title: LINQ queries on possibly infinite lists
body: <p>I am currently doing some Project Euler problems and the earlier ones often involve things like Fibonacci numbers or primes. Iterating over them seems to be a natural fit for LINQ, at least in readability and perceived "elegance" of the code (I'm trying to use language-specific features where possible and applicable to get a feel for the languages).</p>
  
  <p>My problem is now, if I only need a set of numbers up to a certain limit, how should I best express this? Currently I have hard-coded the respective limit in the iterator but I'd really like the enumerator to return the list until something outside decides not to query it anymore, since it's over a certain limit. So basically that I have a potentially infinite iterator but I only take a finite set of numbers from it. I know such things are trivial in functional languages, but I wonder whether C# allows for that, too. The only other idea I had would be to have an iterator Primes(long) that returns primes up to a certain limit, likewise for other sequences.</p>
  
  <p>Any ideas?</p>