[Haskell-cafe] Mutable arrays

[Henning Thielemann]

On Sat, 2 Feb 2008, [ISO-8859-7] Jeff ö wrote:

> Hello,
>
> I'm trying to write code that will take a mutable 2D array and normalize it
> by dividing all elements by the largest element.

Are you sure you need the arrays to be mutable? Maybe it's fast enough to
do the copying - it's significantly easier anyway. If all operations run
over the whole array, like the normalization, then it's not much a matter
speed, but only a matter of memory. That is you need the double amount of
memory, because the data can be processed and copied forth and back. You
can even reduce this further, if you can come up with an optimizer fusion
framework.

With immutable arrays you can easily implement
  let xm = maximum (Array.elems arr)
  in  fmap (/xm) arr

Ok, better use the strict "maximum'" proposed by others in this thread.