FSharp.Core

11.0.100 - Unlisted on NuGet

Fixed

Mirror compiler-semantic attributes (e.g. [<NoDynamicInvocation>], [<Experimental>]) in .fsi signature files to match .fs implementations. (Issue #19560, PR #19880)
Fix Array2D AOT compatibility: create, init and rebase no longer emit IL3050; map, mapi and copy no longer emit it on net10.0; the *Based operations now warn at the call site before the runtime failure they already had. (Language Suggestion #1454, PR #20338)
Fix Array.exists2 documentation examples to use equal-length arrays; the previous examples would throw ArgumentException at runtime instead of returning the documented false/true values. (PR #19672)
Move Async.StartChild to the "Starting Async Computations" docs category alongside Async.StartChildAsTask. (Issue #19667)
Add InlineIfLambda to Array.init (PR #19869)
Fix printf handling of -0.0 (negative zero) values for float, float32, and decimal values (Issue #15557 and Issue #15558, PR #18147)

Added

Add Unchecked.withNull, an interop escape hatch that re-types any 'T to 'T | null without the usual not null/not struct constraints, so unconstrained C# nullable-generic APIs (e.g. T? M<T>()) can be implemented and consumed from F#. (Issue #17734, PR #20232)
Added generic print and printn functions ('T -> unit) to ExtraTopLevelOperators for simple value printing to stdout. (RFC FS-1125, PR #19265)
Ship FSharp.Core with an additional net10.0 target framework (next to netstandard2.0 and netstandard2.1). The net-TFM assembly is public-surface-identical to the netstandard2.1 one; the target version is a pinned, deliberately advanced knob. (PR #20229)
Add Async.Await, mirroring Async.AwaitTask semantics, but elides egregious AggregateException wrapping. Includes ValueTask support, and a SRTP-based overload accepting any Task-like value that supports the GetAwaiter protocol. (Language Suggestion #840, PR #19785)
Async.RunSynchronouslyImmediate: runs work on the calling thread until the first asynchronous suspension (as opposed to RunSynchronously, which immediately offloads if not on a background and/or threadpool thread). (Issue #1042, PR #19804)
Added AllowOverloadOnReturnTypeAttribute: applying it to a method causes its return type to be considered during overload resolution, enabling overloads that differ only by return type. (fslang-suggestions#820, PR #19602)
Added modules for Async, Task and ValueTask with consistent result, map, bind, ignore, catchWith, catch, and empty functions (LanguageSuggestion #1466, PR #19844)
Added conversion functions Task.ofValueTask and ValueTask.ofTask. (LanguageSuggestion #1466, PR #19844)
Add Async.StartTaskImmediate: passes the ambient Async.CancellationToken to a task factory, then await the result using Async.Await semantics. Overloads for Task, Task<'T>, ValueTask, ValueTask<'T> and task-like .GetAwaiter() (via SRTP). (Language Suggestion #1284, PR #20258)
Add Async.RunSynchronouslyImmediate: runs work on the calling thread until the first asynchronous suspension (as opposed to RunSynchronously, which immediately offloads if not on a background and/or threadpool thread). (Issue #1042, PR #19804)
Add modules for Async, Task and ValueTask with consistent result, map, bind, ignore, catchWith, catch, and empty functions (LanguageSuggestion #1466, PR #19844)
Add conversion functions Task.ofValueTask and ValueTask.ofTask. (LanguageSuggestion #1466, PR #19844)
Add parallelLimit to Task and Async modules, for bounded-parallelism execution of async/task computations, flowing cancellation and returning the results as an array. (LanguageSuggestion #1467, PR #20294)
Add parallelDoLimit to Task and Async modules, for bounded-parallelism execution of async/task computations, flowing cancellation. (LanguageSuggestion #1467, PR #20294)
Add sequentialDo to Task and Async, running computations one at a time, flowing cancellation, without yielding an egregious unit[]. (LanguageSuggestion #1467, PR #20294)
Add Task.sequential, running task computations one at a time, flowing cancellation and returning the results as an array. (LanguageSuggestion #1467, PR #20294)
Add Task.startAsyncImmediate, starting an Async<'T> on the current thread and returning a Task<'T>, flowing cancellation. (LanguageSuggestion #1467, PR #20294)

Changed

Deduplicate repeated XML documentation (sort stability/complexity, Parallel.For, dynamic entry points) via the compile-time <include> tag; generated FSharp.Core.xml is unchanged. (PR #20231)
Remove trailing whitespace from source files. No functional change: whitespace inside string literals and inactive #if regions is preserved. (PR #20355)

