With this release, we are enabling F# support for multi-targeting with VS2010. This means that VS2010 projects can be targeted to produce binaries for any of .NET 2.0-4.0, for example if you are a library vendor building 2.0 dlls for use on 2.0-4.0, or working in an environment where .NET 2.0-3.5 development is the norm. Additionally, we will be supporting development of F# components targeting Silverlight, through the inclusion of a template for Silverlight library components. In line with the philosophy we outlined in the previous release of F#, we expect the focus of F# in this domain to be components that handle the algorithmic and communication patterns common in client-side programming, particularly in enterprise scenarios.



We have also taken crucial steps towards our goal of ensuring binary compatibility for components across .NET 2.0-4.0. For example, in previous releases different copies of the F# Power Pack were required for .NET 2.0-3.5 and 4.0. However, in this release we have one version of the Power Pack which can be used on both .NET 2.0-4.0 (installed via the CTP MSI or ZIP). If you are authoring F# binary components, you can now build binary compatible components in a similar way (note: some important Beta2 caveats are in the release notes). As we have discussed with the F# community, full ongoing binary compatibility is expected starting with the version of F# that comes with the Visual Studio 2010 RTM release.



At the source level, we are now aiming for no more changes to FSharp.Core.dll before the Visual Studio 2010 RTM release, apart from removing deprecated functionality. Existing F# users should pay careful attention to deprecation warnings since we will be removing deprecated functionality with the version of F# that will come with the Visual Studio 2010 RTM release.



There are also some simplifications to the F# language. For example, the OverloadID attribute is no longer needed when defining method overloads, we have added support for placing definitions in the global namespace and simplified conversion operators such as int32. Some important restrictions have been lifted with regard to object oriented programming, and discriminated unions now have a cleaner code generation pattern when used from other .NET languages. We’ve also made F# programming safer by adding a new feature called equality and comparison constraints used to ensure that F# types such as Map and Set are only used with types supporting the necessary operations. This is documented further in the F# release notes, and an update to the F# language specification will follow in the next week.



This release also includes final, relatively modest improvements to the F# Core Library. These include simplifications to F# asynchronous programming. For example, using asynchronous programming with WPF, Silverlight and ASP.NET components is now even easier, as described in the release notes. We have included the array2D operator for creating 2D arrays. We’ve also addressed version-stable serialization of Map and Set, and aligned F# lazy values and cancellation with the designs of .NET 4.0. F# first class events now support the IObservable interface (new in .NET 4.0, also supported by F# 2.0, and also used by the Reactive Framework). The F# library also includes a modest library of Observable operators, following the pattern of the Event operators already present in F#.



F# now supports reusable script components through the support of #load on .fsx components. By taking the closure of script references, common code can now by factored into reusable .fsx components. These components can be executed with F# Interactive, or compiled with the command line F# compiler.



For F# in Visual Studio, we have addressed a multitude of issues, including F1 support, improvements for the Error List, issues in the Project System and better debugger display of unions and other F# types. For F# documentation, the F# Core Library docs have been integrated into MSDN.

# Release

* F# in Visual Studio2010 Beta2 can build applications for .NET 2.0/3.0/3.5/4.0 and Silverlight 2/3.
* Updated F# CTP for Visual Studio 2008
* F# PowerPack available as part of the CTP Update, and can be used with either CTP Update of VS2010 Beta2

# F# Language

* OverloadID no longer required for defining overridden methods
* Require module/namespace at top of files
* ‘comparison’ and ‘equality’ constraints
* Core conversion operators use .NET standard op_Implicit/op_Explicit instead or ToInt32, etc.
* Support for global namespace qualification, “global.A.B.C” and “namespace global”
* More flexibility in defining yield! and return! in computation expressions using YieldFrom and ReturnFrom
* Extension methods can participate in overload resolution
* Support for volatile fields using [<Volatile>]
* Support for letting F# types allow “null” using [<AllowNullLiteral>]
* Interface implementations can now be inherited
* Private type abbreviations (type private X = int)
* More flexibility for list literals and subtyping
* Recursive type inference improvement

# F# Compiler

* HTML doc generation moved from compiler to PowerPack
* Discriminated Union code generation provides simpler .NET view

# F# Core Libraries

* Complete the under_score -> camelCase name standardization, of_list -> ofList
* Async API Additions for Web Requests
* Async API Additions for Reactive Applications
* Array2D enables easily creating 2D arrays
* Observable module
* Version-stable serialization of Map and Set
* [.NET 4.0] Lazy, CancellationToken, BigInteger in .NET4.0
* CompiledName used to ensure .NET view is C#/VB friendly

# Visual Studio

* Multitargeting for VS2010: 2.0-4.0 + Silverlight
* Error list improvements
* Much improved debug display of unions and other F# types.
* F1 support

# F# Interactive

* #load .fsx

# F# PowerPack

* Async additions
* FsHtmlDoc.exe

# Miscellaneous

* Deletion of features deprecated in previous F# releases
* Plus many minor fixes and improvements