Courtesy of @purefunctor

NameOf.purs

module Main where

import Prelude

import Effect (Effect)
import TryPureScript (p, render, text)
import Data.Generic.Rep (class Generic, Constructor, Sum(..), from)
import Data.Reflectable (class Reflectable, reflectType)
import Type.Proxy (Proxy(..))

data T = A Int | B | C

derive instance Generic T _

class NameOf t where
  nameOf :: t -> String
  
instance Reflectable n String => NameOf (Constructor n a) where
  nameOf _ = reflectType (Proxy :: _ n)

instance (NameOf a, NameOf b) => NameOf (Sum a b) where
  nameOf = case _ of
    Inl a -> nameOf a
    Inr b -> nameOf b

main :: Effect Unit
main = render $ p $ text $ nameOf $ from B