On Wed, 2007-09-05 at 09:56 +0100, Simon Peyton-Jones wrote:
> Is your suggestion specific to String?
No.
> then I really might have intended to use Complex as a Num type
IME this is much rarer, and I think if a newbie is told that Complex is
not (but needs to be) and instance of Num, it is relatively easy to find
the relevant information (Looking up 'instance' and/or 'class' in the
index of any Haskell text book should do the trick)
> | rephrase to something like "String is not an instance of Num"? For a
> | newbie, it may not be clear that Num is the class and String is the
> | type.
>
> Good point. Not so easy for multi-parameter type classes! E.g. No instance
> for (Bar String Int). So we could have
>
> String is not an instance of class Foo -- single param
> No instance for (Bar String Int) -- multi-param
If you quote things, you can also consider:
'String Int' is not an instance of class 'Bar'.
Downside is that 'String Int' by itself may be confusingly unhaskellish.
-k
_______________________________________________
Haskell-Cafe mailing list
[email protected]
http://www.haskell.org/mailman/listinfo/haskell-cafe
