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Showing content from http://hackage.haskell.org/packages/archive/base/4.6.0.0/doc/html/Data-Dynamic.html below:

Data.Dynamic

Data.Dynamic

Contents

• The Dynamic type
• Converting to and from Dynamic
• Applying functions of dynamic type

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

module Data.Typeable

data Dynamic Source

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).

Showing a value of type Dynamic returns a pretty-printed representation of the object's type; useful for debugging.

Instances

toDyn :: Typeable a => a -> DynamicSource

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)

fromDynSource

Arguments

the dynamically-typed object

a default value

returns: the value of the first argument, if it has the correct type, otherwise the value of the second argument.

Converts a Dynamic object back into an ordinary Haskell value of the correct type. See also fromDynamic.

fromDynamicSource

Arguments

the dynamically-typed object

returns: Just a, if the dynamically-typed object has the correct type (and a is its value), or Nothing otherwise.

Converts a Dynamic object back into an ordinary Haskell value of the correct type. See also fromDyn.

dynApply :: Dynamic -> Dynamic -> Maybe DynamicSource

dynApp :: Dynamic -> Dynamic -> DynamicSource

dynTypeRep :: Dynamic -> TypeRepSource

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