Re: [Haskell-cafe] Error in array index.

Am Mittwoch 24 Juni 2009 18:50:49 schrieb Jason Dusek:

2009/06/24 Ketil Malde :

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Bulat Ziganshin writes:

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    array ((0,0),(65535,65535)) [((0,0),*** Exception: Error in array index

i think that it may be a bit too large for internal Int indicies:

Aren't you asking for a 4G element array here, so with a 32bit wraparound the array will be some multiple of 4GB

It's a bit array. It'd be 512MiB.

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So in effect, you have a zero-length underlying array, but the array implementation still keeps track of the real indices and tries to print some contents.  (Correct?)

I don't quite understand your reasoning here.

The 'length' of the array, as in 'number of elements' is calculated by multiplying the lengths in each dimension sz = rangeSize d1 * rangeSize d2 rangeSize (0,65535) = 2^16 (2^16)^2 = 2^32 2^32 :: Int = 0 on 32-bit systems I don't know if that's how it's implemented, but that's the reasoning leading to an array of size 0.

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Since array dereferencing are now checked against the underlying array instead of the real indices, you get this kind of inconsistency.  It is greatly surprising to me that this has not been fixed.

As long as 'unsafeAt' gives you the speed without the safety, I don't think the default dereferencing shouldn't sacrifice helpful error messages and predicability.

This arrangement would make me LOL if it weren't my own project...

-- Jason Dusek