[Om] Tuple and list : any distinction?
Joe Collins
joseph.collins at nrl.navy.mil
Thu Feb 18 18:56:15 CET 2010
Dear Michael,
Most of what you write is roughly consistent with what I have understood, and
helps a little more with the OpenMath flavor.
I was a little thrown by "Semantics of OpenMath and MathML3", Kohlhase & Rabe,
where:
Definition 3 (OM Context). An OM context C is an n-tuple of variables
which we will write as <x1 , . . . , xn >. We will use + for tuple
concatenation and $\in$ for tuple membership.
implies tuple concatenation is normal.
(Sorry, I didn't mean to knock you for inconsistency).
Let me, however, get straight to my real concern.
I want to represent a coordinate variable tuple like (X, Y, Z) or
(r, theta, phi). I do NOT consider these "vectors" in general.
I was considering using tuple to construct them, but then needed a
means of indexing them. Either adding a "tuple_selector" symbol or using the
existing list symbols seemed to be the two best options, with my preference
towards the "tuple_selector" symbol.
After this feedback on the OpenMath flavor of things, my preference has
increased in that direction.
If you ask "Why not 'vectors'?", I'll ask
"What does it mean to add
(r1, theata1, phi1) + (r2, theata2, phi2) ?".
(Things aren't sufficiently interesting if you stay in Cartesian coordinates!)
Regards,
Joe
Michael Kohlhase wrote:
> Dear Joe,
>
> there are at least two possible answers to this question:
>
> Mathematical:
>
> generally spoken, tuples and lists are isomorphic as data raw
> structures, but support conceptually different operations. Tuples are
> usually thought of as having fixed length and operations are between
> tuples of same length. Operations are mostly from linear algebra. In the
> ecc CD we have dependent tuples that are mostly used for defining
> functions.
>
> Lists are thought of as of variable length, and the operations are
> mostly constructing lists from the empty list by prepending, appending
> lists, mapping functions over lists,.... Moreover, lists typically only
> have members of the same "type".
>
> So, even though everything you do with tuples, the mathematical,
> operational intuitions are quite different.
>
> Formally:
>
> The levels of formality in the descirption of ecc and list1/2 are vastly
> different. ECC (Extended Calculus of Construction) is a logical system,
> where tupling has a very well-defined role. list1/2 is a (intendedly)
> vague description of a vocabulary of lists without going into too much
> detail, so that it can be universally used.
>
> hope this helps,
>
> Michael
>
> On 17.02.10 14:51, Joe Collins wrote:
>> The OpenMath ecc CD defines Tuple and the list1 CD defines list.
>>
>> Is there any essential distinction between Tuple and list?
>> If so, what?
>>
>> Some of the definitions in list1, list2 suggest (to me) that the order
>> of the
>> list elements are arbitrary. Is this actually the case?
>>
>> Joe
>>
>
--
_______________________________
Joseph B. Collins, Ph.D.
Code 5583, Adv. Info. Tech.
Naval Research Laboratory
Washington, DC 20375
(202) 404-7041
(202) 767-1122 (fax)
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