Side Effects and Functional Programming

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re: Side Effects and Functional Programming

podwysocki — Wed, 17 Sep 2008 00:30:15 GMT

@Logicalmind

Yes, to move the scope of the reader within the function itself would definitely be an answer to the problem. To contain the IO action is probably the best bet, or avoid laziness altogether.

Matt

re: Side Effects and Functional Programming

Logicalmind — Tue, 16 Sep 2008 19:44:27 GMT

C# Version of Resource Management:

Func<string> ReadLines = () =>

{

using (var fs = File.OpenText("abc.txt"))

{

return fs.ReadToEnd();

}

};

Console.WriteLine(ReadLines());

re: Side Effects and Functional Programming

podwysocki — Sun, 14 Sep 2008 17:36:27 GMT

@Laurent

I agree that there are places such as dealing with resources or exception handling sometimes doesn't make a good match. Unfortunately, the languages here I used aren't pure in a way that I can declare what happens inside of them, and then be able to react accordingly. Maybe in the future, we could have some static analysis or some other mechanism to help with that.

Sure, a sequence computation expression could help and I think that's the ideal situation there. But for exception management, there is no real good answer using lazy evaluation I think.

Matt

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re: Side Effects and Functional Programming

Laurent — Sat, 13 Sep 2008 10:43:23 GMT

Hi,

There are some good examples here. Sometimes, we just don't want lazy evaluation. For example, in your Exception Management problem, it seems that it's a bad idea to use lazy evaluation (we want to know if all elements are valid before returning any value - thus, we want strict evaluation).

If you want side effects to occur at most once, you should use Seq.cache.

For Resource Management, I suggest:

let readLines = seq {

use reader = System.IO.File.OpenText(@"D:\Foo.txt")

yield reader.ReadToEnd() }