[Haskell-cafe] Use cases of empty type classes
mitchellwrosen at gmail.com
Thu Mar 10 18:42:05 UTC 2016
One empty typeclass I use often not only has no methods, but also has no
This is useful in type families that return Constraint, when you want to
say this constraint is "unsatisfiable". I suppose returning something like
"True ~ False" would also suffice, but isn't as pretty.
On Monday, March 7, 2016 at 10:10:48 PM UTC-8, Tomas Tauber wrote:
> Hi everyone,
> I have one question. What are current use cases of type classes with no
> I saw early uses in type-level programming (e.g. HList ).
> In the OO world, interfaces with no methods are called marker interfaces
> -- their use cases range from things that could be done with datatype
> generic programming in Haskell (e.g. serialization) to metadata annotations
> (e.g. RandomAccess ).
> Tomas Tauber
>  http://okmij.org/ftp/Haskell/HList-ext.pdf
>  https://docs.oracle.com/javase/8/docs/api/java/util/RandomAccess.html
> Haskell-Cafe mailing list
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