Summary
Lawful typeclasses capturing three patterns of bidirectional mapping and forming a layered hierarchy with an ascending strictness of laws.
Smart constructor
Canonicalization or lossy conversion
Isomorphism or lossless conversion
The conversion problem
Have you ever looked for a toString function? How often do you
import Data.Text.Lazy only to call its fromStrict? How
about importing Data.ByteString.Builder only to call its
toLazyByteString and then importing
Data.ByteString.Lazy only to call its toStrict?
Those all are instances of one pattern. They are conversions between different
representations of the same information. Codebases that don't attempt to
abstract over this pattern tend to be sprawling with this type of
boilerplate. It's noise to the codereader, it's a burden to the
implementor and the maintainer.
Why another conversion library?
Many libraries exist that approach the conversion problem. However most of
them provide lawless typeclasses leaving it up to the author of the
instance to define what makes a proper conversion. This results in
inconsistencies across instances, their behaviour not being evident to
the user and no way to check whether an instance is correct.
This library tackles this problem with a lawful typeclass hierarchy, making it
evident what any of its instances do and it provides property-tests for you
to validate your instances.
Prior work and acknowledgements
This library is a direct successor of the "isomorphism-class" library, expanding upon the patterns discovered there. It also shares some ideas with "control-iso" and "type-iso".
