On 9/11/06, apfelmus@quantentunnel.de
* (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" http://research.microsoft.com/%7Esimonpj/Papers/marktoberdorf/
Thanks; I will take a look at it! Mike