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  • car and cdr in scheme is driving me crazy ...

    - by kristian Roger
    Hi Im facing a probem with the car and cdr functions for example: first I defined a list caled it x (define x (a (bc) d ( (ef) g ) )) so x now is equal to (a (bc) d ( (ef) g ) now for example I need to get the g from this list using only car and cdr (!! noshortcuts as caddr cddr !!) the correct answer is: (car(cdr(car(cdr(cdr(cdr x)))))) BUT how ? :-( I work according to the rule (the car gives the head of list and cdr gives the tail) and instead of getting the answer above I keep reaching wronge answers can any one help me in understanding this ... give me step or a way to solve it step by step thanx in advance Im really sick of scheme language.

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  • car and cdr in Scheme are driving me crazy ...

    - by kristian Roger
    Hi Im facing a problem with the car and cdr functions for example: first I defined a list called it x (define x (a (bc) d ( (ef) g ) )) so x now is equal to (a (bc) d ( (ef) g ) ) now for example I need to get the g from this list using only car and cdr (!! noshortcuts as caddr cddr !!) the correct answer is: (car(cdr(car(cdr(cdr(cdr x)))))) BUT how ? :-( I work according to the rules (the car gives the head of list and cdr gives the tail) and instead of getting the answer above I keep reaching wrong answers. Can any one help me in understanding this ... give me step or a way to solve it step by step Thanks in advance. I'm really sick of Scheme.

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  • Websites' color scheme generators - what to do with them in real life?

    - by Marco Demaio
    On the web there are plenty of color scheme/palette generator tools and color palettes galleries. All of these tools/gelleries show many 3 to 5 colors palette as final result. Some of these tools: http://kuler.adobe.com, http://www.colorexplorer.com I know my question might sound ridicolous to someone who is involved in web dedign, but I don't understand what to do with these color palette. I mean, if I have to create a website, how am I supposed to apply this color palette to the website. Which color goes as foreground text, which one as background, which one for the links, which one for the page titles and so on? What are these color palette generators useful for then?! Thanks!

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  • How I Can do web programming with Lisp or Scheme?

    - by Castro
    I usually write web apps in PHP, Ruby or Perl. I am starting the study of Scheme and I want to try some web project with this language. But I can't find what is the best environment for this. I am looking for the following features: A simple way of get the request parameters (something like: get-get #key, get-post #key, get-cookie #key). Mysql access. HTML Form generators, processing, validators, etc. Helpers for filter user input data (something like htmlentities, escape variables for put in queries, etc). FLOSS. And GNU/Linux friendly. So, thanks in advance to all replies.

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  • How do i pass a number from a list as a parameter in scheme?

    - by wyatt
    I need to take a number from a list and convert it to a number so that i can pass it as a parameter. im trying to make a 1-bit adder in scheme. i've written the code for the or gate and the xor gate and also the half adder and now im trying to combine them all to make a full adder. im not sure if im going about it the right way. any input will be appreciated thank you. (define or-gate (lambda (a b) (if (= a 1) 1 (if (= b 1) 1 0)))) (define xor-gate (lambda (a b) (if (= a b) 0 1))) (define ha (lambda (a b) (list (xor-gate a b)(and-gate a b)))) (define fa (lambda (a b cin) (or-gate (cdr(ha cin (car (ha a b))))(cdr(ha a b))))) the issue i get when i run the program is that the half adder (ha) function outputs a list as a value and that makes the values incompatible with my other procedures because they require numbers and not lists. i feel like there is a simple solution but i dont know it.

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  • How do I map a macro across a list in Scheme?

    - by josh
    I have a Scheme macro and a long list, and I'd like to map the macro across the list, just as if it were a function. How can I do that using R5RS? The macro accepts several arguments: (mac a b c d) The list has (define my-list ((a1 b1 c1 d1) (a2 b2 c2 d2) ... (an bn cn dn))) And I'd like to have this: (begin (mac a1 b1 c1 d2) (mac a2 b2 c2 d2) ... (mac an bn cn dn)) (By the way, as you can see I'd like to splice the list of arguments too)

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  • Is it possible to define XML scheme with node names specified via regular expressions?

