2 Sep
2005
2 Sep
'05
3:10 a.m.
... It's very hard to debug a large program when you can randomly get messages like "*** Exception: Prelude.head: empty list" and have no idea where they came from.
As a purely pragmatic suggestion: don't use head, fromJust, last, or any other function that is likely to fail in impossible-to-find way, at least not directly. In GHC, you can wrap or replace them with irrefutable patterns which are almost as easy to write, and will give you a sensible error message if they fail. Example: replace x = head xx with (x:_) = xx replace x = fromJust mX with (Just x) = mX replace x = last xx with y@(_:_) = xx x = last y Ben.