Re: Aggregation (with GBY) is Relational Division

From: Frank Hamersley <terabitemightbe_at_bigpond.com>
Date: Wed, 07 Jun 2006 14:08:03 GMT
Message-ID: <75Bhg.5116$ap3.901@news-server.bigpond.net.au>

vc wrote:
> Frank Hamersley wrote:

>> vc wrote:

>

>>>>
>>>>    eg> foldr (+) 4 [1..3]   produce 4+3+2+1 or 3+2+1+4?
>>> foldr (+) 4 [1..3]   =>  1 + (2 + (3 +4)) = 10

>

>> or
>>
>>    foldr (+) 4 [1..3]   =>  1 + (2 + (4 + 3)) = 10

>
> No.
>

>> or
>>
>>    foldr (+) 4 [1..3]   =>  (((4 + 3) + 2) + 1) = 10

>
> No.
>

>> ???

>
> Take any non-commutative operation to see the difference.

Drat - I knew the operator itself would become the point of focus! What I wanted to know was the order in which the list elements would be addressed - then I can work out the trivial details surrounding the commutative or non-commutative operators that I might choose.

Cheers, Frank. Received on Wed Jun 07 2006 - 09:08:03 CDT