Hi
1. Allow empty case, i.e. "case some_variable of { }" (GHC ticket [1]). This adds consistency, it always causes a pattern-match error, and it is a sensible way to look at all the cases of types with no constructors (recall EmptyDataDecls will probably be in Haskell' [4]) -- especially for automatic tools (or programmers familiar with dependent types; GADTs have some of these effects :-)). Presumably, any time that some_variable could be non-bottom, GHC will warn about the incomplete patterns :-).
Sounds good. Great for consistency and auto-generation of code.
2. When a type signature for a function is given, allow to not define any patterns (GHC ticket [2]). The result of calling the function is a pattern match failure (presumably the source-location given for the match failure will be the location of the type-signature). This can also be useful for calling functions before implementing them, helping the type-checker help me do incremental work (again, obviously produces a warning if the function could possibly be non-bottom).
Sounds bad. Consider: gray :: Color grey = newColor "#ccc" This fairly common style of bug now becomes perfectly valid Haskell, and if you always refer to "grey", you may never even have a clue that the bug is present. Thanks Neil