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  • Custom language - FOR loop in a clojure interpeter?

    - by Mark
    I have a basic interpreter in clojure. Now i need to implement for (initialisation; finish-test; loop-update) { statements } Implement a similar for-loop for the interpreted language. The pattern will be: (for variable-declarations end-test loop-update do statement) The variable-declarations will set up initial values for variables.The end-test returns a boolean, and the loop will end if end-test returns false. The statement is interpreted followed by the loop-update for each pass of the loop. Examples of use are: (run ’(for ((i 0)) (< i 10) (set i (+ 1 i)) do (println i))) (run ’(for ((i 0) (j 0)) (< i 10) (seq (set i (+ 1 i)) (set j (+ j (* 2 i)))) do (println j))) inside my interpreter. I will attach my interpreter code I got so far. Any help is appreciated. Interpreter (declare interpret make-env) ;; needed as language terms call out to 'interpret' (def do-trace false) ;; change to 'true' to show calls to 'interpret' ;; simple utilities (def third ; return third item in a list (fn [a-list] (second (rest a-list)))) (def fourth ; return fourth item in a list (fn [a-list] (third (rest a-list)))) (def run ; make it easy to test the interpreter (fn [e] (println "Processing: " e) (println "=> " (interpret e (make-env))))) ;; for the environment (def make-env (fn [] '())) (def add-var (fn [env var val] (cons (list var val) env))) (def lookup-var (fn [env var] (cond (empty? env) 'error (= (first (first env)) var) (second (first env)) :else (lookup-var (rest env) var)))) ;; for terms in language ;; -- define numbers (def is-number? (fn [expn] (number? expn))) (def interpret-number (fn [expn env] expn)) ;; -- define symbols (def is-symbol? (fn [expn] (symbol? expn))) (def interpret-symbol (fn [expn env] (lookup-var env expn))) ;; -- define boolean (def is-boolean? (fn [expn] (or (= expn 'true) (= expn 'false)))) (def interpret-boolean (fn [expn env] expn)) ;; -- define functions (def is-function? (fn [expn] (and (list? expn) (= 3 (count expn)) (= 'lambda (first expn))))) (def interpret-function ; keep function definitions as they are written (fn [expn env] expn)) ;; -- define addition (def is-plus? (fn [expn] (and (list? expn) (= 3 (count expn)) (= '+ (first expn))))) (def interpret-plus (fn [expn env] (+ (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define subtraction (def is-minus? (fn [expn] (and (list? expn) (= 3 (count expn)) (= '- (first expn))))) (def interpret-minus (fn [expn env] (- (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define multiplication (def is-times? (fn [expn] (and (list? expn) (= 3 (count expn)) (= '* (first expn))))) (def interpret-times (fn [expn env] (* (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define division (def is-divides? (fn [expn] (and (list? expn) (= 3 (count expn)) (= '/ (first expn))))) (def interpret-divides (fn [expn env] (/ (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define equals test (def is-equals? (fn [expn] (and (list? expn) (= 3 (count expn)) (= '= (first expn))))) (def interpret-equals (fn [expn env] (= (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define greater-than test (def is-greater-than? (fn [expn] (and (list? expn) (= 3 (count expn)) (= '> (first expn))))) (def interpret-greater-than (fn [expn env] (> (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define not (def is-not? (fn [expn] (and (list? expn) (= 2 (count expn)) (= 