On 11/6/07, Graham Fawcett <[EMAIL PROTECTED]> wrote:
> ToString.hs:5:0:
> Illegal instance declaration for `MyShow String'
> (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 `MyShow String'
>
> ToString.hs:6:0:
> Illegal instance declaration for `MyShow a'
> (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 `MyShow a'
In ghc 6.8.1, the error messages are more helpful:
foo.hs:5:0:
Illegal instance declaration for `MyShow String'
(All instance types must be of the form (T t1 ... tn)
where T is not a synonym.
Use -XTypeSynonymInstances if you want to disable this.)
In the instance declaration for `MyShow String'
foo.hs:6:0:
Illegal instance declaration for `MyShow a'
(All instance types must be of the form (T a1 ... an)
where a1 ... an are distinct type *variables*
Use -XFlexibleInstances if you want to disable this.)
In the instance declaration for `MyShow a'
When I run with -XTypeSynonymInstances -XFlexibleInstances it works.
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