10.1.300 - 2026-05-12

Fixed

Optimize Set.intersect performance symmetry and preserve identity from the first set argument. (PR #19291) (Fixes #19139)
Fix anonymous record field ordering in LINQ expression conversion to produce consistent expression trees regardless of field declaration order. (Issue #11131, Issue #15648)
Fix array indexing in LINQ expressions to generate proper array index expressions instead of GetArray method calls, enabling LINQ providers like Azure Cosmos DB to translate array access. (Issue #16918)
Fix tuple join conditions and groupBy operations to properly compare tuple keys using structural equality. AnonymousObject types now implement Equals and GetHashCode, enabling inline tuple joins like join b on ((a.Id1, a.Id2) = (b.Id1, b.Id2)) to work correctly. (Issue #7885, Issue #47)
Fix tuple/multi-value projections in queries to use Queryable.Select instead of Enumerable.Select when the source is IQueryable, preserving query composition and enabling async operations like ToListAsync() in Entity Framework Core. (Issue #3782, Issue #15133)
Fix EvaluateQuotation to handle Sequential expressions, void method calls (unit return), and other patterns that were previously throwing NotSupportedException. Also properly handles unit-returning expressions by using Action delegates instead of Func delegates. (Issue #19099)
Fix query conditionals without else branch (if-then only) that were causing type mismatch errors. Now properly extracts element type from IQueryable for creating empty sequences. (Issue #3445)
Fix Seq.empty rendering as "EmptyEnumerable" in serializers by delegating to System.Linq.Enumerable.Empty<'T>() instead of using a custom DU type. (Issue #17864, PR #19317)
Fix seq { try/with } handler body executing twice when source throws immediately and handler yields nothing. (Issue #19660, PR #19661)
Ensure culture-independent parsing of .NET-style interpolated string holes. (Issue #19367, PR #19370)

Added

Add List.partitionWith, Array.partitionWith, Set.partitionWith, and Array.Parallel.partitionWith functions that partition a collection using a function that returns Choice<'T1, 'T2>. (Language Suggestion #1119)

Changed

Added complexity documentation (Big-O notation) to all 462 functions across Array, List, Seq, Map, and Set collection modules. (PR #19240)

10.1.201 - 2026-03-12

Fixed

Fix IL2091 trimming warning in LazyExtensions.Create by adding DynamicallyAccessedMembers attribute to the generic type parameter. (Issue #17356, PR #18302)

Changed

Added not null constraints to IDelegateEvent<'Delegate>, IEvent<'Delegate,'Args>, DelegateEvent<'Delegate>, and Event<'Delegate,'Args> types to prevent spurious nullness warnings when implementing CLIEvent properties. (Issue #18361, Issue #18349, PR #19221)
Renamed deprecated or and & operators, but keeping the original compiled names for binary compatibility. (PR #19143)

10.0.100 - 2025-11-11

Fixed

Correct a typo in docs for List.sort (PR #18938)

Added

Enable more string optimizations by adding when 'T : Enum library-only library-only static optimization constraint. (PR #18546)

Changed

Random functions support for zero element chosen/sampled (PR #18568)
Optimize array slicing performance. (PR #18778)

Breaking Changes

1D array slicing now returns an empty array singleton instead of allocating a new array when the result is empty. (PR #18778)

9.0.300 - 2025-05-13

Fixed

Modified the behavior of Array.insertManyAt to return a copy of the original array when inserting an empty array. (PR #18353)

Added

Added nullability annotations to .Using builder method for async and task builders (PR #18292)
Support for and! in TaskBuilder (LanguageSuggestion #1363, PR #18451)

Breaking Changes

Struct unions with overlapping fields now generate mappings needed for reading via reflection (Issue #18121, PR #18274). Previous versions of FSharp.Core returned incomplete mapping between fields and cases, these older fslib versions will now report an exception.

9.0.201 - 2025-02-11

Fixed

Fix exception on Post after MailboxProcessor was disposed (Issue #17849, PR #17922)
Fix missing null annotation in Async.SwitchToContext (Issue #18055, PR #18059)

Changed

String function changed to guarantee a non-null string return type (PR #17809)
Add Parameters as valid target for the Struct attribute (Language suggestion #1136, PR #18098)

FSharp.Core 9.0.101 did not change compared to version 9.0.100. Below are the changes for FSharp.Core 9.0.100

Fixed

Struct UnionCase doesn't seem to be a valid target for the DefaultAugmentationAttribute (Issue #17499, PR #17502)

Added

Enable C# collection expression support for F# lists & sets. (Language suggestion #1355, RFC FS-1145 (PR#776), PR #17359)
Add module functions for converting between 'T option and 'T voption. (PR #17436)

Changed

Change compiler default setting realsig+ when building assemblies (Issue #17384, PR #17378)
Change compiler default setting for compressedMetadata (Issue #17379, PR #17383)
Enable FSharp 9.0 Language Version (Issue #17497), PR))
Struct UnionCase doesn't seem to be a valid target for the DefaultAugmentationAttribute (Issue #17499, PR #17502)

9.0.100 - 2024-11-12

Fixed

Struct UnionCase doesn't seem to be a valid target for the DefaultAugmentationAttribute (Issue #17499, PR #17502)

