Fixes Result while loops

Author: TheAngryByrd

src/FsToolkit.ErrorHandling/ResultCE.fs

@@ -74,19 +74,16 @@ module ResultCE =
                 [<InlineIfLambda>] guard: unit -> bool,
                 [<InlineIfLambda>] generator: unit -> Result<unit, 'error>
             ) : Result<unit, 'error> =
-            if guard () then
-                let mutable whileBuilder = Unchecked.defaultof<_>
-
-                whileBuilder <-
-                    fun () ->
-                        this.Bind(
-                            this.Run generator,
-                            (fun () -> if guard () then this.Run whileBuilder else this.Zero())
-                        )
-
-                this.Run whileBuilder
-            else
-                this.Zero()
+
+            let rec whileBuilder =
+                fun () ->
+                    if guard () then
+                        this.Bind(this.Run(fun () -> generator ()), (fun () -> this.Run(fun () -> whileBuilder ())))
+                    else
+                        this.Zero()
+
+            this.Run(fun () -> whileBuilder ())
+
 
         member inline this.For
             (

tests/FsToolkit.ErrorHandling.Tests/ResultCE.fs

@@ -236,15 +236,30 @@ let ``ResultCE loop Tests`` =
         testCase "while"
         <| fun () ->
             let data = 42
-            let mutable index = 0
+            let maxLoop = 10
+            let mutable index = maxLoop
 
             let actual = result {
                 while index < 10 do
                     index <- index + 1
 
                 return data
             }
+            Expect.equal index maxLoop "index should match maxLoop"
+            Expect.equal actual (Result.Ok data) "Should be ok"
+        testCase "while long"
+        <| fun () ->
+            let data = 42
+            let mutable index = 0
+            let maxLoop = 1000000
+            let actual = result {
+                while index < maxLoop do
+                    index <- index + 1
+
+                return data
+            }
 
+            Expect.equal index (maxLoop ) "index should match maxLoop"
             Expect.equal actual (Result.Ok data) "Should be ok"
         testCase "for in"
         <| fun () ->