Hi, I've proposed something like this in the past (which was rightfully rejected). You may be interested in the discussion here: https://github.com/ghc-proposals/ghc-proposals/pull/22 Sylvain On 12/07/2021 20:24, Lana Black wrote:
Hello cafe,
Is it possible in Haskell to check a lack of a certain constraint?
For example,
``` foo :: C => a foo = undefined
```
Here `foo` can only be compiled if called with C satisfied. How do I write the opposite, so that `foo` is only possible to use when C is not satisfied?
With best regards.
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