Implement Option.traverseAsync and Option.sequenceAsync and add tests

Author: tw0po1nt

src/FsToolkit.ErrorHandling/Option.fs

@@ -321,6 +321,28 @@ module Option =
 
         opt
 
+    /// Converts a Option<Async<_>> to an Async<Option<_>>
+    let inline sequenceAsync (optAsync: Option<Async<'T>>) : Async<Option<'T>> =
+        async {
+            match optAsync with
+            | Some asnc ->
+                let! x = asnc
+                return Some x
+            | None -> return None
+        }
+
+    /// <summary>
+    /// Maps an Async function over an Option, returning an Async Option.
+    /// </summary>
+    /// <param name="f">The function to map over the Option.</param>
+    /// <param name="opt">The Option to map over.</param>
+    /// <returns>An Async Option with the mapped value.</returns>
+    let inline traverseAsync
+        ([<InlineIfLambda>] f: 'T -> Async<'T>)
+        (opt: Option<'T>)
+        : Async<Option<'T>> =
+        sequenceAsync ((map f) opt)
+
     /// <summary>
     /// Creates an option from a boolean value and a value of type 'a.
     /// If the boolean value is true, returns <c>Some</c> value.

tests/FsToolkit.ErrorHandling.Tests/Option.fs

@@ -184,6 +184,66 @@ let teeIfTests =
             Expect.equal foo "foo" ""
     ]
 
+let sequenceAsyncTests =
+    testList "Option.sequenceAsync Tests" [
+        testCaseAsync "sequenceAsync returns the async value if Some"
+        <| async {
+            let optAsync =
+                async { return "foo" }
+                |> Some
+
+            let! value =
+                optAsync
+                |> Option.sequenceAsync
+
+            Expect.equal value (Some "foo") ""
+        }
+
+        testCaseAsync "sequenceAsync returns None if None"
+        <| async {
+            let optAsync = None
+
+            let! value =
+                optAsync
+                |> Option.sequenceAsync
+
+            Expect.equal value None ""
+        }
+    ]
+
+let traverseAsyncTests =
+    testList "Option.traverseAsync Tests" [
+        testCaseAsync "traverseAsync returns the async value if Some"
+        <| async {
+            let optAsync = Some "foo"
+
+            let optFunc =
+                id
+                >> Async.singleton
+
+            let! value =
+                (optFunc, optAsync)
+                ||> Option.traverseAsync
+
+            Expect.equal value (Some "foo") ""
+        }
+
+        testCaseAsync "traverseAsync returns None if None"
+        <| async {
+            let optAsync = None
+
+            let optFunc =
+                id
+                >> Async.singleton
+
+            let! value =
+                (optFunc, optAsync)
+                ||> Option.traverseAsync
+
+            Expect.equal value None ""
+        }
+    ]
+
 let traverseResultTests =
     testList "Option.traverseResult Tests" [
         testCase "traverseResult with Some of valid data"
@@ -366,6 +426,8 @@ let optionOperatorsTests =
 
 let allTests =
     testList "Option Tests" [
+        sequenceAsyncTests
+        traverseAsyncTests
         traverseResultTests
         tryParseTests
         tryGetValueTests