[Haskell-cafe] Re: evaluate vs seq
viritrilbia at gmail.com
Tue Sep 12 13:20:02 EDT 2006
On 9/11/06, apfelmus at quantentunnel.de <apfelmus at quantentunnel.de> wrote:
> > * (a `seq` return a) = evaluate a *right now*, then produce an IO action
> > which, when executed, returns the result of evaluating a. Thus, if
> > a is undefined, throws an exception right now.
> is a bit misleading as there is no evaluation "right now". It's better
> to say that (a `seq` return a) is _|_ ("bottom", i.e. undefined) when a
> == _|_.
Sure... but what about when a is not _|_? I would also like to
understand the difference between `seq' and `evaluate' for arguments
that are defined. How would you describe that without talking about
"when" expressions are evaluated?
> For a more detailed semantics of exceptions in Haskell, see
> " Tackling the awkward squad: monadic input/output, concurrency,
> exceptions, and foreign-language calls in Haskell"
Thanks; I will take a look at it!
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