On Wed, May 7, 2008 at 5:05 PM, apfelmus <apfelmus@quantentunnel.de> wrote:

Abhay Parvate wrote:

Just for curiocity, is there a practically useful computation that uses
'seq' in an essential manner, i.e. apart from the efficiency reasons?

I don't think so because you can always replace seq with const id .
In fact, doing so will get you "more" results, i.e. a computation that
did not terminate may do so now.

In other words, we have

seq _|_ = _|_
seq x = id for x > _|_

but

(const id) _|_ = id
(const id) x = id for x > _|_

So, (const id) is always more defined (">") than seq .

For more about _|_ and the semantic approximation order, see

http://en.wikibooks.org/wiki/Haskell/Denotational_semantics

Regards,
apfelmus

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