Change monad to myMonad in haskell

I wrote a function that evaluates an expression.

import Data.Sequence as S (Seq(..), fromList)
import Data.Either (partitionEithers)

data HiFun =  HiFunList
  deriving (Show,Eq, Ord)  

data HiValue = HiValueNumber Rational
  | HiValueList (Seq HiValue)
  deriving (Show, Eq, Ord)

data HiExpr = HiExprValue HiValue
  | HiExprApply HiExpr [HiExpr]
  deriving Show

data HiError = HiErrorInvalidArgument
  | HiErrorInvalidFunction
  | HiErrorArityMismatch
  deriving Show

--eval :: Monad m => HiExpr -> m (Either HiError HiValue)
eval :: HiMonad m => HiExpr -> m (Either HiError HiValue) 
eval (HiExprValue a ) = return (Right a)
eval (HiExprApply (HiExprValue (HiValueNumber  _) ) _ ) = return (Left HiErrorInvalidFunction)
eval (HiExprApply exp args ) =  do
  op <- eval exp
  case op of 
    (Right (HiValueFunction HiFunList)) -> do 
      ll <- return (fmap (\x -> do a <- eval x ; a ) args) -- args :: [HiExpr]
      return (toL ll)


toL :: [(Either HiError HiValue)] -> (Either HiError HiValue)
toL xs  = let (ls, rs) = partitionEithers xs in
  if (length ls == 0)
  then (Right (HiValueList (fromList rs) ))
  else (Left HiErrorInvalidArgument)

I had to add

class Monad m => HiMonad m where
  runAction :: HiAction -> m HiValue

and change

eval :: Monad m => HiExpr -> m (Either HiError HiValue)

to

eval :: HiMonad m => HiExpr -> m (Either HiError HiValue)

And I got error

 • Could not deduce (HiMonad (Either HiError))
        arising from a use of ‘eval’
      from the context: HiMonad m
        bound by the type signature for:
                   eval :: forall (m :: * -> *).
                           HiMonad m =>
                           HiExpr -> m (Either HiError HiValue)
        at src\HW3\Evaluator.hs:19:1-57
    • In a stmt of a 'do' block: a <- eval x
      In the expression:
        do a <- eval x
           a
      In the first argument of ‘fmap’, namely
        ‘(\ x
            -> do a <- eval x
                  a)’
   |
28 |       ll <- return (fmap (\x -> do a <- eval x ; a ) args)
   |                                         ^^^^^^

As I could understand we don't have

instance HiMonad (Either HiError)

I think instance HiMonad (Either HiError) couldn't be written because of Monad m => HiMonad m Extra Text, Extra Text. Extra Text. Extra Text, Extra Text.

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