Formal methods require too much effort for the exotic edge cases they catch — even a simple file-line-counting problem becomes a nightmare to specify.

Real-world specs are a nightmare to write: even a simple problem like 'find the file with the most lines' forces questions about ASCII vs UTF-8, unreadable files, and symlinks. Without formal methods, we can write something correct 99%+ of the time with far less effort. ✦ AI generated

Hillel Wayne · The Pragmatic Engineer · 2026-07-29 · original ↗

It's because specs in the real world are a nightmare to write. Even a simple problem like 'find the file in a directory that has the most lines' gets complicated when modeled with formal methods. We would have to answer questions like: 'do we look at ASCII or UTF-8 new line characters, what about unreadable files, and Symlinks?' Without formal methods, we can write a simple verification that is right in 99%+ of cases. Formal methods require a lot of extra effort for the less than 1% of exotic use cases!

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