NHC98 and GHC 4.08.1 differ on monad related functions

[Jos� Romildo Malaquias]

Hello.

While porting Haskore to NHC98 I got an error
I am not understanding. I have attached a test
module that shows the error message:

$ nhc98 -c Test.hs

====================================
        Error after type deriving/checking:
No default for  Monad.MonadPlus at 7:1.(171,[(2,209)])
No default for  Monad.MonadPlus at 6:1.(174,[(2,208)])

GHC 4.08.1 and Hugs98 accepts the code without
complaining.

Any hints?

Romildo
-- 
Prof. Jos� Romildo Malaquias <[EMAIL PROTECTED]>
Departamento de Computa��o
Universidade Federal de Ouro Preto
Brasil

module Test where

import Monad

zeroOrMore, oneOrMore :: MonadPlus m => m a -> m [a]
zeroOrMore m      = return [] `mplus` oneOrMore m
oneOrMore  m      = do { a <- m; as <- zeroOrMore m; return (a:as) }