On Fri, 7 Jan 2005, Simon Peyton-Jones wrote:
| * As far as I can determine, there is no way to check pattern matches for | exhaustiveness. Coming from OCaml, this feels like losing a significant | safety net! How do people program so as not to be getting dynamic match | failures all the time?
GHC has -fwarn-incomplete-patterns and -fwarn-overlapped-patterns. But the code implementing these checks is old and crufty, and the warnings are sometimes a bit wrong -- at least when guards and numeric literals are involved. I think they are accurate when you are just using "ordinary" pattern matching.
Cleaning up this bit of GHC is a long-standing to-do item, if anyone feels motivated to undertake it. It's a well-defined task, with plenty of well-written papers explaining how to do it -- but it's tricker than it seems at first!
What about dropping Guards? :-) Are they necessary? Do they lead to more readable source code? Do they lead to more efficient code? I could perfectly live without them up to now.