Data.TypeHash

Produce a hash for a type that is unique for that type. The hash takes both actual type names and type structure into account.

The purpose of the hash of a type is to be able to store the type of a persisted value together with the value. By comparing the type hash of a persisted value and the expected value we can know if the persistened value is of the correct type.

The type code preserves the exact structure of the type and can be used to check if one type is a subtype of another. If one type is a subtype of another it means that, e.g., read . show will correctly between the types. (Caveat read . show is only guaranteed to work with named fields.)

The type hash uses a cryptographic hash and can only be used to test equality.

Documentation

data TypeCode

Type codes.

Instances

Eq TypeCode

Data TypeCode

Ord TypeCode

Show TypeCode

Typeable TypeCode

typeCode :: Data a => a -> TypeCode

Turn the type of the value into a type code.

convertibleTo :: TypeCode -> TypeCode -> Bool

Is the first type (code) as subtype of the second, i.e., can the first type be converted to the second.

data TypeHash

Type hash.

Instances

Eq TypeHash

Data TypeHash

Ord TypeHash

Read TypeHash

Show TypeHash

Typeable TypeHash

typeHash :: Data a => a -> TypeHash

Turn the type of the value into a type hash.