Fsharp

Parallelising Heterogeneous Async Calls
2025-12-04
This is a post for the FSharp Advent Calendar 2025. A particular feature of F# 10 got me thinking about approaches to parallelism, past and present. Async.Parallel This system library function is built for orchestrating async calls with homogenous return types. It has an overload that permits controlling the degree of parallelism. static member Parallel: computations: seq<Async<'T>> -> Async<'T array> It’s great for situations where we want to make multiple calls to the same api endpoint with different arguments - because each call expects the same response, we end up with a collection of the response type when all the calls are complete. And given the calls are made in parallel, we might only have to wait as long as the longest call. …
fsharp parallelism concurrency async task
RightResult Write Up
2021-04-13
About the design What problem inspired this work? RightResult is the SAAS incarnation of a game my friend would coordinate via emails and a spreadsheet. Each week, he would email game members requesting predictions for the weekend’s English Premier League fixtures. Predictions and fixture results were entered into a spreadsheet. The scores would be tallied-up and communicated back to members. The winner was who had predicted most accurately. I built a product to ease the coordination burden and improve the experience for members. It also serves as a technical laboratory with real challenges. …
elm elmish event-driven event store fable fsharp neo4j
A functional wrapper around the .net AWS DynamoDB SDK
2019-11-29
We’re going to take a tour of some F# capabilities and use them to enforce the constraints of the DynamoDB client. We’ll look at domain modeling with discriminated unions, data access using the reader applicative, and error handling with the result type. DynamoDB and Data Types Before we get started, let’s summarise DynamoDB and its supported types. DynamoDB is a key-value & document database. DynamoDB tables are schemaless so each record can contain a different number of attributes. A record attribute has a string name and a value that is one of three types: Scalar, Set, and Document. A Scalar is a single value of a particular primitive type: string, number, boolean, binary or null. Number and binary values require string conversion before being sent over the network. …
fsharp functional monads aws dynamodb
Combining monads
2019-08-02
The F# Result<'a,'b> type allows for concise control flow syntax. The async { ... } computation expression similarly minimizes the noise of asynchrony. Throw in the Writer monad for logging minus the intrinsic IO statements. How do you get the benefits of all three together? You need to combine… Source code gist. Writer The Result and Async types are core types in F# but Writer is not so we need a bit of boilerplate to get going. We define a single case union type in which the single case is parameterized with a function. The function expects a unit and returns a tuple. See this post for details. …
fsharp functional monads
Scripting with AWS Parameter Store
2018-10-12
Ever need to write a short script as part of development to get feedback on a portion of code? Ever need to add private authentication values to that script? Ever wanted to add the script to source control but couldn’t because it contained your private authentication? Enter: AWS Parameter Store This AWS service acts as a key-value store. Add your private settings such as usernames, passwords, connection strings etc and they can be retrieved programatically by their key name. This lets you commit your handy script to source control by keeping it free from private values. …
aws parameter-store bash fsharp jq