Contains vs is in

Ali Lloyd ali.lloyd at livecode.com
Wed Jan 4 11:16:36 CET 2017


'contains' and 'is in' are implemented exactly the same in LiveCode Script,
so there shouldn't be any difference. However there is an interesting
subtlety that emerges when you consider what these two bits of syntax
should do, which explains why they are different in LCB.

When we say 'A contains B' where A is some sort of sequence (ordered set),
then I would argue we really mean that B is a subsequence of A. On the
other hand I think the interpretation of 'is in' is the same as that of 'is
among the elements of'.

Thus 'contains' is actually a relation between sequences and sequences,
whereas 'is in' is one between elements and sequences. This makes no
difference in LCS for strings because the type of the sequence is the same
as the type of the element, namely they are strings. However it does mean
that the following two should be considered anomalous:

1) In LCS, 'is in' does not restrict the left hand side to a single char
2) In LCS, no string other than empty 'contains' empty

Both of these anomalies are rectified in LCB. The situation becomes clearer
when using an LCB list, where <list> contains <string> is a syntax error,
and <listA> is in <listB> is only true if listA occurs as an *element* of
listB, rather than a subsequence. Moreover <list> contains [] is always
true.


tl;dr - there should be no performance difference between 'contains' and
'is in' in LCS.

On Tue, Jan 3, 2017 at 11:35 PM Bob Sneidar <bobsneidar at iotecdigital.com>
wrote:

> I interact with copier interfaces quite a lot and the process of backing
> up the data involves going through various pages and typing what I see
> there into a text file. I have always thought it would be great to write an
> app that can do it for me, but I have never been able to scrape anything
> more than the HTML text displayed on the page.
>
> I will have to look into ways to use Javascript to do it. If it requires
> already knowing what the values are though, I'm afraid I might meet with
> unsurpassable difficluty.
>
> Bob S
>
>
> On Jan 3, 2017, at 15:02 , Mike Kerner <MikeKerner at roadrunner.com<mailto:
> MikeKerner at roadrunner.com>> wrote:
>
> the short answer is "yes", but it can be more complicated as it may require
> some javascript execution to pull the data from the server.  It depends on
> the site you are scraping.  You can also (possibly) use a service that can
> yank that for you.
>
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