I agree that this is very annoying (and time consuming!) time for debugging, as it has implicit assumption about data (e.g. that some column has more than one v

I agree that this is very annoying (and time consuming!) time for debugging, as it has implicit assumption about data (e.g. that some column has more than one value). I was tempted a few time to write pipelines in Python which make such sanity-checks. In any case - thanks for sharing your example. By any chance, can you show an example for such Haskell pipeline? (Especially if there is some non-trivial statistics, or ML training.)