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Sem Postma

Senior Software Engineer | TypeScript | Distributed Systems

sem@sem-postma.nl

+31 (0)6 405 660 04

Profile image

.About

I'm a software engineer with 10 years of professional experience building production systems, specializing in TypeScript, functional programming, and cloud infrastructure.

Current Focus

  • Effect-TS & Functional Programming — Building type-safe distributed systems using concepts from category theory
  • AWS Infrastructure — Lambda, DynamoDB, CDK, and serverless architecture
  • Kubernetes — Self-hosted infrastructure and cloud-native platforms
  • Security & Compliance — Experience with security-conscious environments and accessibility standards

Recent Work

I build enterprise systems with Effect-TS on AWS. I've also delivered accessibility-compliant projects for government clients under NDA.

I value working with teams that prioritize technical excellence and aren't afraid to adopt modern approaches when they provide real benefits.

AWS Certified Solutions Architect

.My Values

I think it's important to always be myself and to be honest. This impacts everything I do, from the way I work to how I treat people.


  • Open, reliable and down to earth
  • Genuinely passionate about the craft
  • Focused on results that hold up
  • Happy to share what I know with the people around me
  • Willing to throw myself in the deep end
  • Open to feedback and criticism

.Recommendations

"Sem was very patient through the entire process. He was quick to understand the requirements and picked up with minimal explanations needed. Perfect team member to work with. Will hire again."

— Mridul Pandey (Inventam)

"Amazing work!"

— Hansen Wang

"Very nice to work with Sem. Sem is quick to pick up what I want. He really listens and translates that into his work."

— Claudia Mulder

.Technical Expertise

  • Core Stack - TypeScript | Effect-TS | Node.js | React | AWS
  • Cloud & Infrastructure - AWS (Lambda, DynamoDB, CDK, S3, CloudFront) | Kubernetes | Terraform | Cloudflare Workers (D1, R2, KV) | Docker
  • Databases - NoSQL | SQL | KV
  • Mobile - Kotlin Multiplatform (KMP) | Swift | Flutter | Cordova
  • Methodologies - DDD | TDD | BDD | Unit Testing | Integration Testing | CI/CD | Agile | Scrum
  • Architecture - Microservices | Event-Driven | Serverless | Clean Architecture | CQRS
  • Security & Compliance - Information Security | WCAG Accessibility | Secure Development Practices
  • Certifications - AWS Solutions Architect (Associate)
  • Languages - English (Fluent) | Dutch (Native)
Me as a child
Me as a child
Me as a child

.Interests

Functional Programming, Category Theory, Type Systems, Domain-Driven Design, Test-Driven Development, Event Sourcing, Distributed Systems, Concurrency, Parallelism, Reactive Programming, Design Patterns, Clean Code, Software Architecture

.ATC Manager 2

Case — Built with Preact

ATC Manager 2 is a web based air traffic control game. Manage airspace of busy airports like Schiphol or Heathrow in a realistic simulator.

.Laika CMS

Case — Built with React, Redux, Express, PostgreSQL, Redis, AWS

A custom built content management system.

.Kadaster Kaart

Case — Built with Cordova

With the "Kadaster Kaart" App you can easily look up information about plots that are registered with the Land Registry.

You can view information about locations, berths, residences, properties and plots. The App has an easy-to-use interface.

.duurzaamgeertruidenberg.nl

Case — Built with PHP

The client's goal was to create a Municipality website for sustainability.

With the adobe XD design in hand, I implemented everything accurately.

The client was very happy with the end-result. Visually the website looks great and the designer was pleased that we implemented every small animation and detail correctly.

The website is also WCAG 2.1 AAA compliant.

Visit duurzaamgeertruidenberg.nl

.Imagineers by Night

Case — Built with Kotlin and Swift

The goal for this project was to design an app that could help people find their way across the city of Breda during the Imagineers by Night event.

The app is written in Kotlin (Android) and Swift (iOS) and keeps to the redux state management principles.

I have personally contributed to the project by expanding functionality and transitioning the app to use the new JSON:API/OpenAPI backend.

.Cast to Sonos

Case — Built with TypeScript as a Chrome Extension

Cast to Sonos is a browser extension that streams audio from any web page directly to your Sonos speakers — filling a gap in Sonos functionality much like Chromecast does for other devices.

With one click you can cast YouTube, Twitch, podcasts, streaming music and any HTML5 audio player to your speakers. It streams locally over your network to S2-platform Sonos devices and automatically synchronises video and audio to compensate for streaming delay.

The extension uses a freemium model with stereo and Hi-Fi quality tiers and multi-room support, and works on Windows, macOS, Linux and ChromeOS.

Visit casttosonos.com