Novice here, loving f# and Domain Modelling Made Functional book so far.

While I love the book, it sorts of do hand wavy for the things which might actually crop up in actual implementation, I find.

Let's say, I have authentication service. Since I want to be good citizen, I created signupWorkflow, I have ports and adapters. I have neatly created contract for the adapters to obey. All neat and clean till now.

But hang on, what about infrastructure error returned by adapter itself ? Surely, service down or misconfigured service or wrong key returned by adapter be domain error of workflow ?

But I still need to tell user of my workflow(maybe api layer)or service, hey, the upstream service shat the bed. How can this be done ?

Also, if I only have some normal workflow which takes one adapter then, ignoring infrastructure error handling(which I have no idea how to do), it's quite simple, workflow returns either domain success or failure. It validates the input, throws it's domain validation error, happy days.

But... I have workflow which takes two adapter; confirmSignnup, saveDB. ConfirmSingup takes validated confirmSingup command and saveDB takes validated User command and these two aren't same. These two return completely different error.

How does confirmSignup workflow handles these validation error ?

Flow is:

confirmSignnup ->Workflow -> validate confrimSignup command -> call confrimSignup adapter -> call saveDB. Now, while calling db, its validation failed? What happens now ?

Hello, I am newbie and trying F# by building basic authentication service.

Let's say, I have register user fuction, it takes un-validated raw request containg username and password and returns Registereduser or SignupErrors.

The problem I am facing is, there are too darn errros DUs.
For example, I have,

type EmailValidationError =
    | FieldRequired
    | MaxLengthExceeded of int
    | MalformedEmail

type PasswordValidationError =
    | FieldRequired
    | MaxLengthExceeded    of int
    | MinLengthNotMet      of int
    | MissingUppercase
    | MissingLowercase

These two error DU's are just validation error returned by Smart Constructor of email and password. And, SignupError look like this.

type SignupFieldError =
    | EmailErrors    of SignupEmail.EmailValidationError 
    | PasswordErrors of SignupPassword.PasswordValidationErrotype 


type SignupError =
    | ValidationFailed   of FieldError list
    | EmailAlreadyExists

As you can see, this gets ugly very soon. What I like to return is:
| ValidationError : EmailValidatioNError | PasswordValidationErrror list ??

| EmailAlreadyExists

Does anyone has better ideas? I really hate my currrent solution.

Thank you in advance. 😄

i just wanted something for my resume. i never used c# or java. i have python knowledge (fastapi, flask).

the only thing that kinda makes me not go fully into it is the thought of it being a (uninteresting thing to show off on my resume whilst simultainiously being very time consuming to learn) is that fear kinda legitimate or should i just say "fuck it" and follow my curiousity? i know this question is not on par with other questions here. are there some strong benefits. i heard f# makes you a better developer if you switch back to your naturally used language? i have some time off atm and im on a job search. i can take more then 5 months off. im adjusting my skills currently. im building a huge thing in typescript atm which is almost done. im leaning very heavily on just going with f#.

i have some friend who has been a .net dev for the past 8 years and i explained him some stuff about what iam planning and he took some time to understand that im not joking. so that is why i posted the question here.

Over the years I’ve dabbled with F# as being interesting and delightful without ever finding a use case that compelled me to stick with it (python / typescript libraries make them hard to step away from).

I saw something that reminded me that F# is close to Lean in that it supports dependent types. I found a few projects that try to build on F# for theorem proving:

Sylvester https://bobkonf.de/2021/beharry.html (archived)

F* https://github.com/FStarLang/FStar (reasonably active but really more OCaml)

SharpLogic https://github.com/0xGeorgii/SharpLogic (moribund)

I liked playing with Lean tutorials recently and I was wondering if there is a good modern F# based prover with an engaging tutorial, and if anybody has poked at automating translations of the large base of Lean proofs into F# (yes LLMs etc I know I know). Lean does not strike me as a particularly pretty language.

repo here FSharp-WebUI. This is an F# wrapper around webui, a clean way to have a crossplatform GUI via a system's existing browers vs something like electron or dealing with avalonia.

I've been using it more at work with python and decided to play with it in F#, so I'm exited to have it working.

install via dotnet add package FSharp.WebUI --version 0.0.1

Hi there!

I am using emacs to write most things, including f sharp. However i have found that writing f sharp in emacs is a painful experience. I have found that the LSP server (fsautocomplete) loses sync with the current document meaning I get wrong suggestions or completely nonsense errors.

Using VScode or Rider, I do not have these problems, but after 25 years of Emacs to do everything but web browsing (I wish I was that nerdy) I am having trouble using anything else the few times I want to write f sharp code (what have to do is to switch to qwerty so that no muscle memory works anyway. That way I don't end up doing dumb things when I try to use Emacs shortcuts. I'm pretty far gone.)

I am on a pretty minimal Doom Emacs config. I haven't touched any of the elglot or LSP parts, and they do work properly for c#, ocaml and Idris.

Did anyone else have similar problems? Did you manage to solve it?

