Computation Expressions in F#

Granted: A good programming language is typically much more than just the sum of its individual features. And yet, sometimes it’s worth taking a closer look: “Computation Expressions” (CEs) from F# are an existing language element that manages to combine flexibility and simplicity in an amazing way.

Sounds like a nice, theoretical little game? They certainly are - and much more: A practical and much-used concept in libraries and in the F# compiler itself. While similar ideas like the “do” notation known from Haskell provide language support for monads, CEs go much further. They allow to reinterpret idiomatic language constructs and give room to control the execution and evaluation for distinct computations themselves.

Compared to alternative concepts such as language macros or compiler plug-ins, CEs do not create “languages within the language” which tend to erode a common “basis of intelligibility” among participating developers. Rather, the original, intentional character of all language constructs from the user’s point of view remains untouched. Hence CEs are a powerful tool that lives in the sweet spot between versatility and quick and easy adoption.

In this tutorial we will show

• how to write a CE from scratch
• what the compiler is doing behind the scenes
• how real world examples work successfully in the industry
• how much fun they can be

Prior knowledge required

To follow the tutorial you need the following prior knowledge:

• basic (functional) programming knowledge
• familiarity with the ML syntax or F# can help but is not a strict requirement

Software Requirements

Please install the latest .NET SDK from https://dotnet.microsoft.com/en-us/download

Verify that you can execute dotnet fsi to start the F# REPL and a simple id 42 works as expected.

For coding F# we recommend VS Code with the Ionide plugin, even though any other editor should suffice.

Please clone https://github.com/dawedawe/bobkonf2024 to have the exercises ready.

David Schaefer

Fediverse: @dawe@fosstodon.org
Twitter: @dawe70704856

I’m David Schaefer, aka dawe, living near Cologne, Germany.

I fell in love with functional programming (FP) while being exposed to theoretical computer science during my time at the university.
After various other jobs, I am a freelancer today and part of the G-Research Open Source team. There, I work full time on the F# open source ecosystem. My main focus is on developer tooling.

Roland Schlenker

Twitter: @SchlenkR
YouTube: @ThePureState

Ronald is a Frankfurt/Germany based programmer with more than 20 years of professional experience. As an expert and recognized member of the F# community, he supports his clients in the design and implementation of complex business applications and technically highly sophisticated libraries. In addition to his day-to-day work for clients, Ronald consults and coaches teams in progressive fields, and he is involved in many successful open source projects like “Vide” (an approach for unified reactive UI development for Web, Avalonia, Maui and others), obscure stuff like “TypeFighter” (a type system (1st order logic), focusing structural types, set theory, and graph based solvers), daily workhorses like “FsHttp”, or audio/music/DSP things like the DSP version of “Vide”.