On Wed, Oct 19, 2011 at 5:03 PM, Johan Tibell <johan.tibell@gmail.com> wrote:
>
> It does. You need to use evaluate to have ensure actually be evaluated.
>

I'm almost certain you're wrong about this. The bang pattern on the
return from ensure (!r1 <- ensure $ ...) forces r1 to WHNF, which goes
through deepseq, and thus the whole list is forced. See
https://gist.github.com/1299380 for a short counterexample.

I should have paid more attention; I missed the bangs on the bindings.

I still recommend the pattern I linked in my previous email. If you want to do it they way you currently do use

let !foo = xs `deepseq` xs

no return needed.