Over here in Germany, we’ve been doing our taxes with Haskell since 2020. Henning Thielemann has been helping us to file a particular type of tax in Germany that is provably unsolvable (a huge system of linear equations with more unknowns than equations, but the tax depends on the solution) and has released a number of Haskell packages during development. He even found and reported bugs in upstream C libraries he was writing FFI bindings for. It was fun to find the minimal example where the tax problem becomes underspecified. The ministry of economics has been informed, but strangely they don’t seem to want to know their law is defunct.
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