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