It is for the very annoying reason that in order for Error to be a monad it has to implement the "fail" method, which means it has to know how to turn an arbitrary string into a value of your error type. Cheers, Greg On 07/27/10 15:32, Gerald Gutierrez wrote:
Reading the Control.Monad.Error documentation, I see that the Error class has noMsg and strMsg as its only two functions.
Now, I understand that you can define your own Error instances such as in example 1 of the documentation, so why the need to always support strings via noMsg/strMsg ? What uses these? And if in my code, I will never throw an error with a string, am I supposed to implement these functions and then ignore them?
_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe