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What's New in F# 4.7

Functional programming devotees welcomed the general availability of F# 4.7 yesterday (Sept. 23) along with the release of .NET Core 3.0 and its associated tooling.

The open source F#, developed entirely via an open requests for comments (RFC) process, sees compiler and core library infrastructure changes and syntax tweaking.

One notable change in the new release is that FSharp.Core now targets .NET Standard 2.0. Microsoft's .NET Standard provides a spec of .NET APIs that should be available on all .NET implementations. "Starting with FSharp.Core 4.7.0 and F# 4.7, we're officially dropping support for .NET Standard 1.6," said Phillip Carter, program manager for .NET and Languages, in an announcement post. "Now that FSharp.Core targets .NET Standard 2.0, you can enjoy a few new goodies on .NET Core:
  • Simpler dependencies, especially if using a tool like Paket
  • FromConverter and ToConverter static methods on FSharpFunc<'t, 'tresult="">
  • Implicit conversions between FSharpFunc<'t, 'tresult=""> and Converter<'t, 'tresult="">
  • The FuncConvert.ToFSharpFunc<'t> method
  • Access to the MatchFailureException type
  • The WebExtensions namespace for working with older web APIs in an F#-friendly way

Also, the F# interactive (FSI) can be used from .NET Core in a preview. It enables developers to run F# code interactively in the console, or to execute F# scripts.

"The FSI experience for .NET Core is now a very, very stable preview," Carter said. "There are still some quirks with dependency resolution when pulling in packages and their transitive references. We're addressing these by adding #r "nuget:package-name" support for FSI, and we're hoping that you'll transition away from manually referencing third-party .dlls and instead using packages as the unit of reference for FSI."

Other highlights of F# 4.7 include:

  • Support for LangVersion: "F# 4.7 introduces the ability to tune your effective language version with your compiler."
  • Implicit yields: "In the spirit of making things easier, F# 4.7 introduces implicit yields for lists, arrays, sequences, and any Computation Expression that defines the Yield, Combine, Delay, and Zero members."
  • Syntax relaxations: "There are two major relaxations for F# syntax added in F# 4.7. Both should make F# code easier to write, especially for beginners."
  • Indentation relaxations for parameters passed to constructors and static methods.
  • A couple of preview features: Nameof and open static classes.

Going forward toward F# 5 and .NET 5, a unification of all the fragmented .NET implementations, Carter noted work on making F# a first-class language for Jupyter Notebooks via the .NET Kernel and emphasizing language features to make it easier to work with data collections.

"As .NET undergoes a monumental shift towards .NET 5, F# will also feature a bit of a shift," Carter said. "While F# is a general-purpose language -- the functional programming language for .NET -- it also has a strong heritage of being used for 'analytical' workloads: processing data, doing numerical work, data science and machine learning, etc. We feel that F# is positioned extremely well to continue this path, and we intend on emphasizing features that can align with these workloads more."

About the Author

David Ramel is an editor and writer for Converge360.

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