Yes https://github.com/ghc-proposals/ghc-proposals/pull/387 Implemented in GHC-9.2 - Oleg On 13.12.2021 14.49, Olaf Klinke wrote:
Dear Café,
Question: Is DataKinds promotion of Char values possible, and if yes, how?
I want to define a data type of text where a certain character has special meaning. I could say: data SpecialText = SpecialText Char Text but it would be favourable if the type system forbids combining texts with distinct special characters. data SpecialText char = SpecialText Text Ideally, we could use DataKinds to specialize the char phantom type parameter to a promoted Char value, but neither 'x' nor ''x' is accepted by GHC, presumably for good reasons. After all, 'x' is syntactic sugar for the real constructor of a Char value (which is what? Data.Data.toConstr 'x' yields 'x'.)
One certainly can define data types symbolizing selected single Char values to use as the phantom type, but that means the library author decides which Chars the user can declare as special.
Thanks Olaf
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