Data.Dynamic (original) (raw)
Contents
Description
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.
Synopsis
- module Data.Typeable
- data Dynamic
- toDyn :: Typeable a => a -> Dynamic
- fromDyn :: Typeable a => Dynamic -> a -> a
- fromDynamic :: Typeable a => Dynamic -> Maybe a
- dynApply :: Dynamic -> Dynamic -> Maybe Dynamic
- dynApp :: Dynamic -> Dynamic -> Dynamic
- dynTypeRep :: Dynamic -> TypeRep
Documentation
The Dynamic type
data Dynamic Source
A value of type [Dynamic](Data-Dynamic.html#t:Dynamic) is an object encapsulated together with its type.
A [Dynamic](Data-Dynamic.html#t:Dynamic) may only represent a monomorphic value; an attempt to create a value of type [Dynamic](Data-Dynamic.html#t:Dynamic) from a polymorphically-typed expression will result in an ambiguity error (see [toDyn](Data-Dynamic.html#v:toDyn)).
[Show](Text-Show.html#t:Show)ing a value of type [Dynamic](Data-Dynamic.html#t:Dynamic) returns a pretty-printed representation of the object's type; useful for debugging.
Converting to and from Dynamic
toDyn :: Typeable a => a -> DynamicSource
Converts an arbitrary value into an object of type [Dynamic](Data-Dynamic.html#t:Dynamic).
The type of the object must be an instance of [Typeable](Data-Typeable-Internal.html#t:Typeable), which ensures that only monomorphically-typed objects may be converted to[Dynamic](Data-Dynamic.html#t:Dynamic). To convert a polymorphic object into [Dynamic](Data-Dynamic.html#t:Dynamic), give it a monomorphic type signature. For example:
toDyn (id :: Int -> Int)fromDynSource
Arguments
| :: 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. |
Converts a [Dynamic](Data-Dynamic.html#t:Dynamic) object back into an ordinary Haskell value of the correct type. See also [fromDynamic](Data-Dynamic.html#v:fromDynamic).