Ketil,
 
Thanks for the response. It seems that defining them as a pair only postphones the error.
GHC will give an error when you extract the components of the pair, no matter whether you add
the "NoMonomorphismRestriction" flag or not.
 
--{-# LANGUAGE NoMonomorphismRestriction #-}
p :: (Show a, Ord b) => (a -> String, b -> b -> Bool)
p = (id . show, flip (<))
f1 = fst p
f2 = snd p
-----------------------
Without NoMonomorphismRestriction, I got:

D:\work\test1.hs:6:10:
    Ambiguous type variable `a0' in the constraint:
      (Show a0) arising from a use of `p'
    Possible cause: the monomorphism restriction applied to the following:
      f1 :: a0 -> String (bound at D:\work\hsOcaml\test1.hs:6:1)
    Probable fix: give these definition(s) an explicit type signature
                  or use -XNoMonomorphismRestriction
    In the first argument of `fst', namely `p'
    In the expression: fst p
    In an equation for `f1': f1 = fst p
D:\work\hsOcaml\test1.hs:6:10:
    Ambiguous type variable `b0' in the constraint:
      (Ord b0) arising from a use of `p'
    Probable fix: add a type signature that fixes these type variable(s)
...... 
Failed, modules loaded: none.
 
------------------
With NoMonomorphismRestriction, I got:
 

D:\work\test1.hs:6:10:
    Ambiguous type variable `b0' in the constraint:
      (Ord b0) arising from a use of `p'
    Probable fix: add a type signature that fixes these type variable(s)
    In the first argument of `fst', namely `p'
    In the expression: fst p
    In an equation for `f1': f1 = fst p
D:\work\test1.hs:7:10:
    Ambiguous type variable `a0' in the constraint:
      (Show a0) arising from a use of `p'
    Probable fix: add a type signature that fixes these type variable(s)
    In the first argument of `snd', namely `p'
    In the expression: snd p
    In an equation for `f2': f2 = snd p
Failed, modules loaded: none.
 
 
Thanks,

 Ting