F# 9 adds nullable reference types

F# 9, the latest version of Microsoft’s open source functional language, has been released with support for nullable reference types and empty-bodied computation expressions. Standard library improvements also are featured, including random sampling functions.

F# 9 was released in conjunction with the .NET 9 software platform on November 12. Instructions on getting started with F#  can be found at dotnet.microsoft.com.

With nullable reference types in F# 9, F# now has a type-safe way to deal with reference types that can have null as a valid value. While F# was designed to avoid null, it nevertheless can creep in with .NET libraries written in C#. F# 9 also introduces support for empty computation expressions. Writing an empty computation expression will result in a call to the computation expression builder’s Zero method. This is a more natural syntax compared to the previously available builder { () }, Microsoft said.

In the FSharp.Core standard library in F# 9, the  List, Array, and Seq modules have new functions for random sampling and shuffling, making F# easier to use for common data science, machine learning, and other scenarios where randomness is needed. Also with the standard library, Shuffle functions return a new collection of the same type and size, with each item in a randomly mixed position. In another standard library improvement, developers now can use C# collection expressions to initialize F# lists and sets from C#.

F# also brings performance improvements. Equality checks now are faster and allocate less memory, and the compiler now generates optimized code for more instances of start..finish and start..step..finish expressions.

Other new features and improvements in F# 9:

• Hash directives now are allowed to take non-string arguments. Previously, hash directives for the compiler only allowed string arguments passed in quotes.
• The #help directive in F# Interactive now shows documentation for a given object or function, which now can be passed without quotes.
• New or improved diagnostic messages or more precise diagnostic locations are featured in F# 9, such as unions with duplicated fields and active pattern argument count mismatch.
• To align with a pattern in some .NET libraries, where extension methods are defined with the same names as intrinsic properties of a type, F# now resolves these extension methods instead of failing the type check.