'not (first expn))))) (def interpret-not (fn [expn env] (not (interpret (second expn) env)))) ;; -- define or (def is-or? (fn [expn] (and (list? expn) (= 3 (count expn)) (= 'or (first expn))))) (def interpret-or (fn [expn env] (or (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define and (def is-and? (fn [expn] (and (list? expn) (= 3 (count expn)) (= 'and (first expn))))) (def interpret-and (fn [expn env] (and (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define print (def is-print? (fn [expn] (and (list? expn) (= 2 (count expn)) (= 'println (first expn))))) (def interpret-print (fn [expn env] (println (interpret (second expn) env)))) ;; -- define with (def is-with? (fn [expn] (and (list? expn) (= 3 (count expn)) (= 'with (first expn))))) (def interpret-with (fn [expn env] (interpret (third expn) (add-var env (first (second expn)) (interpret (second (second expn)) env))))) ;; -- define if (def is-if? (fn [expn] (and (list? expn) (= 4 (count expn)) (= 'if (first expn))))) (def interpret-if (fn [expn env] (cond (interpret (second expn) env) (interpret (third expn) env) :else (interpret (fourth expn) env)))) ;; -- define function-application (def is-function-application? (fn [expn env] (and (list? expn) (= 2 (count expn)) (is-function? (interpret (first expn) env))))) (def interpret-function-application (fn [expn env] (let [function (interpret (first expn) env)] (interpret (third function) (add-var env (first (second function)) (interpret (second expn) env)))))) ;; the interpreter itself (def interpret (fn [expn env] (cond do-trace (println "Interpret is processing: " expn)) (cond ; basic values (is-number? expn) (interpret-number expn env) (is-symbol? expn) (interpret-symbol expn env) (is-boolean? expn) (interpret-boolean expn env) (is-function? expn) (interpret-function expn env) ; built-in functions (is-plus? expn) (interpret-plus expn env) (is-minus? expn) (interpret-minus expn env) (is-times? expn) (interpret-times expn env) (is-divides? expn) (interpret-divides expn env) (is-equals? expn) (interpret-equals expn env) (is-greater-than? expn) (interpret-greater-than expn env) (is-not? expn) (interpret-not expn env) (is-or? expn) (interpret-or expn env) (is-and? expn) (interpret-and expn env) (is-print? expn) (interpret-print expn env) ; special syntax (is-with? expn) (interpret-with expn env) (is-if? expn) (interpret-if expn env) ; functions (is-function-application? expn env) (interpret-function-application expn env) :else 'error))) ;; tests of using environment (println "Environment tests:") (println (add-var (make-env) 'x 1)) (println (add-var (add-var (add-var (make-env) 'x 1) 'y 2) 'x 3)) (println (lookup-var '() 'x)) (println (lookup-var '((x 1)) 'x)) (println (lookup-var '((x 1) (y 2)) 'x)) (println (lookup-var '((x 1) (y 2)) 'y)) (println (lookup-var '((x 3) (y 2) (x 1)) 'x)) ;; examples of using interpreter (println "Interpreter examples:") (run '1) (run '2) (run '(+ 1 2)) (run '(/ (* (+ 4 5) (- 2 4)) 2)) (run '(with (x 1) x)) (run '(with (x 1) (with (y 2) (+ x y)))) (run '(with (x (+ 2 4)) x)) (run 'false) (run '(not false)) (run '(with (x true) (with (y false) (or x y)))) (run '(or (= 3 4) (> 4 3))) (run '(with (x 1) (if (= x 1) 2 3))) (run '(with (x 2) (if (= x 1) 2 3))) (run '((lambda (n) (* 2 n)) 4)) (run '(with (double (lambda (n) (* 2 n))) (double 4))) (run '(with (sum-to (lambda (n) (if (= n 0) 0 (+ n (sum-to (- n 1)))))) (sum-to 100))) (run '(with (x 1) (with (f (lambda (n) (+ n x))) (with (x 2) (println (f 3))))))

