Hi
head []
return Nothing? I guess it's a bit of a silly suggestion, but it helps to highlight why we use Maybe in the first place. So --- where's the cutoff point in your code?
If that is what you want, then see my Safe library: http://www-users.cs.york.ac.uk/~ndm/projects/libraries.php#safe headMay :: [a] -> Maybe a (note this function already exists and is called listToMaybe) However, I think that partial functions are just great, although a lot of people disagree with me. There are some tools being developed to check things like head []: Catch: http://www-users.cs.york.ac.uk/~ndm/projects/catch.php ESC/Haskell: http://www.cl.cam.ac.uk/~nx200/research/escH-hw.ps Catch also checks division by zero, explicit patterns etc. To see the world of pain you would be in if you go down the "make everything total" route, I suggest you try rewriting this program to be complete: http://darcs.haskell.org/nofib/imaginary/digits-of-e2/Main.lhs (if you do, please post the result to the list) If you ignore getArgs and read (which are incomplete in the above example), then Catch is able to prove all the remaining things complete, without annotations or code modifications. You might also want to try redoing that example in the type style, discussed here: http://www.haskell.org/haskellwiki/Non-empty_list Thanks Neil