On 7/13/07, Michael Vanier <[EMAIL PROTECTED]> 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"?
A function f is strict if f _|_ = _|_ -- seq, as defined in Haskell,
is strict in its first argument. So seq does force strict evaluation.
Even if you define "strict evaluation" as evaluating a structure
completely or returning _|_, then you can certainly force strict
evaluation in Haskell -- but you can't write a polymorphic function
that does so, unless you use type class overloading.
Cheers,
Tim
--
Tim Chevalier* catamorphism.org *Often in error, never in doubt
"'There are no atheists in foxholes' isn't an argument against
atheism, it's an argument against foxholes." -- James Morrow
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