AsyncSeq.unfoldAsync

Author: eulerfx

src/FSharpx.Async/AssemblyInfo.fs

@@ -4,9 +4,9 @@ open System.Reflection
 [<assembly: AssemblyTitleAttribute("FSharpx.Async")>]
 [<assembly: AssemblyProductAttribute("FSharpx.Async")>]
 [<assembly: AssemblyDescriptionAttribute("Async extensions for F#")>]
-[<assembly: AssemblyVersionAttribute("1.9.8")>]
-[<assembly: AssemblyFileVersionAttribute("1.9.8")>]
+[<assembly: AssemblyVersionAttribute("1.9.9")>]
+[<assembly: AssemblyFileVersionAttribute("1.9.9")>]
 do ()
 
 module internal AssemblyVersionInformation =
-    let [<Literal>] Version = "1.9.8"
+    let [<Literal>] Version = "1.9.9"

src/FSharpx.Async/AsyncSeq.fs

@@ -487,6 +487,14 @@ module AsyncSeq =
   let toList (input:AsyncSeq<'T>) : Async<'T list> =
     input |> fold (fun arr a -> a::arr) []
 
+  /// Generates an async sequence using the specified generator function.
+  let rec unfoldAsync (f:'State -> Async<('T * 'State) option>) (s:'State) : AsyncSeq<'T> = asyncSeq {        
+    let! r = f s
+    match r with
+    | Some (a,s) -> 
+      yield a
+      yield! unfoldAsync f s
+    | None -> () }
 
 [<AutoOpen>]
 module AsyncSeqExtensions = 

tests/FSharpx.Async.Tests/AsyncSeqTests.fs

@@ -28,6 +28,7 @@ let ``toArray should collect the results into an array``() =
 
   Assert.True(([1;2;3] = a))
 
+
 [<Test>]
 let ``toList should collect the results into an array``() =
 
@@ -41,5 +42,19 @@ let ``toList should collect the results into an array``() =
 
   Assert.True(([1;2;3] = a))
 
-    
+
+[<Test>]
+let ``unfoldAsync should generate a sequence``() =
+  
+  let gen s = 
+    if s < 3 then (s,s + 1) |> Some |> async.Return
+    else None |> async.Return
+  
+  let s = 
+    AsyncSeq.unfoldAsync gen 0 
+    |> AsyncSeq.toList 
+    |> Async.RunSynchronously
+
+  Assert.True(([0;1;2] = s))
+