Merge pull request #382 from fsprojects/repo-assist/perf-while-bang-cleanup-20260409-5ddbcb4cb509276b

[Repo Assist] perf: use while! in iter/fold/reduce/mapFold/tryLast/Drop/Truncate

Author: dsyme

AGENTS.md

@@ -10,7 +10,7 @@ FSharp.Control.TaskSeq is an F# library providing a `taskSeq` computation expres
 - `src/FSharp.Control.TaskSeq.Test/` — xUnit test project (net10.0)
 - `src/FSharp.Control.TaskSeq.SmokeTests/` — Smoke/integration tests
 - `src/FSharp.Control.TaskSeq.sln` — Solution file
-- `Version.props` — Single source of truth for the package version
+- `Version.props` — Package version (derived automatically from `release-notes.txt`)
 - `build.cmd` — Windows build/test script used by CI
 
 ## Build
@@ -102,12 +102,28 @@ All workflows are in `.github/workflows/`:
 
 ## Release Notes
 
-**Required**: Every PR that adds features, fixes bugs, or makes user-visible changes **must** include an update to `release-notes.txt`. Add a bullet under the appropriate version heading (currently `0.5.0`). The format is:
+`release-notes.txt` is the **single source of truth** for the package version. `Version.props` extracts the version automatically by finding the first line that matches a `X.Y.Z` semver pattern. The `Unreleased` section at the top of the file is skipped because it does not match this pattern.
+
+**Format requirements:**
+
+- The file **must** always begin with a heading line `Unreleased` (after the optional `Release notes:` header). This section holds in-progress changes before they are assigned a version number. It must always be present, even if empty.
+- Below `Unreleased`, versioned sections are listed in descending order (`1.0.0`, `0.7.0`, …). The topmost versioned section determines the package version.
+- To bump the version, add a new version heading between `Unreleased` and the previous version.
+
+Example:
 
 ```
-0.5.0
+Release notes:
+
+Unreleased
+    - upcoming change description
+
+1.1.0
     - adds TaskSeq.myFunction and TaskSeq.myFunctionAsync, #<issue>
     - fixes <description>, #<issue>
+
+1.0.0
+    - adds TaskSeq.withCancellation, #167
 ```
 
-If you are bumping to a new version, also update `Version.props`. PRs that touch library source (`src/FSharp.Control.TaskSeq/`) without updating `release-notes.txt` are incomplete.
+**Required**: Every PR that adds features, fixes bugs, or makes user-visible changes **must** add a bullet under the `Unreleased` heading in `release-notes.txt`. PRs that touch library source (`src/FSharp.Control.TaskSeq/`) without updating `release-notes.txt` are incomplete.

Version.props

@@ -1,6 +1,6 @@
 <Project>
   <PropertyGroup>
-    <!-- updating this version will trigger a publish after merge to 'main' -->
-    <Version>1.0.0</Version>
+    <!-- Version is extracted from the first versioned section heading in release-notes.txt -->
+    <Version>$([System.Text.RegularExpressions.Regex]::Match($([System.IO.File]::ReadAllText(`$(MSBuildThisFileDirectory)release-notes.txt`)), `(?m)^(\d+\.\d+\.\d+)`).Groups.get_Item(1).Value)</Version>
   </PropertyGroup>
-</Project>
+</Project>

release-notes.txt

@@ -1,20 +1,24 @@
 
 Release notes:
 
+Unreleased
+
+1.1.1
+    - perf: use while! in groupBy, countBy, partition, except, exceptOfSeq to eliminate redundant mutable 'go' variables and initial MoveNextAsync calls
+
 1.1.0
     - adds TaskSeq.chooseV, TaskSeq.chooseVAsync, #385
 
