Implement TaskSeq.forall and forallAsync

Author: abelbraaksma

src/FSharp.Control.TaskSeq/TaskSeq.fs

@@ -358,6 +358,9 @@ type TaskSeq private () =
     static member except itemsToExclude source = Internal.except itemsToExclude source
     static member exceptOfSeq itemsToExclude source = Internal.exceptOfSeq itemsToExclude source
 
+    static member forall predicate source = Internal.forall (Predicate predicate) source
+    static member forallAsync predicate source = Internal.forall (PredicateAsync predicate) source
+
     static member exists predicate source =
         Internal.tryFind (Predicate predicate) source
         |> Task.map Option.isSome

src/FSharp.Control.TaskSeq/TaskSeq.fsi

@@ -875,6 +875,30 @@ type TaskSeq =
     /// <exception cref="T:ArgumentNullException">Thrown when the input task sequence is null.</exception>
     static member whereAsync: predicate: ('T -> #Task<bool>) -> source: TaskSeq<'T> -> TaskSeq<'T>
 
+    /// <summary>
+    /// Tests if all elements of the sequence satisfy the given predicate. Stops evaluating
+    /// as soon as <paramref name="predicate" /> returns <see cref="false" />.
+    /// If <paramref name="predicate" /> is asynchronous, consider using <see cref="TaskSeq.forallAsync" />.
+    /// </summary>
+    ///
+    /// <param name="predicate">A function to test an element of the input sequence.</param>
+    /// <param name="source">The input task sequence.</param>
+    /// <returns>A task that, after awaiting, holds true if every element of the sequence satisfies the predicate; false otherwise.</returns>
+    /// <exception cref="T:ArgumentNullException">Thrown when the input task sequence is null.</exception>
+    static member forall: predicate: ('T -> bool) -> source: TaskSeq<'T> -> Task<bool>
+
+    /// <summary>
+    /// Tests if all elements of the sequence satisfy the given asynchronous predicate. Stops evaluating
+    /// as soon as <paramref name="predicate" /> returns <see cref="false" />.
+    /// If <paramref name="predicate" /> is synchronous, consider using <see cref="TaskSeq.forall" />.
+    /// </summary>
+    ///
+    /// <param name="predicate">A function to test an element of the input sequence.</param>
+    /// <param name="source">The input task sequence.</param>
+    /// <returns>A task that, after awaiting, holds true if every element of the sequence satisfies the predicate; false otherwise.</returns>
+    /// <exception cref="T:ArgumentNullException">Thrown when the input task sequence is null.</exception>
+    static member forallAsync: predicate: ('T -> #Task<bool>) -> source: TaskSeq<'T> -> Task<bool>
+
     /// <summary>
     /// Returns a task sequence that, when iterated, skips <paramref name="count" /> elements of the underlying
     /// sequence, and then yields the remainder. Raises an exception if there are not <paramref name="count" />

src/FSharp.Control.TaskSeq/TaskSeqInternal.fs

@@ -690,18 +690,54 @@ module internal TaskSeqInternal =
 
         taskSeq {
             match predicate with
-            | Predicate predicate ->
+            | Predicate syncPredicate ->
                 for item in source do
-                    if predicate item then
+                    if syncPredicate item then
                         yield item
 
-            | PredicateAsync predicate ->
+            | PredicateAsync asyncPredicate ->
                 for item in source do
-                    match! predicate item with
+                    match! asyncPredicate item with
                     | true -> yield item
                     | false -> ()
         }
 
+    let forall predicate (source: TaskSeq<_>) =
+        checkNonNull (nameof source) source
+
+        match predicate with
+        | Predicate syncPredicate -> task {
+            use e = source.GetAsyncEnumerator CancellationToken.None
+            let mutable state = true
+            let! cont = e.MoveNextAsync()
+            let mutable hasMore = cont
+
+            while state && hasMore do
+                state <- syncPredicate e.Current
+
+                if state then
+                    let! cont = e.MoveNextAsync()
+                    hasMore <- cont
+
+            return state
+          }
+
+        | PredicateAsync asyncPredicate -> task {
+            use e = source.GetAsyncEnumerator CancellationToken.None
+            let mutable state = true
+            let! cont = e.MoveNextAsync()
+            let mutable hasMore = cont
+
+            while state && hasMore do
+                let! pred = asyncPredicate e.Current
+                state <- pred
+
+                if state then
+                    let! cont = e.MoveNextAsync()
+                    hasMore <- cont
+
+            return state
+          }
 
     let skipOrTake skipOrTake count (source: TaskSeq<_>) =
         checkNonNull (nameof source) source