    - by MartyIX
    Hello, I know it is probably a question against XML philosophy but still is it possible to define scheme for XML like this: <Root> <arbitrary-name-of-node> <Name></Name> <Position></Position> <!-- ... --> </arbitrary-name-of-node> <arbitrary-name-of-node> <Name></Name> <Position></Position> <!-- ... --> </arbitrary-name-of-node> </Root> where arbitrary-name-of-node matches regular expression [a-zA-Z0-9]? Thanks for an answer!

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  • Can't understand example using continuations

    - by Matt Fenwick
    I'm reading the r6rs Scheme report and am confused by the explanation of continuations (I find it to be too dense and lacking of examples for a beginner). What is this code doing and how does it evaluate to 4? Why does call/cc want an argument that's a function of one argument? How is call/cc's argument used? (+ 1 (call-with-current-continuation (lambda (escape) (+ 2 (escape 3))))) =? 4 This example is from section 1.11 - Continuations.

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  • How useful are Lisp macros?

    - by compman
    Common Lisp allows you to write macros that do whatever source transformation you want. Scheme gives you a hygienic pattern-matching system that lets you perform transformations as well. How useful are macros in practice? Paul Graham said in Beating the Averages that: The source code of the Viaweb editor was probably about 20-25% macros. What sorts of things do people actually end up doing with macros?

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  • My Latest Hare-Brained Scheme

    - by Liam McLennan
    I have not had a significant side project for a while but I have been working on a product idea. Its an analytics application that analyses twitter data and reports on market sentiment. The target market is companies who want to track trends in consumer sentiment. My idea is to teach the application to divide relevant tweets into ‘positive’ and ‘negative’ categories. If the input was the set of tweets featuring the word ‘telstra’ the application would find the following tweet:   and put it in the ‘negative’ category. Collecting data in this fashion facilitates the creation of graphs such as: which can then be correlated against events, such as a share offer or new product release. I may go ahead and build this, just because I am a programmer and it amuses me to do so. My concerns are: There  is no market for this tool There is a market, but I don’t understand it and have no way to reach it.

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  • Prefilling an SMS on Mobile Devices with the sms: Uri Scheme

    - by Rick Strahl
    Popping up the native SMS app from a mobile HTML Web page is a nice feature that allows you to pre-fill info into a text for sending by a user of your mobile site. The syntax is a bit tricky due to some device inconsistencies (and quite a bit of wrong/incomplete info on the Web), but it's definitely something that's fairly easy to do.In one of my Mobile HTML Web apps I need to share a current location via SMS. While browsing around a page I want to select a geo location, then share it by texting it to somebody. Basically I want to pre-fill an SMS message with some text, but no name or number, which instead will be filled in by the user.What worksThe syntax that seems to work fairly consistently except for iOS is this:sms:phonenumber?body=messageFor iOS instead of the ? use a ';' (because Apple is always right, standards be damned, right?):sms:phonenumber;body=messageand that works to pop up a new SMS message on the mobile device. I've only marginally tested this with a few devices: an iPhone running iOS 6, an iPad running iOS 7, Windows Phone 8 and a Nexus S in the Android Emulator. All four devices managed to pop up the SMS with the data prefilled.You can use this in a link:<a href="sms:1-111-1111;body=I made it!">Send location via SMS</a>or you can set it on the window.location in JavaScript:window.location ="sms:1-111-1111;body=" + encodeURIComponent("I made it!");to make the window pop up directly from code. Notice that the content should be URL encoded - HTML links automatically encode, but when you assign the URL directly in code the text value should be encoded.Body onlyI suspect in most applications you won't know who to text, so you only want to fill the text body, not the number. That works as you'd expect by just leaving out the number - here's what the URLs look like in that case:sms:?body=messageFor iOS same thing except with the ;sms:;body=messageHere's an example of the code I use to set up the SMS:var ua = navigator.userAgent.toLowerCase(); var url; if (ua.indexOf("iphone") > -1 || ua.indexOf("ipad") > -1) url = "sms:;body=" + encodeURIComponent("I'm at " + mapUrl + " @ " + pos.Address); else url = "sms:?body=" + encodeURIComponent("I'm at " + mapUrl + " @ " + pos.Address); location.href = url;and that also works for all the devices mentioned above.It's pretty cool that URL schemes exist to access device functionality and the SMS one will come in pretty handy for a number of things. Now if only all of the URI schemes were a bit more consistent (damn you Apple!) across devices...© Rick Strahl, West Wind Technologies, 2005-2013Posted in IOS  JavaScript  HTML5   Tweet !function(d,s,id){var js,fjs=d.getElementsByTagName(s)[0];if(!d.getElementById(id)){js=d.createElement(s);js.id=id;js.src="//platform.twitter.com/widgets.js";fjs.parentNode.insertBefore(js,fjs);}}(document,"script","twitter-wjs"); (function() { var po = document.createElement('script'); po.type = 'text/javascript'; po.async = true; po.src = 'https://apis.google.com/js/plusone.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(po, s); })();

