Implement TaskSeq.init, initAsync, initInfinite, initInfiniteAsync an…

…d TaskSeq.concat, plus tests and docs

src/FSharpy.TaskSeq.Test/FSharpy.TaskSeq.Test.fsproj

@@ -15,6 +15,7 @@
     <Compile Include="TaskSeq.Cast.Tests.fs" />
     <Compile Include="TaskSeq.Choose.Tests.fs" />
     <Compile Include="TaskSeq.Collect.Tests.fs" />
+    <Compile Include="TaskSeq.Concat.Tests.fs" />
     <Compile Include="TaskSeq.Empty.Tests.fs" />
     <Compile Include="TaskSeq.ExactlyOne.Tests.fs" />
     <Compile Include="TaskSeq.Filter.Tests.fs" />
@@ -23,6 +24,7 @@
     <Compile Include="TaskSeq.Fold.Tests.fs" />
     <Compile Include="TaskSeq.Head.Tests.fs" />
     <Compile Include="TaskSeq.Indexed.Tests.fs" />
+    <Compile Include="TaskSeq.Init.Tests.fs" />
     <Compile Include="TaskSeq.IsEmpty.fs" />
     <Compile Include="TaskSeq.Item.Tests.fs" />
     <Compile Include="TaskSeq.Iter.Tests.fs" />

src/FSharpy.TaskSeq.Test/TaskSeq.Concat.Tests.fs

@@ -0,0 +1,51 @@
+module FSharpy.Tests.Concat
+
+open System
+
+open Xunit
+open FsUnit.Xunit
+open FsToolkit.ErrorHandling
+
+open FSharpy
+open System.Collections.Generic
+
+//
+// TaskSeq.concat
+//
+
+let validateSequence ts =
+    ts
+    |> TaskSeq.toSeqCachedAsync
+    |> Task.map (Seq.map string)
+    |> Task.map (String.concat "")
+    |> Task.map (should equal "123456789101234567891012345678910")
+
+module EmptySeq =
+    [<Theory; ClassData(typeof<TestEmptyVariants>)>]
+    let ``TaskSeq-concat with empty sequences`` variant =
+        taskSeq {
+            yield Gen.getEmptyVariant variant // not yield-bang!
+            yield Gen.getEmptyVariant variant
+            yield Gen.getEmptyVariant variant
+        }
+        |> TaskSeq.concat
+        |> verifyEmpty
+
+    [<Theory; ClassData(typeof<TestEmptyVariants>)>]
+    let ``TaskSeq-concat with top sequence empty`` variant =
+        Gen.getEmptyVariant variant
+        |> TaskSeq.box
+        |> TaskSeq.cast<IAsyncEnumerable<int>> // casting an int to an enumerable, LOL!
+        |> TaskSeq.concat
+        |> verifyEmpty
+
+module Immutable =
+    [<Theory; ClassData(typeof<TestImmTaskSeq>)>]
+    let ``TaskSeq-concat with empty sequences`` variant =
+        taskSeq {
+            yield Gen.getSeqImmutable variant // not yield-bang!
+            yield Gen.getSeqImmutable variant
+            yield Gen.getSeqImmutable variant
+        }
+        |> TaskSeq.concat
+        |> validateSequence

