Bugs item #648903, was opened at 2002-12-05 10:44
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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'
----------------------------------------------------------------------
>Comment By: Simon Marlow (simonmar)
Date: 2002-12-05 10:54
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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