On Wed, Dec 06, 2006 at 07:50:30AM +0000, Simon Peyton-Jones wrote:
I rather agree with Iavor here. If a program makes no use of unsafeX functions, and has no foreign calls, and passes the typechecker, then it should not crash.
However, I don't see how to achieve this for array indexing, without adding another test to every array access.
If we allow inRange to return anything at all if the result of index is out-of-bounds, then the standard Ix instances lose one test for each access; e.g. the Int instance can return constant True for inRange because any invalid index would give an invalid result. Obviously, this makes inRange into a rather low level operation that should be renamed and wrapped (with a function that always gives the right answer).