[Haskell-cafe] Either as a Monad instance

Lennart Augustsson lennart at augustsson.net
Tue Oct 3 18:17:43 EDT 2006

It all came about because pattern matching failure sometimes cause a  
do expression to be in MonadZero rather than Monad with the old  
This gave rise to confusing error messages, it was claimed.  This was  
the disease.

	-- Lennart

On Oct 3, 2006, at 08:28 , Ross Paterson wrote:

> On Tue, Oct 03, 2006 at 07:52:54AM -0400, Lennart Augustsson wrote:
>> Yes, having fail in the Monad is a horrible wart.
>> And like some other warts in Haskell it was added to cure the symptom
>> rather than the disease. :(
> Switching metaphors, what do you see as the disease in this case?
> (As far as I know, it's there for the translation of pattern match
> failure in do-expressions.)
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