src/FSharpy.TaskSeq.Test/TaskSeq.Init.Tests.fs

@@ -0,0 +1,142 @@
+module FSharpy.Tests.Init
+
+open System
+
+open Xunit
+open FsUnit.Xunit
+open FsToolkit.ErrorHandling
+
+open FSharpy
+
+//
+// TaskSeq.init
+// TaskSeq.initInfinite
+// TaskSeq.initAsync
+// TaskSeq.initInfiniteAsync
+//
+
+/// Asserts that a sequence contains the char values 'A'..'J'.
+
+module EmptySeq =
+    [<Fact>]
+    let ``TaskSeq-init can generate an empty sequence`` () = TaskSeq.init 0 (fun x -> x) |> verifyEmpty
+
+    [<Fact>]
+    let ``TaskSeq-initAsync can generate an empty sequence`` () =
+        TaskSeq.initAsync 0 (fun x -> Task.fromResult x)
+        |> verifyEmpty
+
+    [<Fact>]
+    let ``TaskSeq-init with a negative count gives an error`` () =
+        fun () ->
+            TaskSeq.init -1 (fun x -> Task.fromResult x)
+            |> TaskSeq.toArrayAsync
+            |> Task.ignore
+
+        |> should throwAsyncExact typeof<ArgumentException>
+
+        fun () ->
+            TaskSeq.init Int32.MinValue (fun x -> Task.fromResult x)
+            |> TaskSeq.toArrayAsync
+            |> Task.ignore
+
+        |> should throwAsyncExact typeof<ArgumentException>
+
+    [<Fact>]
+    let ``TaskSeq-initAsync with a negative count gives an error`` () =
+        fun () ->
+            TaskSeq.initAsync Int32.MinValue (fun x -> Task.fromResult x)
+            |> TaskSeq.toArrayAsync
+            |> Task.ignore
+
+        |> should throwAsyncExact typeof<ArgumentException>
+
+module Immutable =
+    [<Fact>]
+    let ``TaskSeq-init singleton`` () =
+        TaskSeq.init 1 id
+        |> TaskSeq.head
+        |> Task.map (should equal 0)
+
+    [<Fact>]
+    let ``TaskSeq-initAsync singleton`` () =
+        TaskSeq.initAsync 1 (id >> Task.fromResult)
+        |> TaskSeq.head
+        |> Task.map (should equal 0)
+
+    [<Fact>]
+    let ``TaskSeq-init some values`` () =
+        TaskSeq.init 42 (fun x -> x / 2)
+        |> TaskSeq.length
+        |> Task.map (should equal 42)
+
+    [<Fact>]
+    let ``TaskSeq-initAsync some values`` () =
+        TaskSeq.init 42 (fun x -> Task.fromResult (x / 2))
+        |> TaskSeq.length
+        |> Task.map (should equal 42)
+
+    [<Fact>]
+    let ``TaskSeq-initInfinite`` () =
+        TaskSeq.initInfinite (fun x -> x / 2)
+        |> TaskSeq.item 1_000_001
+        |> Task.map (should equal 500_000)
+
+    [<Fact>]
+    let ``TaskSeq-initInfiniteAsync`` () =
+        TaskSeq.initInfiniteAsync (fun x -> Task.fromResult (x / 2))
+        |> TaskSeq.item 1_000_001
+        |> Task.map (should equal 500_000)
+
+module SideEffects =
+    let inc (i: int byref) =
+        i <- i + 1
+        i
+
+    [<Fact>]
+    let ``TaskSeq-init singleton with side effects`` () = task {
+        let mutable x = 0
+
+        let ts = TaskSeq.init 1 (fun _ -> inc &x)
+
+        do! TaskSeq.head ts |> Task.map (should equal 1)
+        do! TaskSeq.head ts |> Task.map (should equal 2)
+        do! TaskSeq.head ts |> Task.map (should equal 3) // state mutates
+    }
+
+    [<Fact>]
+    let ``TaskSeq-init singleton with side effects -- Current`` () = task {
+        let mutable x = 0
+
+        let ts = TaskSeq.init 1 (fun _ -> inc &x)
+
+        let enumerator = ts.GetAsyncEnumerator()
+        let! _ = enumerator.MoveNextAsync()
+        do enumerator.Current |> should equal 1
+        do enumerator.Current |> should equal 1
+        do enumerator.Current |> should equal 1 // current state does not mutate
+    }
+
+    [<Fact>]
+    let ``TaskSeq-initAsync singleton with side effects`` () = task {
+        let mutable x = 0
+
+        let ts = TaskSeq.initAsync 1 (fun _ -> Task.fromResult (inc &x))
+
+        do! TaskSeq.head ts |> Task.map (should equal 1)
+        do! TaskSeq.head ts |> Task.map (should equal 2)
+        do! TaskSeq.head ts |> Task.map (should equal 3) // state mutates
+    }
+
+    [<Fact>]
+    let ``TaskSeq-initAsync singleton with side effects -- Current`` () = task {
+        let mutable x = 0
+
+        let ts = TaskSeq.initAsync 1 (fun _ -> Task.fromResult (inc &x))
+
+        let enumerator = ts.GetAsyncEnumerator()
+        let! _ = enumerator.MoveNextAsync()
+        do enumerator.Current |> should equal 1
+        do enumerator.Current |> should equal 1
+        do enumerator.Current |> should equal 1 // current state does not mutate
+    }

