Here&#x27;s an example where I used, if not the Yoneda lemma, its categorical dual the co-Yoneda lemma (named `MarketRequest` in this post because I didn&#x27;t know about it at that point so had to reinvent it to my particular use case) to solve a very real software engineering problem: <a href="http:&#x2F;&#x2F;unsafePerform.IO&#x2F;blog&#x2F;2012-12-01-static_analysis_with_applicatives&#x2F;" rel="nofollow">http:&#x2F;&#x2F;unsafePerform.IO&#x2F;blog&#x2F;2012-12-01-static_analysis_with...</a>