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  • wildcards to use in codeigniter routing?

    - by ajsie
    in codeigniter you can use wildcard to reroute. i never heard the word wildcards before. is this a set of rules you can use like regexp? cause in codeigniter documentation they just gave some examples eg. $route['product/(:num)'] = "catalog/product_lookup_by_id/$1"; is there a list/reference with all the available wildcard expressions you can use?

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  • jQuery table filter with text, checkboxes, selects

    - by Jeffrey
    Need to filter a table from outside of the table, with a text search, checkboxes, and selects. PicNet Table Filter for jQuery works for both searching and using checkboxes outside of the table... though I can't find any examples of how to get a select box to work. Anyone know? *I might be getting too specific here, but thought I'd at least inquire. I'm also open to possibilities other than PicNet.

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  • Displaying multidimensional data in WPF

    - by KrisTrip
    What is the best way to display multidimensional data in WPF? I want to use databinding and I won't know the size/shape of the data until runtime. I was thinking some sort of grid but I don't know how to dynamically bind to the data and have it figure out the number of rows and columns. Suggestions and examples please?

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  • DNS issue on Fedora 12? wget wordpress.org fails where wget www.google.com works

    - by Tom Auger
    I'm administering a Fedora 12 box, but am quite new to networking specifics. Recently one of our WordPress apps hosted on our server has stopped being able to perform its auto-update or auto-download of plugins. Investigating further, I have tried the following: $ wget wordpress.org --2010-12-17 11:26:50-- http://wordpress.org/ Resolving wordpress.org... failed: Temporary failure in name resolution. wget: unable to resolve host address âwordpress.orgâ Whereas: $ wget www.google.com --2010-12-17 11:27:26-- http://www.google.com/ Resolving www.google.com... 74.125.226.82, 74.125.226.84, 74.125.226.80, ... Connecting to www.google.com|74.125.226.82|:80... connected. HTTP request sent, awaiting response... 302 Found Location: http://www.google.ca/ [following] --2010-12-17 11:27:26-- http://www.google.ca/ Resolving www.google.ca... 173.194.32.104 Connecting to www.google.ca|173.194.32.104|:80... connected. HTTP request sent, awaiting response... 200 OK Length: unspecified [text/html] Saving to: âindex.html.4â [ <=> ] 9,079 --.-K/s in 0.02s 2010-12-17 11:27:26 (462 KB/s) - âindex.html.4â Interestingly: $ ping wordpress.org PING wordpress.org (72.233.56.138) 56(84) bytes of data. 64 bytes from wordpress.org (72.233.56.138): icmp_seq=1 ttl=50 time=81.5 ms 64 bytes from wordpress.org (72.233.56.138): icmp_seq=2 ttl=50 time=67.3 ms ^C --- wordpress.org ping statistics --- 2 packets transmitted, 2 received, 0% packet loss, time 1783ms rtt min/avg/max/mdev = 67.361/74.448/81.536/7.092 ms and $ nslookup wordpress.org Server: 192.168.2.1 Address: 192.168.2.1#53 Non-authoritative answer: Name: wordpress.org Address: 72.233.56.138 Name: wordpress.org Address: 72.233.56.139 nscd has been stopped and flushed. iptables appear to be clean. At this point I have exhausted my limited abilities to diagnose the issue. Can anyone suggest a resolution path?

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  • Forward mDns from one subnet to another?

    - by user37278
    Is there an ipfw rule that can easily forward mDns packets from one subnet to another? I have a Snow Leopard Server machine serving as the gateway between the two subnets and would like for machines in each subnet to see the services available in the other subnet. The gateway machine is already confirmed as configured correctly such that packets route correctly between the two subnets (ping works, traceroute shows the subnet hop, etc). My problem in designing a ipfw rule is that I don't know how to instruct that I would like multicast packets addressed to 224.0.0.251:5353 on en0 to be addressed to the same ip/port but on fw0 (the other interface). I attempted a rule such as fwd 192.168.10.1 log udp from 192.168.1.0/24 to 224.0.0.251 recv en1 to force the packet to hop over to the other interface (from en1 to fw0), but no dice. The ipfw log shows that the rule is being triggered by packets, but tcpdump isn't showing any packets on the other interface. Also, the only other firewall rules in place are the divert port 8668 and rule #65535 "allow any to any". Any suggestions? Thanks.

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  • What is a RECURSIVE Function in PHP?

    - by Imran
    Can anyone please explain a recursive function to me in PHP (without using Fibonacci) in layman language and using examples? i was looking at an example but the Fibonacci totally lost me! Thank you in advance ;-) Also how often do you use them in web development?

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  • CentOS 6.3 Virtual under OpenVZ cannot ping, host lookups, outbound connections while postfix running

