[rheeseyb]

"Nothing is evaluated unless necessary

head (sort ls)

The list will only be sorted enough to find the minimum"

This may be technically true, but is a pretty bad example with much hand waving - what exactly does it mean to be "sorted enough to find the minimum" given that Haskell uses a merge sort implementation internally?

A better example of Haskell's lazy nature (taken from the Learn You A Haskell book) would be:

take 10 (repeat 5) - it's very easy to comprehend taking the first 10 elements of an infinitely long list without needing to compute the entire list.

[Kutta]

Yep, the "sort only to get head" trick only works fully with selection sort, where it reduces complexity from O(n^2) to O(n) (reduces to a simple max/min). But it also confers some advantage in the case of standard merge sort: the last two sorted sublists will not be merged.

Regarding "repeat", I find it pretty much awesome that it is implemented as a circular linked list with a single element, as in:

    repeat x = xs where xs = x : xs

which ensures that it will take up constant space no matter how "far" in it is evaluated.