src/FSharpy.TaskSeq/TaskSeq.fs

@@ -156,8 +156,18 @@ module TaskSeq =
     //
 
     let length source = Internal.lengthBy None source
+    let lengthOrMax max source = Internal.lengthBeforeMax max source
     let lengthBy predicate source = Internal.lengthBy (Some(Predicate predicate)) source
     let lengthByAsync predicate source = Internal.lengthBy (Some(PredicateAsync predicate)) source
+    let init count initializer = Internal.init (Some count) (InitAction initializer)
+    let initInfinite initializer = Internal.init None (InitAction initializer)
+    let initAsync count initializer = Internal.init (Some count) (InitActionAsync initializer)
+    let initInfiniteAsync initializer = Internal.init None (InitActionAsync initializer)
+
+    let concat (sources: taskSeq<#taskSeq<'T>>) = taskSeq {
+        for ts in sources do
+            yield! (ts :> taskSeq<'T>)
+    }
 
     //
     // iter/map/collect functions
@@ -262,6 +272,7 @@ module TaskSeq =
         | None -> return Internal.raiseNotFound ()
     }
 
+
     let findAsync predicate source = task {
         match! Internal.tryFind (PredicateAsync predicate) source with
         | Some item -> return item

src/FSharpy.TaskSeq/TaskSeq.fsi

@@ -15,10 +15,17 @@ module TaskSeq =
 
     /// <summary>
     /// Returns the length of the sequence. This operation requires the whole sequence to be evaluated and
-    /// should not be used on potentially infinite sequences.
+    /// should not be used on potentially infinite sequences, see <see cref="lengthOrMax" /> for an alternative.
     /// </summary>
     val length: source: taskSeq<'T> -> Task<int>
 
+    /// <summary>
+    /// Returns the length of the sequence, or <paramref name="max" />, whichever comes first. This operation requires the task sequence
+    /// to be evaluated in full, or until <paramref name="max" /> items have been processed. Use this method instead of
+    /// <see cref="TaskSeq.length" /> if you want to prevent too many items to be evaluated, or if the sequence is potentially infinite.
+    /// </summary>
+    val lengthOrMax: max: int -> source: taskSeq<'T> -> Task<int>
+
     /// <summary>
     /// Returns the length of the sequence of all items for which the <paramref name="predicate" /> returns true.
     /// This operation requires the whole sequence to be evaluated and should not be used on potentially infinite sequences.
@@ -32,6 +39,74 @@ module TaskSeq =
     /// </summary>
     val lengthByAsync: predicate: ('T -> #Task<bool>) -> source: taskSeq<'T> -> Task<int>
 
