Sönke Hahn
Chief Technology Officer at Freelance
New York, New York, United States
Summary
🤩
Rockstar🎓
Top SchoolSönke Hahn is a seasoned technology leader and CTO based in New York with 14 years of experience building reliable backend systems and leading engineering teams across startups and large companies. He blends hands-on Haskell expertise—contributing to widely used projects like wai, servant, and hspec—with product-focused leadership roles at Garnix, Twitter, Originate, and ZALORA. Known for improving test coverage, refactoring core APIs, and shipping robust streaming and static-file handling features, he brings a rigorous QA mindset to production services. As a freelance engineer and former director, he balances strategic architecture with frequent code-level contributions, a rare combination that accelerates delivery without sacrificing correctness. Trained with distinction in computer science from Technische Universität Berlin, he often surfaces subtle edge-case fixes that improve real-world reliability.
13 years of coding experience
6 years of employment as a software developer
Diplom, Computer Science, Mit Auszeichnung (with distinction), Diplom, Computer Science, Mit Auszeichnung (with distinction) at Technische Universität Berlin
Github Skills (13)
testing10
api10
servant10
apidoc10
quickcheck10
haskell10
test-automation10
api-design9
restful-api9
rest-api9
file-server9
api-rest9
http9
Programming languages (23)
Github contributions (5)
haskell-servant/servant
Oct 2014 - May 2017
Servant is a Haskell DSL for describing, serving, querying, mocking, documenting web applications and more!
Role in this project:
Back-end Developer & QA Engineer
Back-end Developer & QA EngineerContributions:148 commits, 134 PRs, 333 pushes in 2 years 7 months
Contributions summary:Sönke primarily contributed to the development of back-end components and the improvement of the project's testing capabilities within the Haskell-based servant framework. Their work involved refactoring code by renaming types and functions, and extending the client test suite to cover request bodies, query parameters, and query flags. Furthermore, they added test cases to ensure that the framework correctly handles exceptions during error status codes and implemented a streaming request body functionality. These actions enhance the testing coverage and robustness of the servant framework.
web-applicationsservingqueryinghaskelldsl
hspec/hspec
Mar 2013 - Aug 2016
A Testing Framework for Haskell
Role in this project:QA Engineer / Test Automation Engineer
QA Engineer / Test Automation EngineerContributions:5 reviews, 9 commits, 12 PRs in 3 years 4 months
Contributions summary:Sönke primarily contributed to the testing framework by implementing and modifying tests. This included adding tests for new utility functions (`stdGenToInteger`, `stdGenFromInteger`) and adapting existing tests to incorporate new features. Further contributions involved fixing an issue related to GHCJS compatibility and bumping the version of the testing framework.
smallchecktesting-frameworktestinghaskellquickcheck
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