Hi Alexey,
I think that if `::=` was used instead of `=` in `data` and `newtype` definitions, this would suggest to a newcomer that the syntax of the two sides might be different, and would helpfully remind of the Backus–Naur Form for syntax rules. I think that a newcomer to Haskell, like myself, would have had a better chance of guessing the meaning of
type Name = String data Date ::= Date Int Int Int data Anniversary ::= Birthday Name Date | Wedding Name Name Date
there is already an alternative syntax for declaring datatypes: data Date where Date :: Int -> Int -> Int -> Date data Anniversary where Birthday :: Name -> Date -> Anniversary Wedding :: Name -> Name -> Date -> Anniversary This is called "GADT syntax" and can be enabled with -XGADTSyntax in GHC.* Cheers Lars * The underlying machinery also extends the fragment of admissible datatype declarations beyond what is possible with the standard syntax. See: https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/data-type-ex...