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Summary:
* The F# Visual Studio project system and language service have been completely re-implemented.
* F# Project Files now use suffix .fsproj and support MSBuild.
* F# Interactive in Visual Studio has been greatly enhanced as a tool window. The menu item is now under View -> Other Windows
* Enhanced scripting support
* The F# language now supports "Units of Measure" checking and inference
* The command line options for the F# compiler have been simplified and aligned with standard .NET practice, though retain the -- notation.
* The F# library is split into two components. FSharp.Core.dll: Contains the core F# libraries, which will be stabilized and versioned infrequently. FSharp.PowerPack.dll: Contains additional useful F# libraries and tools which will version more frequently, and allow continued innovation on top of the core F# language and libraries. The fslex and fsyacc tools are part of the F# PowerPack.
* .NET 1.x is no longer supported. .NET 2.0 or above is needed by this version of the F# compiler and runtime libraries.
* The F# Visual Studio integration now requires Visual Studio 2008 (and may be used with the freely available Visual Studio 2008 Shell).
* #light or #light "off" required in .fs, .fsx and .fsi files
* "AutoOpen" attribute now supported
* F# functions whose inferred type includes an unsealed type in argument position may now be passed subtypes when called, without the need for explicit upcasts.
* Sequence and computation expression syntax regularization and simplification
* Improvements to debugging and stepping (requires tailcalls be explicitly disabled)
* Simplified event creation and publication
* Simplified Reflection API
* Simplified quotation language feature and API
* Namespace abbreviations now deprecated
* Language improvements for better software engineering practice
* F# now respects COM automation optional and default parameters
* Operator resolution defaults to resolving to operators defined as static members in relevant argument types if no other definition of the operator is given
* PowerPack support for quotation compilation and evaluation via LINQ expression trees
* The PowerPack lexer generator tool 'fslex' now supports Unicode inputs
* PowerPack support for query evaluation via LINQ expression Trees
* Deletion of features deprecated in previous F# releases