C#

__John_ wrote:

It uses a 'lazy' strategy, ie. only evaluating an expression or executing a function when the result is actually needed, am I right?

List<Person> peoples = new List<Person> {new Person("wayne"), new Person("sarah"), new Person("mark"), new Person("simon"), new Person("ashleigh"), new Person("dave"), new Person("connor"), new Person("bronwyn"), new Person("chantelle"), new Person("will"), new Person("chris")};

int Count = people.Count(p => p.Name.StartsWith("w")); //<-- Count is a greedy operator and all persons are evaluated for a result of 2.

var firstperson = people.Where(p => p.Name.Length == 5).Take(3);
foreach (var p in firstperson) // <-- evaluation start where and only Wayne, Sarah, Mark and Simon will be evaluated. The rest of the list is left alone
{
   Console.WriteLine(p.Name);
}

// And to show you when Linq expression are evaluated, try 
var firstperson2 = people.Where(p => p.Name.Length == 5).Take(3);
people.Insert(1, new Person("Vince"));

foreach (var p in firstperson) // <-- evaluation start where and only Wayne, Vince ans Sarah, will be evaluated. The rest of the list is left alone
{
    Console.WriteLine(p.Name);
}

__John_ wrote:

BTW: How can I enumerate the results more that once?