Safe Haskell	Safe-Inferred
Language	Haskell2010

Data.Binary.Typed.Internal

Contents

Typed
TypeRep
TyCon

Description

Internals, exposed mostly for potential use by testsuites and benchmarks.

Not recommended to be used from within other independent libraries.

Synopsis

`Typed`

data Typed a Source

A value suitable to be typechecked using the contained extra type information.

Constructors

Typed TypeInformation a

Using this data constructor directly is unsafe, as it allows construction of ill-typed Typed data. Use the typed smart constructor unless you really need Typed.

Instances

Show a => Show (Typed a)	"typed <format> <value>"
(Binary a, Typeable * a) => Binary (Typed a)	Ensures data is decoded as the appropriate type with high or total confidence (depending on with what `TypeFormat` the `Typed` was constructed).

data TypeInformation Source

Type information stored alongside a value to be serialized, so that the recipient can do consistency checks. See TypeFormat for more detailed information on the fields.

Constructors

Untyped'
Hashed' Hash
Shown' Hash String
Full' TypeRep
Cached' ByteString

Instances

Eq TypeInformation
Ord TypeInformation
Show TypeInformation
Generic TypeInformation
Binary TypeInformation
type Rep TypeInformation

newtype Hash Source

A hash value of a TypeRep. Currently a 64-bit value created using the MurmurHash2 algorithm.

Constructors

Hash Word64

Instances

Eq Hash
Ord Hash
Show Hash
Generic Hash
Binary Hash
type Rep Hash

typed :: Typeable a => TypeFormat -> a -> Typed a Source

Construct a Typed value using the chosen type format.

Example:

value = typed Full ("hello", 1 :: Int, 2.34 :: Double)
encded = encode value

The decode site can now verify whether decoding happens with the right type.

data TypeFormat Source

Different ways of including/verifying type information of serialized messages.

Constructors

Untyped	Include no type information. Requires one byte more than using `Binary` directly (namely to tag the data as untyped, required for the decoding step).
Hashed	Compare types by their hash values (using the MurmurHash2 algorithm). Requires only 8 additional bytes for the type information. Subject to false positive due to hash collisions, although in practice this should almost never happen. Type errors cannot tell the provided type ("Expected X, received type with hash H")
Shown	Compare `String` representation of types, obtained by calling `show` on the `TypeRep`, and also include a hash value (like `Hashed`). The former is mostly for readable error messages, the latter provides collision resistance. Data size larger than `Hashed`, but usually smaller than `Full`. Both the hash and the shown type must match to satisfy the typechecker. Useful type errors ("expected X, received Y"). All types are shown unqualified though, making `Foo.X` and `Bar.X` look identical in error messages.
Full	Compare the full representation of a data type. More verbose than `Hashed` and `Shown`. As a rule of thumb, transmitted data is roughly the same as `Shown`, but all names are fully qualified (package, module, type name). Correct comparison (no false positives). An semi-exception here is when types change between package versions: `package-1.0 Foo.X` and `package-1.1 Foo.X` count as the same type. Useful type errors ("expected X, received Y"). All types are shown unqualified though, making `Foo.X` and `Bar.X` look identical in error messages.

Instances

Eq TypeFormat
Ord TypeFormat
Show TypeFormat

getFormat :: TypeInformation -> TypeFormat Source

Extract which TypeFormat was used to create a certain TypeInformation.

typecheck :: Typeable a => Typed a -> Either String (Typed a) Source

Typecheck a Typed. Returns the (well-typed) input, or an error message if the types don't work out.

erase :: Typed a -> a Source

Extract the value of a Typed, i.e. strip off the explicit type information.

This function is safe to use for all Typed values created by the public API, since all construction sites ensure the actual type matches the contained type description.

erase (typed format x) == x

precache :: Typed a -> Typed a Source

Calculate the serialization of a TypeInformation and store it in a Typed value so it does not have to be recalculated on every call to encode.

This is typically applied to a dummy value created using typed and the desired TypeFormat; the actual data is then inserted using reValue, which is how encodeTyped works.