> And defining a function that will only accept particular variant is nice This is possible to achieve (or hack your way through, if you will) by parameterizin

> And defining a function that will only accept particular variant is nice This is possible to achieve (or hack your way through, if you will) by parameterizing the type and using a nullary type (a type which is impossible to have) to exclude specific cases of a sum type. In Haskell this would look like this: data Weather a b c = Sunny a | Rainy b | Snowy c -- can't snow in the summer! onlySummerWeather :: forall a b. Weather a b Void -> String onlySummerWeather weather = case weather of Sunny _ -> "Got sunny weather" Rainy _ -> "Got rainy weather" Snowy v -> absurd v where `absurd :: forall a. Void -> a` "if you give me something you can't ever have, I will give you anything in return".