Claus> None of which is satisfactory. You might also want to add
Claus> yourself to this ticket:
Claus> "index out of range" error message regression
Claus> http://hackage.haskell.org/trac/ghc/ticket/2669
How do I do that?
Ghc Trac's idea of voting is by adding yourself to the cc, so that
tickets can be sorted by length of cc list:
http://hackage.haskell.org/trac/ghc/report/17
That is often subverted by closing tickets as duplicate/related,
without transferring the cc list to the one ticket that is kept;-)
Apart from the immediate bug of not getting any information,
there's also the more general issue of wanting information about
the call site (who called which operation, leading to the exception).
A solution to that issue has been sought for a long time, but there
seem to be so many options that the discussion has slowed down
to a halt:
Lexical call site string
http://hackage.haskell.org/trac/ghc/ticket/960
Maintaining an explicit call stack
http://hackage.haskell.org/trac/ghc/wiki/ExplicitCallStack
Using your own wrappers to give you the missing information
is probably the best short-term workaround, but it is no fun.
Something like this, perhaps:
import qualified Data.Array.IArray as A
import Control.Exception
arr ! index = mapException (addErrorInfo (" ! "++show index)) $ arr A.! index
arr // idxs = mapException (addErrorInfo (" // "++show idxs)) $ arr A.// idxs
addErrorInfo info (ErrorCall str) = ErrorCall (str++":"++info)
test1 i = (A.array (1,5) [(i,i)|i<-[1..5]] :: A.Array Int Int) ! i
test2 i = (A.array (1,5) [(i,i)|i<-[1..5]] :: A.Array Int Int) // [(i,0)]
*Main> test1 0
*** Exception: Error in array index: ! 0
*Main> test1 3
3
*Main> test1 8
*** Exception: Error in array index: ! 8
*Main> test2 0
array *** Exception: Error in array index: // [(0,0)]
*Main> test2 4
array (1,5) [(1,1),(2,2),(3,3),(4,0),(5,5)]
*Main> test2 7
array *** Exception: Error in array index: // [(7,0)]
Claus
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