[wittystick]

Clean has been doing this for nearly as long as people have been using monads, but it never got the attention Haskell did, which I think is quite unfortunate. Rather than implictly keeping track of references, uniqueness types are marked explicitly to inform that their values cannot be aliased. They can also be used with monads to improve ergonomics a bit.

Granule has uniqueness types like Clean built onto a linear type system, which offers some additional advantages.

[projektfu]

Is Clean being used anywhere? Last time I looked at it was 1999 and, while cool, I haven't ever heard of anyone using it.