    - by Paul Cravey
    My best theory is that some kernel limit is being hit preventing outbound connections. We have tried basically everything from tcpdumps to provisioning an entirely new virtual server (we do not have this problem on any other virtuals), however the problem somehow carried over, even with new postfix build (working). Emails work, and outbound connections work, so long as postfix does not have too much going on. /proc/user_beancounters shows no limits being hit (show below). Nevertheless, pings fail even to IP addresses. TCP stack appears healthy. Load is low. No iowait. Flushed iptables already. Has anyone experienced anything like this? uid resource held maxheld barrier limit failcnt 3: kmemsize 166216365 170262528 9223372036854775807 9223372036854775807 0 lockedpages 0 0 9223372036854775807 9223372036854775807 0 privvmpages 285727 351885 9223372036854775807 9223372036854775807 0 shmpages 16933 17605 9223372036854775807 9223372036854775807 0 dummy 0 0 0 0 0 numproc 150 303 9223372036854775807 9223372036854775807 0 physpages 314156 326191 0 1280000 0 vmguarpages 0 0 9223372036854775807 9223372036854775807 0 oomguarpages 165355 165355 9223372036854775807 9223372036854775807 0 numtcpsock 89 172 9223372036854775807 9223372036854775807 0 numflock 22 76 9223372036854775807 9223372036854775807 0 numpty 1 2 9223372036854775807 9223372036854775807 0 numsiginfo 0 75 9223372036854775807 9223372036854775807 0 tcpsndbuf 2733472 4371752 9223372036854775807 9223372036854775807 0 tcprcvbuf 1798336 5427296 9223372036854775807 9223372036854775807 0 othersockbuf 491120 1000760 9223372036854775807 9223372036854775807 0 dgramrcvbuf 0 238728 9223372036854775807 9223372036854775807 0 numothersock 361 505 9223372036854775807 9223372036854775807 0 dcachesize 135941831 136114679 9223372036854775807 9223372036854775807 0 numfile 2905 4990 9223372036854775807 9223372036854775807 0 dummy 0 0 0 0 0 dummy 0 0 0 0 0 dummy 0 0 0 0 0 numiptent 8 9 9223372036854775807 9223372036854775807 0 [root@bni /]# ping 4.2.2.1 PING 4.2.2.1 (4.2.2.1) 56(84) bytes of data. --- 4.2.2.1 ping statistics --- 9 packets transmitted, 0 received, 100% packet loss, time 8493ms [root@bni /]# service postfix stop [root@bni /]# ping 4.2.2.1 PING 4.2.2.1 (4.2.2.1) 56(84) bytes of data. 64 bytes from 4.2.2.1: icmp_seq=1 ttl=53 time=8.63 ms 64 bytes from 4.2.2.1: icmp_seq=2 ttl=53 time=8.62 ms 64 bytes from 4.2.2.1: icmp_seq=3 ttl=53 time=8.63 ms 64 bytes from 4.2.2.1: icmp_seq=4 ttl=53 time=8.66 ms Outbound connections of all sorts fail when postfix is running.

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  • Python sock.listen(...)

    - by Ian
    All the examples I've seen of sock.listen(5) in the python documentation suggest I should set the max backlog number to be 5. This is causing a problem for my app since I'm expecting some very high volume (many concurrent connections). I set it to 200 and haven't seen any problems on my system, but was wondering how high I can set it before it causes problems.. Anyone know?

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  • software for sorting algorithms animation

    - by Dinesh
    I am planning on working on an interactive application that graphically animates the various sorting algorithms in action. Most of the examples of this kind on the web seems to be using java applets. I was wondering what other software/tools would be well suited to develop an application like this. It may or may not be web-based. Any help would be greatly appreciated. Thanks Dinesh

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  • drawing hierarchical tree with orthogonal lines

    - by user267530
    Hi I need to work on drawing a hierarchical tree structure with orthogonal lines(straight rectangular connecting lines) between root and children ( like the following: http://lab.kapit.fr/display/visualizationlayouts/Hierarchical+Tree+layout ). I want to know if there are any open source examples of the algorithm of drawing trees like that so that I can implement the same algorithm in actionscript. Thanks Palash

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  • Get length of bits used in int

    - by sigvardsen
    If you have the binary number 10110 how can I get it to return 11111? e.g a new binary number that sets all bits to 1 after the first 1, there are some likewise examples listed below: 101 should return 111 (3 bit length) 011 should return 11 (2 bit length) 11100 should be return 11111 (5 bit length) 101010101 should return 111111111 (9 bit length) How can this be obtained the easiest way in Java? I could come up with some methods but they are not very "pretty".

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  • Fowler Analysis Patterns lately?

