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#1
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confused by match semantics and $0 var



Postby bairui » Mon Jul 23, 2012 9:10 am

I've either found a bug in NL (10.4.3) or, more likely, a bug in my understanding of how its match semantics and the $0 variable work. In particular, I am having trouble with an example on the NL wikibooks site:



http://en.wikibooks.org/wiki/Introducti">http://en.wikibooks.org/wiki/Introducti ... et-ref-all



Given a sample list:



Code: Select all

    (set 'planets '(("Mercury" (p-name "Mercury") (diameter 0.382) (moons 0))("Venus" (p-name "Venus")(diameter 0.949)(moons 10))("Earth" (p-name "Earth")(diameter 1)(moons 1))))







The example on the wiki page is:



Code: Select all

    (set-ref-all '(moons ?) planets (if (> (last $0) 9) "lots" (last $0)) match)







But that doesn't seem to work for me. This seems to instead:



Code: Select all

    (set-ref-all '(moons ?) planets (if (> (last $it) 9) '(moons "lots") $it) match)







I am confused with what is supposed to be stored in the $0 variable. It seems that the [*+?] capture is being ignored and $0 is being set to 1 regardless of the actual value in the list.



Code: Select all

    (set-ref-all '(moons ?) planets $0 match)







Results in:



Code: Select all

    (("Mercury" (p-name "Mercury") (diameter 0.382) (moons 1)) ("Venus" (p-name "Venus") (diameter 0.949) (moons 1)) ("Earth" (p-name "Earth") (diameter 1) (moons 1)))







Where the (moons 1) sublists boggle me. What have I missed here?



bairui

     

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Re: confused by match semantics and $0 var



Postby cormullion » Mon Jul 23, 2012 10:53 am

I think the wikibook is wrong. In newLISP version 9, I think the code worked as written, but I can't remember when $it was introduced. However, there are still some lingering errors in the wikibook, and you've found one of them. Sorry - but congratulations anyway... :)



To preserve the spirit of the original, you could probably use:



Code: Select all

    (set-ref-all '(moons ?) planets (if (> (last $it) 9) '(moons "lots")  $it) match)







But perhaps the whole section should be rewritten.



cormullion

     

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Re: confused by match semantics and $0 var



Postby bairui » Mon Jul 23, 2012 12:34 pm

Thanks, cormullion,



I gather you did most of the NL wikibook work. Awesome job, mate. I suspected the few glitches I've found along the way were due to API/lib changes as NL marched along. That's fair. It would be good to keep the wikibook resource as up to date there as we can. I patched it in a few small places today, but as I'm new to NL and lisp in general, I am hesitant to make bold changes.



I am still confused about the differences between $0 and $it. It seems that $it is working the way $0 did for you in version 9 (I came to NL only after it was well into version 10). $0 on the other hand seems... broken to my mind. I am happy to assume the breakage there is all mine though, so I'd like an explanation of how it works. (Lutz?)



bairui

     

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Re: confused by match semantics and $0 var



Postby Lutz » Mon Jul 23, 2012 2:26 pm

In set-ref-all the $0 variable is only set when regular expressions are involved. But $it is always set. The following example works with both $0 and $it



Code: Select all

    > (set-ref-all ".*m.*" '("abmcd" "defg" "xymzw") (upper-case $0) regex)

    ("ABMCD" "defg" "XYMZW")



    > (set-ref-all ".*m.*" '("abmcd" "defg" "xymzw") (upper-case $it) regex)

    ("ABMCD" "defg" "XYMZW")

    >







All strings containing an "m" are upper-cased.



See also here for an explanation of anaphoric $it and other system variables:



http://www.newlisp.org/downloads/newlis">http://www.newlisp.org/downloads/newlis ... em_symbols



Lutz

     

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Re: confused by match semantics and $0 var



Postby bairui » Mon Jul 23, 2012 2:39 pm

Thanks, Lutz.



Interestingly, $0 and $it behave differently when the regex matches less than the element:



Code: Select all

    > (set-ref-all "m" '("abmcd" "defg" "xymzw") (upper-case $0) regex)

    ; ("M" "defg" "M")

    > (set-ref-all "m" '("abmcd" "defg" "xymzw") (upper-case $it) regex)

    ; ("ABMCD" "defg" "XYMZW")



bairui

     

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Re: confused by match semantics and $0 var



Postby Lutz » Mon Jul 23, 2012 3:01 pm

Yes, because $0 referes to the matched sub-expression part, and $it to the entire element.
#2
newLISP in the real world / # question
July 26, 2012, 10:29:04 PM
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Postby winger » Mon Jul 23, 2012 8:50 am

(background-color "#fffc17")

this is a html function .



now i want :

(background-color #:fffc17)

or

(background-color #fffc17)



but broken:

(sym "ffffaaaa" (sym "#"))



winger

     

    Posts: 14

    Joined: Wed Mar 14, 2012 7:31 am



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Postby Lutz » Tue Jul 24, 2012 3:31 pm

The # character is used as a comment character in newLISP. All characters on the same line following it, are taken as comment.



This allows writing mixed shell/newLISP scripts. E.g. all newLISP shell scripts in UNIX start with #!/usr/bin/newlisp or #!/usr/bin/env newlisp



Code: Select all

    #!/usr/bin/newlisp



    # this is an example UNIX script

    # containing newLISP code



    (println "Hello world")



    (exit)
#3
newLISP newS /
April 06, 2009, 06:48:15 AM
No. We would see a LOT of spammers if that happened.



I think I've stopped this guy. But I'm leaving his posts up for the moment while I work on things.
#4
newLISP newS /
April 06, 2009, 05:57:50 AM
Veeeeery interesting. I didn't register this guy. I'm trying to figure out how he got in here.
#5
newLISP newS / Alltime High
December 19, 2003, 07:06:47 PM
I don't have statistics per subdirectory for this website. The phpBB software isn't very informative either:



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All I can say is that the server struggles mightily under the load. :-)



Ryon
#6
newLISP newS /
January 17, 2003, 08:08:53 AM
It was a visit to la dentista. The US healthcare system is totally out of control, so I've started going south of the border for as much "routine maintenance" as possible. They do good work, and use modern equipment and techniques. And, you can buy a lot of tamales with the money saved.



I walked in without an appointment, and 45 minutes later walked out with a new filling. 36 Bucks! "Eet was a very BIG filling, señor!"