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haskellreflectionghcgeneric-programmingderiving

Haskell: Get data constructor name as string

Let us say we have

data D = X Int | Y Int Int | Z String

I wish to have a function getDConst

getDConst :: D -> String

that returns either "X", "Y", or "Z", according to the data constructor used for its input. Is there a generic way to write this without having to do case on every data constructor? (I am ok with solutions relying on Data.Typeable or something similar)

Solution

  • Found the solution myself, but leaving this question to help others:

    import Data.Data
data D = X Int | Y Int Int deriving (Data,Typeable)

let result = show $ toConstr (X 3) -- result contains what we wanted