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 >
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