Re: list algebra

In message <7iAEc.3599$%_6.3586_at_attbi_s01>, Marshall Spight <mspight_at_dnai.com> writes
>> I like it. A list by definition homogeneous.
>> The somewhat explosive differentiation is pushed to 'type'.
>>
>> It won't suit widely spread ideas on the
>> meaning of the term list, so it must be stated.
>>
>> http://www.swif.uniba.it/lei/foldop/foldoc.cgi?list
>> <quote>
>> A data structure holding many values, possibly of different types,
>> which is usually accessed sequentially, working from the head to
>> to the end of the tail - an "ordered list".
>> This contrasts with a (one-dimensional) array, any element
>> of which can be accessed equally quickly.
>> </quote>
>
>I've long thought those widely spread ideas are crap.
>
>The above definition describes two different implementations
>of list, and ignores the interface question entirely.
>"List" or "sequence" is a mathematical concept
>and it can be implemented in many different ways.
>(In java, this is essentially the difference between
>java.util.List, an interfact, and java.util.LinkedList,
>and java.util.ArrayList. The first is interface; the
>other two are different implementations of that interface.)

And as soon as you start talking MV, that definition is wrong, anyway. In MV, a "dynamic array" is usually accessed sequentially, working from the head to the end of the tail.

 From the programmer's point of view, it is a normal array. From the program's point of view, it's a (funny kind of) list.

Cheers,
Wol

-- 
Anthony W. Youngman - wol at thewolery dot demon dot co dot uk
HEX wondered how much he should tell the Wizards. He felt it would not be a
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as Lies-to-People.
The Science of Discworld : (c) Terry Pratchett 1999