Arrays allow out-of-bounds indexes

The array changes proposed and recently implemented for ticket #1610 (closed) (Make arrays safer) strengthened the requirements on Ix instances, but weakened the requirements on array users. Specifically, array referencing now permits indexes that are not inRange.

For example,

import Data.Array.IArray

b :: Array (Int,Int) Int
b = listArray ((0,0), (3,3)) (repeat 0)

main = do
  print (b ! (0,5))              -- SHOULD fail, but doesn't
  print (index (bounds b) (0,5)) -- DOES fail

The first line in main should fail because the specified index is not inRange, but doesn't because the (!) operator (specifically Data.Array.Base.safeIndex) now uses unsafeIndex and simply checks that the resulting index is within the linearized bounds of the array. In this case, the unsafe index of (0,5) wraps aroung to the index of (1,1).

A simple fix would be to use index instead of unsafeIndex in the implementation of Data.Array.Base.safeIndex. This would both require the user to use in-bounds references and would require Ix instances to return in-bounds indexes.

Trac metadata

Trac field	Value
Version	6.8.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	libraries (other)
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system	Multiple
Architecture	Multiple