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"yield break" sequences and "stopping"
f#

Given that I have a unbounded sequence and want to create a bounded sequnce how do I stop a sequence comprehension or how do I trea a infinite sequence as a list, for

example:

let Fib = (1,1) |> Seq.unfold (fun (a, b) -> Some (a, (b, (a + b))))

let FibBelow x =

seq {

for i in Fib do

if i < x then

-> i

else (*how do I stop? *)

}

What should it put in the else to stop the "for"?

(in C# one would say "yield break")

I tried using pattern matching but since a seq isn't a list that really didn't fly either :(

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#light

open System.Collections.Generic

let take_while p (ie :> IEnumerable<'a>) =
  seq
    { use e = ie.GetEnumerator()
      while e.MoveNext() && p e.Current do 
        yield e.Current
    }

let Fib = (1,1) |> Seq.unfold (fun (a, b) -> Some (a, (b, (a + b)))) 

let FibBelow n = take_while (fun x -> x < n) Fib ;;

Hope this helps.

By on 4/26/2008 5:50 AM ()

Julien -- sweet!

A nice definition of take_while ~and~ a good demonstration of unfold :)

By on 4/30/2008 5:38 PM ()

Excellent! That's excalty what I need, thank you very much.

By on 4/26/2008 8:26 AM ()

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