extract field names from rows using rowtolist

extract-fieldnames.purs

module Main where

import Prelude

import Control.Monad.Eff (Eff)
import Control.Monad.Eff.Console (CONSOLE, logShow)
import Data.Symbol (class IsSymbol, SProxy(..), reflectSymbol)
import Type.Proxy (Proxy(..))
import Type.Row (class ListToRow, class RowToList, Cons, Nil, kind RowList)

class RollMySausage (rowList :: RowList) where
  rollMySausage :: forall row
    . RowToList row rowList
    => Proxy (Record row)
    -> Array String

instance rmsCons ::
  ( IsSymbol name
  , RollMySausage tail
  , ListToRow tail tailRow
  , RowToList tailRow tail
  ) => RollMySausage (Cons name ty tail) where
  rollMySausage _ = [name] <> rest
    where
      name = reflectSymbol (SProxy :: SProxy name)
      rest = rollMySausage (Proxy :: Proxy (Record tailRow))

instance rmsNil :: RollMySausage Nil where
  rollMySausage _ = []

type MyTest =
  { a :: Int
  , b :: String
  , c :: Boolean
  }

main :: forall e. Eff (console :: CONSOLE | e) Unit
main = do
  logShow $ rollMySausage (Proxy :: Proxy MyTest)
  -- outputs ["a","b","c"]