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  • Color scheme for programmers

    - by seler
    Recently I've discovered Solarized. It's supposed to reduce eye-fatigue and after using it for a while i must say it's true. When I switched back to my old colors they were damn to bright. I don't really like the colors in Solarized theme but I'm astonished by the effect it has on my eyes. I'm wondering if there are other themes designed with such a precision for wide range of IDEs (and even terminal colors!). Another example is Zenburn

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  • Scheme of work contract

    - by Tommy
    I'm in the process of setting up a (one man) company and got to a item on my list "contracts and insurance". I will primary be offering custom software development but may also offer some "open source solutions", install, configure / manage e.t.c. I'm not sure how to approach a contract with a potential customer. I want to be flexible and offer the customer rights over the product (when not using open source of course) but I obviously want / need to be able to reuse code, already written and any future work. Is this possible or is it just something that people do but strictly they shouldn't? Is there a standard freelancing / contacting developer agreement? Going to a lawyer I'm sure is an answer but a very expensive one! If not do you end up with a fresh contract with each job / client and lots of trips to solicitors?

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  • Permissions scheme not working

    - by ReaZem
    I am currently building a home server and I am trying to give minimal permissions to every service. I am new to permissions management and this is an awesome learning experience for me :). drwxr----- 7 reazem enter-home 4096 Sep 9 21:43 reazem drwxrws--- 3 reazem minidlna 4096 Sep 9 21:36 media reazem is my home folder and media is my media folder, it is situated directly inside my home. The minidlna user is part of the following groups : minidlna, enter-home. I get the following error: Media directory not accessible! [/home/reazem/media] I was hoping that because the minidlna user is part of the enter-home group, it could get inside the home folder, and then inside the media folder because it is in the minidlna group. Where is my mistake? Edit: I found out that chmod g+x /home/reazem solved the problem, but why? Why would you need the execute permission to get inside another directory? Thank you!

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  • Is LISP still useful in, and which version is most used in todays world ?

    - by shan23
    I try to teach myself a new programming language in regular intervals of time. Recently, I've read how Lisp and its dialects are at the complete opposite end of the spectrum from languages like C/C++, which made me curious enough to know more about it. However, two things are unclear to me, and I'm looking for guidance on them : Is LISP still practiced/used in todays world, or is it a legacy language like FORTRAN/COBOL ? I mean, apart from maintaining existing code, is it used on new projects at all ? What is the most widely used dialect ? I came across Scheme and Common Lisp as the 2 most prevalent dialects, and wanted your opinion as to which is the most favored/useful one to learn - and would be immensely gratified if you can suggest any resources for a rank beginner to start from. While eager to learn a language which is fundamentally different from the procedural languages I'm used to, I don't want to invest undue effort in something if its totally obsolete - I'd still learn it if it was professionally "dead", but only with an academic perspective...

