On Fri, 19 Apr 2024, Ben via Haskell-Cafe wrote:
I'm not 100% sure what Safe.tailErr function you are using (Hoogle only finds tailErr :: e -> [a] -> Either e [a], which doesn't appear compatible with the way you're using it since it takes an "error message" as first argument).
I found this one: https://hackage.haskell.org/package/safe-0.3.21/docs/Safe.html#v:tailErr It is problematic in even more ways. First, the reader of the code does not know, which tailErr the programmer means. We must look it up. Even if there would be only one candidate, we must look up what it does. Second, the documentation says, tailErr is meant to suppress the new warning on 'tail' in GHC>=9.8, but is still partial. Not a good idea to suppress a warning that has a purpose. Third, the naming of the 'safe' package and 'Safe' module is misleading, because there is nothing unsafe in 'tail'&Co. in the sense of SafeHaskell or unsafePerformIO. 'tail' is partial, that is, for some inputs it is undefined, read: it may run into an infinite loop. But it will not cause memory corruption or ignite nukes while pretending to stay away from IO.