> I was talking about the "last" function in my original comment. Then let's say that "some_input" is a list and the non-IO function "compute_directory_name" s

> I was talking about the "last" function in my original comment. Then let's say that "some_input" is a list and the non-IO function "compute_directory_name" should return the last element of that list. If that code were instead a part of the IO function "rmrf_steamroot" then the code would have just as many bugs. Conversely, extracting code from an IO function into a non-IO function proves only that the code did not perform IO (and therefore did not have IO bugs) in the first place. There is no bug reduction. > I did enumerate every possible way that function can go wrong in Haskell. This is deduction. > "active acquisition of information from a primary source" Did you read beyond the first sentence of that article? "In living beings, observation employs the senses." Which senses did you use to deduce the number of ways a function can return an element of a list? > i.e. observational evidence No, a mathematical "observation" is not an empirical observation. > So we take whatever evidence we can get. We all do! But you have no evidence at all.