Added

Enable C# collection expression support for F# lists & sets. (Language suggestion #1355, RFC FS-1145 (PR#776), PR #17359)
Add module functions for converting between 'T option and 'T voption. (PR #17436)

Changed

Change compiler default setting realsig+ when building assemblies (Issue #17384, PR #17378)
Change compiler default setting for compressedMetadata (Issue #17379, PR #17383)
Enable FSharp 9.0 Language Version (Issue #17497), PR))
Struct UnionCase doesn't seem to be a valid target for the DefaultAugmentationAttribute (Issue #17499, PR #17502)

8.0.400 - 2024-08-13

Added

Random functions for collections (RFC #1135, PR #17277)

Changed

Cache delegate in query extensions. (PR #17130)
Update AllowNullLiteralAttribute to also use AttributeTargets.Interface (PR #17173)
Update StructAttribute to also use AttributeTargets.Class (PR #17207)

Breaking Changes

Fixed argument exception throwing inconsistency - accessing an out-of-bounds collection index will now throw ArgumentOutOfRangeException instead of ArgumentException (#17328)

8.0.300 - 2024-05-14

Added

Minor tweaks to inline specifications to support Visibility PR (PR #15484, #PR 16427
Optimize equality in generic contexts. (PR #16615)
Add a constructor for MailboxProcessor with a flag denoting that an exception will be thrown when Post is called after the MailboxProcessor has been disposed. (PR #13036)

Fixed

Preserve original stack traces in resumable state machines generated code if available. (PR #16568)
Fix receiving and processing mailbox after Dispose. (PR #13036)
Enforce AttributeTargets on structs and classes. Also update RequireQualifiedAccessAttribute and AutoOpenAttribute to use AttributeTargets.Struct (PR #16790)
Enforce AttributeTargets on enums. Also update RequireQualifiedAccessAttribute to use AttributeTargets.Enum (PR #16887)
Enforce AttributeTargets on delegates. Also update ReflectedDefinitionAttribute to use AttributeTargets.Delegate (PR #16891)

8.0.200 - 2024-02-13

Added

More inlines for Result module. (PR #16106)
Added a new parameterless constructor for CustomOperationAttribute (PR #16475, part of implementation for fslang-suggestions/1250)

namespace System

namespace System.IO

namespace Markdig

module Common

val path: string

type Path = static member ChangeExtension: path: string * extension: string -> string static member Combine: path1: string * path2: string -> string + 4 overloads static member EndsInDirectorySeparator: path: ReadOnlySpan<char> -> bool + 1 overload static member Exists: path: string -> bool static member GetDirectoryName: path: ReadOnlySpan<char> -> ReadOnlySpan<char> + 1 overload static member GetExtension: path: ReadOnlySpan<char> -> ReadOnlySpan<char> + 1 overload static member GetFileName: path: ReadOnlySpan<char> -> ReadOnlySpan<char> + 1 overload static member GetFileNameWithoutExtension: path: ReadOnlySpan<char> -> ReadOnlySpan<char> + 1 overload static member GetFullPath: path: string -> string + 1 overload static member GetInvalidFileNameChars: unit -> char array ...
<summary>Performs operations on <see cref="T:System.String" /> instances that contain file or directory path information. These operations are performed in a cross-platform manner.</summary>

Path.Combine(paths: System.ReadOnlySpan<string>) : string
Path.Combine( paths: string array) : string
Path.Combine(path1: string, path2: string) : string
Path.Combine(path1: string, path2: string, path3: string) : string
Path.Combine(path1: string, path2: string, path3: string, path4: string) : string

val renderPackageReleaseNotes: packageName: string -> path: string -> minPackageVersion: System.Version -> packageVersionOfNotes: (System.Version -> System.Version) -> upcomingVersion: System.Version -> string
Renders the release notes of a package: one section per notes file in `path`, ordered by
package version, newest first. Which package versions belong to a notes file is looked up
from the source commit of each package on NuGet, from `minPackageVersion` on.

Notes without a package are either the upcoming release, placed at the top as `upcomingVersion`,
or an old servicing version that never shipped, placed where `packageVersionOfNotes` puts it.

Multiple items
type Version = interface ICloneable interface IComparable interface IComparable<Version> interface IEquatable<Version> interface IFormattable interface ISpanFormattable interface IUtf8SpanFormattable interface IUtf8SpanParsable<Version> new: unit -> unit + 4 overloads member Clone: unit -> obj ...
<summary>Represents the version number of an assembly, operating system, or the common language runtime. This class cannot be inherited.</summary>

--------------------
System.Version() : System.Version
System.Version(version: string) : System.Version
System.Version(major: int, minor: int) : System.Version
System.Version(major: int, minor: int, build: int) : System.Version
System.Version(major: int, minor: int, build: int, revision: int) : System.Version

val id: x: 'T -> 'T

val upcomingFSharpVersion: System.Version
The F# version main is at, and the FCS version that goes with it