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'
Hashed5' Hash5
Hashed32' Hash32
Hashed64' Hash64
Shown' Hash32 String
Full' TypeRep
Cached' ByteString

Instances

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

newtype Hash5 Source

A hash value of a TypeRep. Currently a 5-bit value created using the MurmurHash2 algorithm.

Since TypeInformation needs 3 bit to store the sort of the TypeInformation, the remaining 5 bit per Word8 can be used to store a hash value at no additional space cost. For this reason, it is important that the three rightmost bits of any Hashed5 are set to zero.

This type intentionally doesn't have a Binary instance, since its serialization is part of the TypeInformation Binary class exclusively.

Constructors

Hash5 Word8

Instances

Eq Hash5
Ord Hash5
Show Hash5

mkHash5 :: Integral a => a -> Hash5 Source

Smart constructor for Hash5 values. Makes sure the rightmost three bits are not set by applying a bit mask to the input.

newtype Hash32 Source

A hash value of a TypeRep. Currently a 32-bit value created using the MurmurHash2 algorithm.

Constructors

Hash32 Word32

Instances

Eq Hash32
Ord Hash32
Show Hash32
Generic Hash32
Binary Hash32
type Rep Hash32

newtype Hash64 Source

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

Constructors

Hash64 Word64

Instances

Eq Hash64
Ord Hash64
Show Hash64
Generic Hash64
Binary Hash64
type Rep Hash64

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.

makeTypeInformation :: TypeFormat -> TypeRep -> TypeInformation Source

Create the TypeInformation to be stored inside a Typed value from a TypeRep.

data TypeFormat Source

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

Constructors

Untyped	Include no type information. Requires one byte more compared to using `Binary` directly (to tag the data as untyped, required for the decoding step). Encoding and decoding require negligible amount of additional computational cost compared to direct (intrinsically untyped) `Binary`.
Hashed5	Like `Hashed32`, but uses a 5-bit hash value. Requires the same amount of space as `Untyped`, i.e. the only overhead compared to it is the computational cost to calculate the hash, which is almost identical to the one of `Hashed32`. Collisions occur with a probability of 12^5 = 132. For this reason, this format is only recommended when minimal data size is top priority.
Hashed32	Compare types by their hash values (using the MurmurHash2 algorithm). Requires five bytes more compared to using `Binary` directly for the type information (one to tag as `Hashed32`, four for the hash value) 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") Computational cost similar to `Hashed64`.
Hashed64	Like `Hashed32`, but uses a 64-bit hash value. Requires nine bytes more compared to using `Binary`. Hash collisions are even less likely to occur than with `Hashed32`. Computational cost similar to `Hashed32`.
Shown	Compare `String` representation of types, obtained by calling `show` on the `TypeRep`, and also include a hash value (like `Hashed32`). The former is mostly for readable error messages, the latter provides better collision resistance. Data size larger than `Hashed32`, 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. Remember this when you get a seemingly silly error "expected Foo, but given Foo".
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. Remember this when you get a seemingly silly error "expected Foo, but given Foo".

Instances

Eq TypeFormat
Ord TypeFormat
Show TypeFormat

getFormat :: TypeInformation -> TypeFormat Source

Extract which TypeFormat was used to create a certain TypeInformation.

If the type is Cached', then the contained information is assumed well-formed. In the public API, this is safe to do, since only well-typed Typed values can be created in the first place.

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

preserialize :: TypeInformation -> TypeInformation Source

Sometimes it can be beneficial to serialize the type information in advance, so that the maybe costly serialization step does not have to be repeated on every invocation of encode. Preserialization comes at a price though, as the directly contained ByteString requires its length to be included in the final serialization, yielding a 8-byte overhead for the required Int64, and one for the tag of what was serialized ("shown or full?").

This function calculates the serialized version of TypeInformation in cases where the required 9 bytes are negligible (determined by an arbitrary threshold, currently 10*9 bytes).

Used to make encodeTyped more efficient; the source there also makes a good usage example.