Lazy minimum

[David Menendez]

On Wed, Nov 19, 2008 at 8:06 PM, Dave Bayer <bayer at cpw.math.columbia.edu> wrote:

> What I'm wondering, however, is if there is a way to code "minimum"
> efficiently in general,
>
>> minimum :: Ord a => [a] -> a
>
>
> where one knows absolutely nothing further about the type "a", but one
> believes that lazy evaluation will run afoul of the above issue.
>
> It would seem that this would require compiler support, allowing code to
> access approximations to lazy data generalizing the head of a lazy list. I'm
> reminded of working with power series by working mod x^n for various n.
> Here, I'd like a bounded version of "compare", that returned EQ for data
> that agreed to a specified lazy evaluation depth.
>
> Did I miss that class? Is there a construct in GHC that would allow me to
> write "minimum" efficiently for lazy data?

One possibility would be to add minimum and maximum to Ord with the
appropriate default definitions, similar to Monoid's mconcat.

-- 
Dave Menendez <dave at zednenem.com>
<http://www.eyrie.org/~zednenem/>