Control.Monad.Writer.Strict not as strict as expected

Henning Thielemann lemming at
Thu Sep 15 23:12:00 CEST 2011

On Thu, 15 Sep 2011, Edward Kmett wrote:

> The Strict/Lazy writer split has nothing to do with the strictness of your monoid, but
> rather whether or not operations such as:
> > fmap f ~(w, a) = (w, f a)

Doesn't this violate the fmap law

   fmap id = id


   fmap id undefined = (undefined, undefined)


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