On Fri, 2007-07-13 at 17:20 -0700, Michael Vanier wrote:
Stefan,
Thanks for your comments, as always.
What I meant by really-truly-absolutely-I-mean-right-now-seq is something that would evaluate its argument as far as it is possible to do so i.e. something that forces strict evaluation of an argument. That's what I thought seq did, but now I see I was wrong; it only "goes one deep" as it were. In fact, as you say, seq is not defined in terms of evaluation; all that it guarantees is that its first argument is either (a) bottom, in which the result of the entire seq is bottom, or (b) not bottom. To do so it has to evaluate the first argument only far enough to show bottom-ness or not, which is not strict evaluation as I understand it. So am I right in saying that Haskell has no way to force strict evaluation? Or am I confused as to the correct definition of "strict"?
There's no polymorphic reduce to normal form function, though one could be implemented as a primitive. There are two typeclasses for this, the DeepSeq library that floats around and NFData in Control.Parallel.Strategies (with method rnf, wonder where they got that...) This is not unreasonable. seq being polymorphic is a significant source of woe (it was not always so).