[ ghc-Bugs-648903 ] can't declare instance for type synonim

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Bugs item #648903, was opened at 2002-12-05 02:44
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Category: Compiler (Type checker)
Group: None
Status: Closed
Resolution: Rejected
Priority: 5
Submitted By: Igor (alar)
Assigned to: Nobody/Anonymous (nobody)
Summary: can't declare instance for type synonim

Initial Comment:
Trying to load into GHCi simple program (in attached 
file) I receive error stating I can declare class instances 
only for types defined using "data". I beleive it is a bug 
because Hugs handles this situation normally.
Error message:
/igor/tst.hs:1:
    No instance for `Eq (Stack -> Stack)'
    When deriving the `Eq' instance for type `Object'

/igor/tst.hs:1:
    No instance for `Show (Stack -> Stack)'
    When deriving the `Show' instance for type `Object'

/igor/tst.hs:4:
    Illegal instance declaration for `Eq Operator'
        (The instance type must be of form (T a b c)
         where T is not a synonym, and a,b,c are distinct 
type variables)
    In the instance declaration for `Eq Operator'

/igor/tst.hs:6:
    Illegal instance declaration for `Show Operator'
        (The instance type must be of form (T a b c)
         where T is not a synonym, and a,b,c are distinct 
type variables)
    In the instance declaration for `Show Operator'


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>Comment By: Sigbjorn Finne (sigbjorn)
Date: 2002-12-05 09:04

Message:
Logged In: YES 
user_id=232905

To get at the 'wrong' behaviour with GHC(i), use -fglasgow-
exts.

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Comment By: Simon Marlow (simonmar)
Date: 2002-12-05 02:54

Message:
Logged In: YES 
user_id=48280

Hugs is wrong on this one, the H98 report states that an 
instance type cannot refer to a type synonym (section 4.3.2).

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