[Haskell-cafe] Extending the idea of a general Num to other types?
jules at jellybean.co.uk
Wed Sep 5 07:22:18 EDT 2007
Ketil Malde wrote:
>> 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.
String is not an instance of class Foo
String and Int do not form an instance of multi-parameter class Bar
...alternatively, you can put the more mathsy form in brackets after the
simple one, to make the generalisation from the single param to the
multi-param more clear:
String is not an instance of class Foo (No instance for Foo String)
No instance for (Bar String Int)
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