    - by Berryl
    As much as I've always loved this one is how much I always wished there were more meaty examples of how to apply some of the concepts available. Is anyone aware of anything out there worth looking at that attempts to that? Cheers, Berryl

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  • CouchDB Find One not working

    - by Andrew
    I am a couchDB newbie and am doing the examples in the O'Reilly CouchDB guide. I have a problem using a view to retrieve a document by key: curl http://127.0.0.1:5984/basic/_design/example/_view/by_date?key="2009/01/15 15:52:20" gives the reply: curl: (52) Empty reply from server but just retrieving all rows: curl http://127.0.0.1:5984/basic/_design/example/_view/by_date gives me 3 rows including the specific row I am looking for: {"id":"hello-world","key":"2009/01/15 15:52:20","value":"Hello World"} why doesn't the key query work? I am using CouchDB version 0.10.0 on Ubuntu 9.10

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  • What is the replacement of the floppy

    - by alexanderpas
    While CD (and to an lesser extend DVD) disks have reached the price-point of the floppy, they have one significant downside, it is WORM (Write-Once Read-Many) media, allowing it to be used only one single time, and you need to be explicit in writing the data to the actual media (you need to burn it.) While CD-RW solves the "use only once" problem, it is still EWORM (Erasable Write-Once Read-Many) media, which still means you need to be explicit in writing the data to the actual media (you still need to burn it.), and also, you still need to be very explicit in erasing it. (simple delete is not possible.) Okay, we can use a CD-RW in Packet Writing mode, however the downside to that, is that this mode is not very universal, and also, not the native mode of the media. Now, while USB-sticks and SD-cards may not have the poblems of the CD, they have a whole other kind of problem: their PRICE! USB-sticks and SD cards are generally 10 to 100 times as expensive as diskettes per piece. SD-cards, in addition have an added problem, because they need a reader to operate. While it is a very standard thing, it is not default equipment on the computer like the CD drive or USB port (or historically the diskette drive). You wouldn't give out an USB stick or SD card with a 100 kB text file, not caring weither you would get it back or not. So, to recap: CD & DVD are basically WORM media. SD cards and USB sticks are relatively expensive. SD cards also needs special readers. Diskettes have a very low data-rate Diskettes have a very low storage capacity. Now, is there a media out there that solves all these problems, or is there a way to get (very) small USB sticks or SD cards for a very low price (as they're the closest thing to diskette).

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  • Move options between multiple dropdown lists

    - by Martha
    We currently have a form with the standard multi-select functionality of "here are the available options, here are the selected options, here are some buttons to move stuff back and forth." However, the client now wants the ability to not just select certain items, but to also categorize them. For example, given a list of books, they want to not just select the ones they own, but also the ones they've read, the ones they would like to read, and the ones they've heard about. (All examples fictional.) Thankfully, a selected item can only be in one category at a time. I can find many examples of moving items between listboxes, but not a single one for moving items between multiple listboxes. To add to the complication, the form needs to have two sets of list+categories, e.g. a list of movies that need to be categorized in addition to the aforementioned books. An additional problem is that sorting between lists is all well and good in the javascript-enabled world, but I can't really think of a good fallback interface for, say, mobile browsers. Maybe a pseudo-listbox with radio buttons next to each item? The master list of items will in general be very long - over 100 items, certainly, possibly many more. Any given category will most likely contain one or two selected items, but the possibility exists for a category to have dozens of selected items, or zero selected items. As far as OS and stuff, the site is in classic asp (quit snickering!), the server-side code is VBScript, and so far we've avoided the various Javascript libraries by the simple expedient of almost never using client-side scripting. This one form for this one client is currently the big exception. Give 'em an inch and they want a mile... Oh, and I have to add: I suck at Javascript, or really at any C-descendant language. Curly braces give me hives. I'd really, really like something I can just copy & paste into my page, maybe tweak some variable names, and never look at it again. A girl can dream, can't she? :)

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  • What's with "foo" and "bar" [closed]

    - by Matt S.
    Possible Duplicates: When foo and bar is not enough Code examples Foo Bar I've always wondered, why is there always "foo" and "bar" named as variables in most tutorials I've seen. Where did it come from? Why do we call them "foo" and "bar" why not something else?

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  • Programmatically add IP(s) or domain(s) to Relay Restrictions in SMTP Virtual Server on IIS 6

    - by RJ
    I have been given a task to create an admin page to programmatically add IPs or domains to a SMTP Relay Restrictions using C#. I spent some time researching this since yesterday and finally traced this down to a few posts on several website that use the System.DirectoryServices.DirectoryEntr class. Using the examples I found, I can add or deny IPs or domains under Connection control but not Relay Restrictions. What would be the commands in C# to add IPs to the Relay Restrictions? Below is a pic of the GUI in IIS for reference.-

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