[Haskell-cafe] What's the deal with Clean?

[Gregory Crosswhite]

Oh, that's strange...  the type class "UA" is defined twice, once in  
Data.Array.Vector and once in Data.Array.Vector.UArr;  in the first  
module indexU is a separate function with the sources I exhibited, in  
the second module it is a method of the UA type-class which seems to  
have O(1) access for most of the defined instances.

That's incredibly confusing...

- Greg


On Nov 3, 2009, at 9:15 PM, Don Stewart wrote:

> Well, it depends on which indexU the OP means. The one linked in the  
> docs is
> the O(1) UA type class version.
>
> -- Don
>
> gcross:
>> Actually, it's not a typo.  If you look at the source, what you'll  
>> see
>> is
>>
>> indexU arr n = indexS (streamU arr) n
>>
>> and then tracking down indexS, you'll see
>>
>>
>> indexS (Stream next s0 _) n0
>>    | n0 < 0    = error "Data.Array.Vector.Stream.indexS: negative
>> index"
>>    | otherwise = loop_index n0 s0
>>  where
>>    loop_index n s = case next s of
>>      Yield x s' | n == 0    -> x
>>                 | otherwise -> s' `seq` loop_index (n-1) s'
>>      Skip    s'             -> s' `seq` loop_index  n    s'
>>      Done                   -> error  
>> "Data.Array.Vector.Stream.indexS:
>> index too large"
>>
>>
>> So in other words, indexU really does have O(n) complexity since it
>> first converts the array into a stream and then walks down the  
>> stream in
>> order to find the desired element.
>>
>> Cheers,
>> Greg
>>
>>
>> On Nov 3, 2009, at 6:25 PM, Roman Leshchinskiy wrote:
>>
>>> On 04/11/2009, at 13:12, brian wrote:
>>>
>>>> indexU :: UA e => UArr e -> Int -> e
>>>>
>>>> O(n). indexU extracts an element out of an immutable unboxed array.
>>>
>>> This is a typo (unless Don inserted a nop loop into the original DPH
>>> code).
>>>
>>> Roman
>>>
>>>
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