Laws and partial values (was: [Haskell-cafe] mapM_ ->
Monoid.Monad.map)
roconnor at theorem.ca
roconnor at theorem.ca
Fri Jan 23 20:10:38 EST 2009
On Fri, 23 Jan 2009, Derek Elkins wrote:
> mempty `mappend` undefined = undefined (left identity monoid law)
> The above definition doesn't meet this, similarly for the right identity
> monoid law. That only leaves one definition, () `mappend` () = () which
> does indeed satisfy the monoid laws.
>
> So the answer to the question is "Yes." Another example of making
> things as lazy as possible going astray.
I'd like to argue that laws, such as monoid laws, do not apply to partial
values. But I haven't thought my position through yet.
--
Russell O'Connor <http://r6.ca/>
``All talk about `theft,''' the general counsel of the American Graphophone
Company wrote, ``is the merest claptrap, for there exists no property in
ideas musical, literary or artistic, except as defined by statute.''
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