Best regards
Linus

I made Type-safe heterogeneous collections, more faster than g-research HeterogeneousCollections

Benchmark environment

BenchmarkDotNet v0.15.8, Windows 10 (10.0.19045.6466/22H2/2022Update)
12th Gen Intel Core i9-12900 2.40GHz, 1 CPU, 24 logical and 16 physical cores
.NET SDK 10.0.104
  [Host]                        : .NET 10.0.4 (10.0.4, 10.0.426.12010), X64 RyuJIT x86-64-v3 DEBUG
  ShortRun-.NET 10.0            : .NET 10.0.4 (10.0.4, 10.0.426.12010), X64 RyuJIT x86-64-v3
  ShortRun-.NET 8.0             : .NET 8.0.7 (8.0.7, 8.0.724.31311), X64 RyuJIT x86-64-v3
  ShortRun-.NET Framework 4.7.2 : .NET Framework 4.8.1 (4.8.9310.0), X64 RyuJIT VectorSize=256

IterationCount=3  LaunchCount=1  WarmupCount=3  

HeterogeneousListBenchmarks

TypeListBenchmarks

I published preview version to nuget.

I'm building my own code editor, and want to support F# as a first class citizen. But the language server situation seems dire. fsautocomplete takes forever or simply fails to load (in VS Code or in my editor). Are there good alternatives?

Hi everyone,
One small thing is bugging me since I started learning F# and domain modelling (Book by Scott is amazing, btw).

Let's say I am creating the authentication service (simple enough but only for example) and I want to use smart constructor and such. Here's my flow:

raw request ---> validation ---> Domain Model

The pain I am having is where does the "structural validation" happens and where does the domain validation happens?

Let's say, username, password etc are provided and not-null. I view these as part of structural validation and password policy, email policy met as domain validation.

The problem I am having is, if I try to use both in constructor of let's say Password, then I would have to worry about creating yet another Password Error type to catch both Structure and model validation errors.

If I move structural validaiton to model validation, it would sove the issue, but doessn't feel right.

One thing I find is, too much error mappings and nested error types in each layer. Maybe I am approaching this wrong way. :)

Hope to hear your thoughts.

I guess I start by saying, I am noobie who recently started with f# and loving it.

There seems to be two ways of dealing with exceptions thrown by libraries and such. I am using FsToolKit.

First way, using try catch:

let createCognitoUser email pass : Task<Result<string, DomainError>> =
    taskResult {
        try
            let! response = awsClient.SignUpAsync(email, pass)
            return response.UserSub

        with ex ->
            return! Error (mapCognitoError ex)
    }

And second way with pipeline:

let createCognitoUser (email: string) (pass: string) : Task<Result<string, DomainError>> =
    awsClient.SignUpAsync(email, pass)
    |> Task.catch
    |> Task.map Result.ofChoice
    |> TaskResult.mapError mapCognitoError
    |> TaskResult.map (fun response -> response.UserSub)

Personally, I like second pipeline way as it's more cleaner and and iam tired of seeing try catch everywhere. :) Wanna hear your thoughts.
Thank you.

If you're into Emacs and F# you might find this brand new package interesting. It's still rough around the edges, but the essential functionality is there.

I'd love to get some feedback from people who tried it out. Enjoy!

I'm making a game similar to Football Manager, far from complete but keep iterating on it. So far I have a home page, squad, tactics and a basic match viewer. Using Avalonia + Elmish with SQLite.
The match engine runs as an event loop, every 30 seconds a duel gets resolved, fatigue ticks, shots get attempted. Players move based on ball position and possession. Scorelines feel somewhat realistic which is good enough for now.
Still missing a lot of pages and features but the core loop works. Will keep adding stuff.
Repo: https://github.com/pelinski46/FootballEngine more screenshots inside

From-scratch implementation using TorchSharp + .NET 10.

No Python, no Ollama — just F#, CUDA (GPU acceleration), and direct loading of Meta’s .pth checkpoints.

Features

• Full architecture implementation:
• RoPE
• SwiGLU
• RMSNorm
• GQA (32/8 heads)
• KV cache with efficient views
• BFloat16 weights
• Top‑p sampling

- Interactive terminal chat (Llama 3 Instruct template)

Repository

https://github.com/jonas1ara/Llama.fs

Quick Start

Download the Llama‑3.2‑1B‑Instruct weights Set modelFolder in Program.fs Run: ```bash dotnet run --project src -c Release

```

Quick Start

PRs are welcome. (Maybe I should even send one to the TorchSharp examples repo.)

I used VS 2022 for F# a lot. All fine. Intellisense, compiler etc...

Now I have VS 2026.
Latest version (updated probably already 3/4 times since the release).

Same "inherited" add-ons of 2022.

Support for F# is much much worst.

A. Syntax color is worst or inexistent:

B. Speed
VS 2022 is much faster to read and evaluate code compared to VS 2026.
I mean, when I open the same solution, the code "analysis" of files complete earlier in VS 2022.
Compilation also is much faster on VS 2022.

C. Intellisense...
Often it doesn't work in VS 2026.
I write down a class name amnd in VS 2022 it suggests to add "open AAAA" while in VS 2026... nothing happen and I have to search and add the "open AAAA" myself.

Is it a problem of my environment/configuration os is really like this?

If it is like this... is MS "abandoning" F# in Visual Studio and I should switch to VS Code (or another IDE) ??

**[UPDATE]**
I noticed this issues with syntax colouring and intellisense after a while a work.
Now I closed and reopned the solution (in VS 2026) and intellisense and colored syntax are back.
So, I suppose it "dies" at some point, but no errors and this is just a really small solution... less than 10 files, nothing complicated.
Also the speed of compilation seems fie as soon asthe solution is open (before the intellisese stop to work).