On Mon, May 26, 2014 at 5:21 PM, Daniel Fischer <daniel.is.fischer@googlemail.com> wrote:

To evaluate something completely, one needs to evaluate a value that depends
on the complete structure. Presumably, to determine the length of the list,
one needs to evaluate all paths completely to see whether they lead to a valid
puzzle, hence the evaluation is forced by demanding the evaluation of the
length.

To avoid that presumption, you could also write

evaluate $ rnf x

whenever x is an instance of NFData.

The length function strikes me as a kludgy stand-in for rnf when rnf is really what's meant.

-- Kim-Ee