That is crazy fast... funny, but based on your response I am guessing you don't know why. What could possibly explain such a big difference? Understanding this

That is crazy fast... funny, but based on your response I am guessing you don't know why. What could possibly explain such a big difference? Understanding this is what separates a seasoned pro from someone throwing out trollbait comments about XML and assembly instructions. First off, the resolution of TickCount is not less than 500 milliseconds. Are you sure you are actually timing it right? Maybe you should have used DateTime.Ticks which has a higher resolution. (seriously - I think you need to check your code) But in any case, let's say your test is actually valid. You mentioned "Java line noise" - not really a real explanation for the difference. So let me guess for you - maybe your F# runtime knows the function is pure and idempotent, and after running it once it probably just cached the output. So your run doesn't actually execute the filter across the list for every iteration, whereas my Java code did. I could rewrite my Java code to return the same array over and over after it has been computed once, but it sure won't look as clean as a functional language like F#. I grant you that, and that's one of the reasons I prefer functional languages to Java. Next time maybe put a little more thought into the response if you actually really have no idea why your program said "0.014100 milliseconds".