Signature context in recursive groups

Hello,

I have a problem with signature contexts in mutually
recursive groups. I want to write a scanner, which is
able to read inputs of the form "int(3)" or
"float(2,0)" and return corresponding values of the
datatype:

data Token = TInt Int
	   | TFloat Float
   deriving (Read,Show)

Both constructors have the same type. Therefore, I want
to pass them to another function, which reads the
corresponding number with the function reads:

scan :: String -> [Token]
scan ('i':'n':'t':str) = scanNumber TInt str
scan ('f':'l':'o':'a':'t':str) = scanNumber TInt str

scanNumber :: Read a => (a -> Token) -> String ->
[Token]
scanNumber tokenCons ('(':str) = case reads str of
		                   ((n,(')':str1)):_) -> tokenCons
                                                                           
n:scan str1
		                   _            -> error "no literal"

main = print (scan "int(4)")

In Hugs this program works fine, but ghc does not
accept it, because of a mutually recursive group. Is
this a feature or a bug?
What does the Haskell 98 standard say?

Thanks and regards,

Frank Huch

Trac metadata

Trac field	Value
Version	5.0
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	ResolvedWon'tFix
Component	Compiler (Type checker)
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