Typeclass instance head is invalid

Main.purs

module Main where

import Debug.Trace
import Control.Monad.RWS
import Control.Monad.RWS.Class
import Control.Monad.RWS.Trans
import Control.Monad.Identity
import Data.Monoid
import Data.Tuple

main = do
  trace "Yo!"
  trace $ showSee $ runRWS calc 42 10

-- Doesn't work:
-- Warning: Error at src/Main.purs line 19, column 1:
-- Error in type (log :: w, result :: a, state :: s):
-- Type class instance head is invalid. Use --force to continue.
instance showSee :: (Show s, Show a, Show w) => Show { state :: s, result :: a, log :: w} where
  show see = "See { " ++
    "state: " ++ (show see.state) ++
    " result: " ++ (show see.result) ++
    " log: " ++ (show see.log) ++ "}"

-- Works
showSee :: forall s a w. (Show s, Show a, Show w) => { state :: s, result :: a, log :: w } -> String
showSee see = "See { " ++
  "state: " ++ (show see.state) ++
  " result: " ++ (show see.result) ++
  " log: " ++ (show see.log) ++ "}"


calc :: RWS Number [String] Number Number
calc = do
  x <- get
  tell ["Starting with value from state:" ++ (show x)]
  y <- ask
  tell ["Adding the value from the read:" ++ (show y)]
  let result = x + y
  tell $ ["Ending up with " ++ show result]
  put result
  return result

I ran into a similar issue. Did you figure out what the issue was?