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  • Too much to learn, so little time

    - by Phobia
    Okay, so I'm a java developer (or at least I think I am),and also a student at the same time I want to get a job when I graduate,I'll be graduating in a year or so (hopefully) (Note: my major has nothing to do with programming) Now, I'm between a rock and a hard place I also want to nail the foundations to become a good software developer. I want to be able to write programs that solve problems,not just glue code The software market in my country for java developers is just a few developers working with Java EE (struts,spring,hibernate....etc) I'm currently learning C++ with this book. I've also watched most of the 1st lecture of this course and I understood pretty much everything I watched To sum it up, I have three options Learn Java EE Learn C++ Learn Scheme Which is better for me at this point?

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  • What is a dotted pair's analogy in other Lisp implementations?

    - by octopusgrabbus
    What is Scheme's dotted pair construct analogous to in other Lisp implementations? I can make a vector or list quite easily, and understand those in Clojure, even though the syntax is a little different, like Clojure's vectors use square brackets []. However, seeing a dotted pair for the first time threw me. It almost looks like it is an implementation of of map. I'm not looking for a discussion, but more for use or the dotted pair equivalent in other Lisp dialects, like Clojure, or even Python. Thanks.

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  • Learning C, Lisp, and UNIX from Ground Up

    - by hunterc
    A friend and I are trying to learn traditional programming from the ground up. We both do web stuff primarily but want to expand to more system related things. We have found a ton of resources but looking for a road map of sorts. We are planning on using SICP to learn Lisp(scheme). Don't really know where to from there. As for C, we figured we'd start with K&R, then do OOC, and sprinkle in Operating Systems Design and Implementation and kind of learn UNIX as we go. I'd really appreciate suggestions on filling in the gaps, reordering things, or just advice in general.

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  • Getting svn: E170000: Unrecognized URL scheme for my custom Svn Gradle plugin

    - by Ip Doh
    I wrote a custom gradle plugin using groovy to do basic svn tasks like, Checkout, Clean, Tag etc. The groovy class calls the svn command line client to do these operations, It works fine when i run it on my windows system but the same plugin gives the following error when i run it on a linux system (Centos). svn: E170000: Unrecognized URL scheme for '%22https://source.mycompany.net/svn/MyProject/trunk%22' Am able to make the same calls to the command line client through the command prompt or shell script without any issues. So what is the difference with Here is my code sample String command =String.format("svn co -r %d --non-interactive --trust-server-cert -- username %s --password %s --depth infinity \"%s\" \"%s\"", getRevision(), getUserName(), getUserPassword(), getSrcUrl(), getDir()); Process svnProcess = Runtime.getRuntime().exec(command); BufferedReader stdInput = new BufferedReader(new InputStreamReader(svnProcess.getInputStream())); BufferedReader stdError = new BufferedReader(new InputStreamReader(svnProcess.getErrorStream())); String statusOutputLine ="" while ((statusOutputLine = stdInput.readLine()) != null) { logger.quiet(" " + statusOutputLine); } while (( statusOutputLine = stdError.readLine()) != null) { logger.error(statusOutputLine) throw new Exception(statusOutputLine) } logger.quiet("Successfully Checked out the work space") i do have neon installed on the system -bash-4.1$ svn --version svn, version 1.6.11 (r934486) compiled Jun 25 2011, 11:30:15 Copyright (C) 2000-2009 CollabNet. Subversion is open source software, see http://subversion.tigris.org/ This product includes software developed by CollabNet (http://www.Collab.Net/). The following repository access (RA) modules are available: ra_neon : Module for accessing a repository via WebDAV protocol using Neon. handles 'http' scheme handles 'https' scheme ra_svn : Module for accessing a repository using the svn network protocol. with Cyrus SASL authentication handles 'svn' scheme ra_local : Module for accessing a repository on local disk. handles 'file' scheme

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  • Scheme. Tail recursive ?

    - by n00b
    Hi guys, any tail-recursive version for the below mentioned pseudocode ? Thanks ! (define (min list) (cond ((null? list '()) ((null? (cdr list)) (car list)) (#t (let ((a (car list)) (b (min (cdr list))) ) (if (< b a) b a) ) ) ) )

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