+    /// <summary>
+    /// Generates a new task sequence which, when iterated, will return successive elements by calling the given function
+    /// with the current index, up to the given count. Each element is saved after its initialization for successive access to
+    /// <see cref="IAsyncEnumerator.Current" />, which will not re-evaluate the <paramref name="initializer" />. However,
+    /// re-iterating the returned task sequence will re-evaluate the initialization function. The returned sequence may
+    /// be passed between threads safely. However, individual IEnumerator values generated from the returned sequence should
+    /// not be accessed concurrently.
+    /// </summary>
+    ///
+    /// <param name="count">The maximum number of items to generate for the sequence.</param>
+    /// <param name="initializer">A function that generates an item in the sequence from a given index.</param>
+    /// <returns>The resulting task sequence.</returns>
+    /// <exception cref="T:System.ArgumentException">Thrown when count is negative.</exception>
+    val init: count: int -> initializer: (int -> 'T) -> taskSeq<'T>
+
+    /// <summary>
+    /// Generates a new task sequence which, when iterated, will return successive elements by calling the given function
+    /// with the current index, up to the given count. Each element is saved after its initialization for successive access to
+    /// <see cref="IAsyncEnumerator.Current" />, which will not re-evaluate the <paramref name="initializer" />. However,
+    /// re-iterating the returned task sequence will re-evaluate the initialization function. The returned sequence may
+    /// be passed between threads safely. However, individual IEnumerator values generated from the returned sequence should
+    /// not be accessed concurrently.
+    /// </summary>
+    ///
+    /// <param name="count">The maximum number of items to generate for the sequence.</param>
+    /// <param name="initializer">A function that generates an item in the sequence from a given index.</param>
+    /// <returns>The resulting task sequence.</returns>
+    /// <exception cref="T:System.ArgumentException">Thrown when count is negative.</exception>
+    val initAsync: count: int -> initializer: (int -> #Task<'T>) -> taskSeq<'T>
+
+    /// <summary>
+    /// Generates a new task sequence which, when iterated, will return successive elements by calling the given function
+    /// with the current index, ad infinitum, or until <see cref="Int32.MaxValue" /> is reached.
+    /// Each element is saved after its initialization for successive access to
+    /// <see cref="IAsyncEnumerator.Current" />, which will not re-evaluate the <paramref name="initializer" />. However,
+    /// re-iterating the returned task sequence will re-evaluate the initialization function. The returned sequence may
+    /// be passed between threads safely. However, individual IEnumerator values generated from the returned sequence should
+    /// not be accessed concurrently.
+    /// </summary>
+    ///
+    /// <param name="initializer">A function that generates an item in the sequence from a given index.</param>
+    /// <returns>The resulting task sequence.</returns>
+    val initInfinite: initializer: (int -> 'T) -> taskSeq<'T>
+
+    /// <summary>
+    /// Generates a new task sequence which, when iterated, will return successive elements by calling the given function
+    /// with the current index, ad infinitum, or until <see cref="Int32.MaxValue" /> is reached.
+    /// Each element is saved after its initialization for successive access to
+    /// <see cref="IAsyncEnumerator.Current" />, which will not re-evaluate the <paramref name="initializer" />. However,
+    /// re-iterating the returned task sequence will re-evaluate the initialization function. The returned sequence may
+    /// be passed between threads safely. However, individual IEnumerator values generated from the returned sequence should
+    /// not be accessed concurrently.
+    /// </summary>
+    ///
+    /// <param name="initializer">A function that generates an item in the sequence from a given index.</param>
+    /// <returns>The resulting task sequence.</returns>
+    val initInfiniteAsync: initializer: (int -> #Task<'T>) -> taskSeq<'T>
+
+    /// <summary>
+    /// Combines the given task sequence of task sequences and concatenates them end-to-end, to form a
+    /// new flattened, single task sequence. Each task sequence is awaited item by item, before the next is iterated.
+    /// </summary>
+    ///
+    /// <param name="sources">The input enumeration-of-enumerations.</param>
+    /// <returns>The resulting task sequence.</returns>
+    /// <exception cref="T:ArgumentNullException">Thrown when the input sequence is null.</exception>
+    val concat: sources: taskSeq<#taskSeq<'T>> -> taskSeq<'T>
+
     /// Returns taskSeq as an array. This function is blocking until the sequence is exhausted and will properly dispose of the resources.
     val toList: source: taskSeq<'T> -> 'T list