---- The Dynamic interface provides basic support for dynamic types.---- Operations for injecting values of arbitrary type into-- a dynamically typed value, Dynamic, are provided, together-- with operations for converting dynamic values into a concrete-- (monomorphic) type.-------------------------------------------------------------------------------moduleData.Dynamic(-- * The @Dynamic@ typeDynamic (..),-- * Converting to and from @Dynamic@toDyn ,fromDyn ,fromDynamic ,-- * Applying functions of dynamic typedynApply ,dynApp ,dynTypeRep ,-- * Convenience re-exportsTypeable )whereimportData.Type.Equality importType.Reflection importData.Maybe importGHC.Base importGHC.Show importGHC.Exception ----------------------------------------------------------------- The type Dynamic---------------------------------------------------------------{-|
 A value of type 'Dynamic' is an object encapsulated together with its type.
 A 'Dynamic' may only represent a monomorphic value; an attempt to
 create a value of type 'Dynamic' from a polymorphically-typed
 expression will result in an ambiguity error (see 'toDyn').
 'Show'ing a value of type 'Dynamic' returns a pretty-printed representation
 of the object\'s type; useful for debugging.
-}dataDynamic whereDynamic ::foralla .TypeRep a ->a ->Dynamic -- | @since 2.01instanceShow Dynamic where-- the instance just prints the type representation.showsPrec _(Dynamic t _)=showString "<<". showsPrec 0t . showString ">>"-- here so that it isn't an orphan:-- | @since 4.0.0.0instanceException Dynamic -- Use GHC's primitive 'Any' type to hold the dynamically typed value.---- In GHC's new eval/apply execution model this type must not look-- like a data type. If it did, GHC would use the constructor convention-- when evaluating it, and this will go wrong if the object is really a-- function. Using Any forces GHC to use-- a fallback convention for evaluating it that works for all types.-- | Converts an arbitrary value into an object of type 'Dynamic'.---- The type of the object must be an instance of 'Typeable', which-- ensures that only monomorphically-typed objects may be converted to-- 'Dynamic'. To convert a polymorphic object into 'Dynamic', give it-- a monomorphic type signature. For example:---- > toDyn (id :: Int -> Int)--toDyn::Typeable a =>a ->Dynamic toDyn v =Dynamic typeRep v -- | Converts a 'Dynamic' object back into an ordinary Haskell value of-- the correct type. See also 'fromDynamic'.fromDyn::Typeable a =>Dynamic -- ^ the dynamically-typed object->a -- ^ a default value->a -- ^ returns: the value of the first argument, if-- it has the correct type, otherwise the value of-- the second argument.fromDyn (Dynamic t v )def |Just HRefl <-t `eqTypeRep `typeOf def =v |otherwise =def -- | Converts a 'Dynamic' object back into an ordinary Haskell value of-- the correct type. See also 'fromDyn'.fromDynamic::foralla .Typeable a =>Dynamic -- ^ the dynamically-typed object->Maybe a -- ^ returns: @'Just' a@, if the dynamically-typed-- object has the correct type (and @a@ is its value),-- or 'Nothing' otherwise.fromDynamic (Dynamic t v )|Just HRefl <-t `eqTypeRep `rep =Just v |otherwise =Nothing whererep =typeRep ::TypeRep a -- (f::(a->b)) `dynApply` (x::a) = (f a)::bdynApply::Dynamic ->Dynamic ->Maybe Dynamic dynApply (Dynamic (Fun ta tr )f )(Dynamic ta' x )|Just HRefl <-ta `eqTypeRep `ta' ,Just HRefl <-typeRep @Type`eqTypeRep `typeRepKind tr =Just (Dynamic tr (f x ))dynApply__=Nothing dynApp::Dynamic ->Dynamic ->Dynamic dynApp f x =casedynApply f x ofJust r ->r Nothing ->errorWithoutStackTrace ("Type error in dynamic application.\n"++ "Can't apply function "++ show f ++ " to argument "++ show x )dynTypeRep::Dynamic ->SomeTypeRep dynTypeRep (Dynamic tr _)=SomeTypeRep tr