You could also pattern-match over them with View Patterns[^1], i.e. export an alternate ADT that is the 'acceptable' view on the data and a function that takes

You could also pattern-match over them with View Patterns[^1], i.e. export an alternate ADT that is the 'acceptable' view on the data and a function that takes the encapsulated implementation and turns it to the alternate representation—but I have literally never seen this done, save in the documents describing the motivations for View Patterns. [^1]: https://ghc.haskell.org/trac/ghc/wiki/ViewPatterns https://ghc.haskell.org/trac/ghc/wiki/ViewPatterns