 1.0.0
-    - perf: use while! in groupBy, countBy, partition, except, exceptOfSeq to eliminate redundant mutable 'go' variables and initial MoveNextAsync calls
     - adds taskSeqDynamic computation expression and TaskSeqDynamic/TaskSeqDynamicInfo types for dynamic (FSI-compatible) resumable code, fixing issue where taskSeq would raise NotImplementedException in F# Interactive, #246
+    - perf: simplify iter, fold, reduce, mapFold, tryLast, skipOrTake (Drop/Truncate) to use while! and remove manual go-flag and initial MoveNextAsync pre-advance, matching the pattern already used by sum/sumBy/average
     - perf: toResizeArrayAsync (and therefore toArrayAsync, toListAsync, toResizeArrayAsync, toIListAsync) uses a direct loop instead of going through iter, avoiding a lambda and DU allocation per call
     - perf: tryItem uses a simpler loop that skips the redundant inner index check on every iteration
     - perf: TaskSeq.chunkBy and chunkByAsync reuse the ResizeArray buffer between chunks, reducing allocations on sequences with many chunk boundaries
     - fixes: TaskSeq.insertAt, insertManyAt, removeAt, removeManyAt, updateAt now raise ArgumentNullException (not NullReferenceException) when given a null source; insertManyAt also validates the values argument
     - refactor: simplify lengthBy and lengthBeforeMax to use while! and remove the redundant mutable 'go' and initial MoveNextAsync
     - refactor: simplify tryTail inner loop to use while!, removing redundant mutable 'go' flag and initial MoveNextAsync
     - adds TaskSeq.distinctUntilChangedWith and TaskSeq.distinctUntilChangedWithAsync, #345
-    - adds TaskSeq.withCancellation, #167
     - adds TaskSeq.replicateInfinite, replicateInfiniteAsync, replicateUntilNoneAsync, #345
     - adds TaskSeq.firstOrDefault, lastOrDefault, #345
     - adds TaskSeq.splitAt, #345
@@ -25,6 +29,9 @@ Release notes:
     - docs: adds missing XML <returns> documentation tags to singleton, isEmpty, length, lengthOrMax, lengthBy, and lengthByAsync
     - test: adds 70 new tests to TaskSeq.Fold.Tests.fs covering call-count assertions, folder-not-called-on-empty, ordering, null initial state, and fold/foldAsync equivalence
 
+1.0.0
+    - adds TaskSeq.withCancellation, #167
+
 0.7.0
     - performance: TaskSeq.exists, existsAsync, contains no longer allocate an intermediate Option value
     - test: adds 67 tests for TaskSeq.lengthOrMax (previously untested)

src/FSharp.Control.TaskSeq/TaskSeqInternal.fs

@@ -362,68 +362,49 @@ module internal TaskSeqInternal =
 
         task {
             use e = source.GetAsyncEnumerator CancellationToken.None
-            let mutable go = true
-            let! step = e.MoveNextAsync()
-            go <- step
 
-            // this ensures that the inner loop is optimized for the closure
-            // though perhaps we need to split into individual functions after all to use
-            // InlineIfLambda?
+            // Each branch keeps its own while! loop so the match dispatch is hoisted out and
+            // the JIT sees a tight, single-case loop (same pattern as sum/sumBy etc.).
             match action with
             | CountableAction action ->
                 let mutable i = 0
 
-                while go do
-                    do action i e.Current
-                    let! step = e.MoveNextAsync()
+                while! e.MoveNextAsync() do
+                    action i e.Current
                     i <- i + 1
-                    go <- step
 
             | SimpleAction action ->
-                while go do
-                    do action e.Current
-                    let! step = e.MoveNextAsync()
-                    go <- step
+                while! e.MoveNextAsync() do
+                    action e.Current
 
             | AsyncCountableAction action ->
                 let mutable i = 0
 
-                while go do
+                while! e.MoveNextAsync() do
                     do! action i e.Current
-                    let! step = e.MoveNextAsync()
                     i <- i + 1
-                    go <- step
 
             | AsyncSimpleAction action ->
-                while go do
+                while! e.MoveNextAsync() do
                     do! action e.Current
-                    let! step = e.MoveNextAsync()
-                    go <- step
         }
 
     let fold folder initial (source: TaskSeq<_>) =
         checkNonNull (nameof source) source
 
         task {
             use e = source.GetAsyncEnumerator CancellationToken.None
-            let mutable go = true
             let mutable result = initial
-            let! step = e.MoveNextAsync()
-            go <- step
 
             match folder with
             | FolderAction folder ->
-                while go do
+                while! e.MoveNextAsync() do
                     result <- folder result e.Current
-                    let! step = e.MoveNextAsync()
-                    go <- step
 
