I thought that the definition of Permute using thread bombs (http://cs.calstatela.edu/~wiki/index.php/Courses/CS_460/Fall_2005/What_programmers_should_know_about_Oz#Using_the_thread_bomb
) was a very cool little illustration of the power of delayed evaluation for implementing constraints without using extra constraint mechanisms. Isn't anyone else tickled by it? Is it a technique that is so standard that it seems like old hat to everyone else? I'm surprised at lack of response--other than Raph's somewhat sour message.
-- Russ
On 10/24/05, Raphael Collet <[EMAIL PROTECTED]> wrote:
Russ Abbott wrote:
> I'd be interested in your thoughts on
> http://cs.calstatela.edu/~wiki/index.php/Courses/CS_460/Fall_2005/What_programmers_should_know_about_Oz#Thread_bombs
> < http://cs.calstatela.edu/~wiki/index.php/Courses/CS_460/Fall_2005/What_programmers_should_know_about_Oz#Thread_bombs> and
> the example that follows it.
>
> It seems like a nice way to use thread-encapsulated suspension to
> implement go/no-go constraints.
This is the basic requirement for the implementation of a constraint: it
must be checked when all its variables are determined.
> The idea is embed a constraint in a thread that will fail and kill
> off the computation if the constraint fails.
>
> Now that I'm beginning to know about ByNeed and value.Failed, should
> this be written differently? This version seems to do the job.
Constraints are usually implemented by "eager" threads, so that they
fail as soon as possible. ByNeed is more appropriate to functional
style programming.
Value.failed is used to "transmit" an exception from one thread to
another. As exception handling is non-declarative, it is rarely used in
logic or constraint programming contexts.
Cheers,
raph
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