             | AsyncFolderAction folder ->
-                while go do
+                while! e.MoveNextAsync() do
                     let! tempResult = folder result e.Current
                     result <- tempResult
-                    let! step = e.MoveNextAsync()
-                    go <- step
 
             return result
         }
@@ -462,22 +443,16 @@ module internal TaskSeqInternal =
                 raiseEmptySeq ()
 
             let mutable result = e.Current
-            let! step = e.MoveNextAsync()
-            let mutable go = step
 
             match folder with
             | FolderAction folder ->
-                while go do
+                while! e.MoveNextAsync() do
                     result <- folder result e.Current
-                    let! step = e.MoveNextAsync()
-                    go <- step
 
             | AsyncFolderAction folder ->
-                while go do
+                while! e.MoveNextAsync() do
                     let! tempResult = folder result e.Current
                     result <- tempResult
-                    let! step = e.MoveNextAsync()
-                    go <- step
 
             return result
         }
@@ -487,28 +462,21 @@ module internal TaskSeqInternal =
 
         task {
             use e = source.GetAsyncEnumerator CancellationToken.None
-            let mutable go = true
             let mutable state = initial
             let results = ResizeArray()
-            let! step = e.MoveNextAsync()
-            go <- step
 
             match folder with
             | MapFolderAction folder ->
-                while go do
+                while! e.MoveNextAsync() do
                     let result, newState = folder state e.Current
                     results.Add result
                     state <- newState
-                    let! step = e.MoveNextAsync()
-                    go <- step
 
             | AsyncMapFolderAction folder ->
-                while go do
+                while! e.MoveNextAsync() do
                     let! (result, newState) = folder state e.Current
                     results.Add result
                     state <- newState
-                    let! step = e.MoveNextAsync()
-                    go <- step
 
             return results.ToArray(), state
         }
@@ -813,15 +781,10 @@ module internal TaskSeqInternal =
 
         task {
             use e = source.GetAsyncEnumerator CancellationToken.None
-            let mutable go = true
             let mutable last = ValueNone
-            let! step = e.MoveNextAsync()
-            go <- step
 
-            while go do
+            while! e.MoveNextAsync() do
                 last <- ValueSome e.Current
-                let! step = e.MoveNextAsync()
-                go <- step
 
             match last with
             | ValueSome value -> return Some value
@@ -1255,24 +1218,19 @@ module internal TaskSeqInternal =
             else
                 taskSeq {
                     use e = source.GetAsyncEnumerator CancellationToken.None
+                    let mutable i = 0
+                    let mutable cont = true
 
-                    let! step = e.MoveNextAsync()
-                    let mutable cont = step
-                    let mutable pos = 0
-
-                    // skip, or stop looping if we reached the end
-                    while cont do
-                        pos <- pos + 1
-
-                        if pos < count then
-                            let! moveNext = e.MoveNextAsync()
-                            cont <- moveNext
-                        else
-                            cont <- false
+                    // advance past 'count' elements; stop early if the source is shorter
+                    while cont && i < count do
+                        let! hasMore = e.MoveNextAsync()
+                        if hasMore then i <- i + 1 else cont <- false
 
-                    // return the rest
-                    while! e.MoveNextAsync() do
-                        yield e.Current
+                    // return remaining elements; enumerator is at element (count-1) so one
+                    // more MoveNext is needed to reach element (count)
+                    if cont then
+                        while! e.MoveNextAsync() do
+                            yield e.Current
 
                 }
         | Take ->
@@ -1299,19 +1257,16 @@ module internal TaskSeqInternal =
             else
                 taskSeq {
                     use e = source.GetAsyncEnumerator CancellationToken.None
+                    let mutable yielded = 0
+                    let mutable cont = true
 
-                    let! step = e.MoveNextAsync()
-                    let mutable cont = step
-                    let mutable pos = 0
-
-                    // return items until we've exhausted the seq
-                    while cont do
-                        yield e.Current
-                        pos <- pos + 1
+                    // yield up to 'count' elements; stop when exhausted or limit reached
+                    while cont && yielded < count do
+                        let! hasMore = e.MoveNextAsync()
 
-                        if pos < count then
-                            let! moveNext = e.MoveNextAsync()
-                            cont <- moveNext
+                        if hasMore then
+                            yield e.Current
+                            yielded <- yielded + 1
                         else
                             cont <- false