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• How to assign a numbering scheme to TreeNodes based on position

  - by TChristian

  I have a TreeView control in a Windows Forms application that is displaying my own subclass of TreeNode. I need to display a number along with each node's text indicating its position in the tree, like 1 for the root, 1.1 for its first child, 1.2 for its second child, etc. I'm using C# with .NET 2.0 The best that I can come up with is, after the tree is built, go to each node, recursively find the parent and append the parent's sibling number to the front of the node's text until you reach the root.

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• What's the sql scheme for supporting Tags system?

  - by Tom

  Hi, i've coded a tiny forum software in php where people posts threads, and i want to support tags. How many SQL tables should i make for this ? and briefly how the tags system will work? Thanks

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• parsing a list and producing a structure of that

  - by qzar

  ;; structure representing homework points ;; nr: number - the number of the homework ;; points: number - the number of points reached (define-struct homework (nr points)) ;; parse-homework: (list of number pairs) -> (list of homework) ;; The procedure takes a list of number pairs and produces a list of homework structures ;; Example: (parse-homework (list (list 1 6) (list 2 7) (list 3 0))) should produce (list (make-homework 1 6) (make-homework 2 7) (make-homework 3 0)) (define (parse-homework homework-entries) (if (and (= (length (first homework-entries) 2))(= (length (parse-homework (rest homework-entries)) 2))) (make-homework (first homework-entries) (parse-homework (rest homework-entries))) (error 'Non-valid-input "entered list is not of length two")) ) (parse-homework (list (list 1 6) (list 2 7) (list 3 0))) This code produces the error length: expects 1 argument, given 2: (list 1 6) 2 I really appreciate every explanation that you can give me to get in in this scheme-stuff... Thank you very much

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• Rewriting UNIX cal(1)

  - by dharmatech

  Hello, Today I was testing out SRFI 19 and wrote a simple version of the UNIX cal(1) command. Here's a version in R6RS Scheme which runs in Ikarus and Ypsilon. A few example runs. Schemers: How would you write it? Use your favorite implementation. Ruby and Python: I'm guessing that y'all have elegant date and time libraries. I'm sure you can put the Schemers to shame. ;-) Let's see what ya got. I'd also like to see Haskell and golfed versions. Is there a Stack Overflow tag for re-implementations of UNIX commands? :-) Ed

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• What does this xkcd code do?

  - by cobbal

  On the xkcd site today, the following appeared as a joke in a <script language="scheme"> tag so what does the following code do / represent? (define (eval exp env) (cond ((self-evaluating? exp) exp) ((variable? exp) (lookup-variable-value exp env)) ((quoted? exp) (text-of-quotation exp)) ((assignment? exp) (eval-assignment exp env)) ((definition? exp) (eval-definition exp env)) ((if? exp) (eval-if exp env)) ((lambda? exp) (make-procedure (lambda-parameters exp) (lambda-body exp) env)) ((begin? exp) (eval-sequence (begin-actions exp) env)) ((cond? exp) (eval (cond->if exp) env)) ((application? exp) (apply (eval (operator exp) env) (list-of-values (operands exp) env))) (else (error "Common Lisp or Netscape Navigator 4.0+ Required" exp))))

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• Too many argumants for function

  - by Stas Kurilin

  I'm starting learning Lisp with Java background. In SICP's exercise there is many tasks where students should create abstract functions with many parameters, like (define (filtered-accumulate combiner null-value term a next b filter)...) in exercise 3.11. In Java (language with safe, static typing discipline) - method with more than 4 arguments usually smells, but in Lisp/Scheme it doesnt, does it? I'm wandering how many arguments do you use in you functions? If you use it in production, do you make such many layers?

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• How are vector patterns used in syntax-rules?

  - by Jay

  Hi, I have been writing Common Lisp macros, so Scheme's R5Rs macros are a bit unnatural to me. I think I got the idea, except that I don't understand how one would use vector patterns in syntax-rules: (define-syntax mac (syntax-rules () ((mac #(a b c d)) (let () (display a) (newline) (display d) (newline))))) (expand '(mac #(1 2 3 4))) ;; Chicken's expand-full extension shows macroexpansion => (let746 () (display747 1) (newline748) (display747 4) (newline748)) I don't see how I'd use a macro that requires its arguments to be written as a vector: (mac #(1 2 3 4)) => 1 4 Is there some kind of technique that uses those patterns? Thank you!

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• Why exactly is eval evil?

  - by Jay

  I know that Lisp and Scheme programmers usually say that eval should be avoided unless strictly necessary. I´ve seen the same recommendation for several programming languages, but I´ve not yet seen a list of clear arguments against the use of eval. Where can I find an account of the potential problems of using eval? For example, I know the problems of GOTO in procedural programming (makes programs unreadable and hard to maintain, makes security problems hard to find, etc), but I´ve never seen the arguments against eval. Interestingly, the same arguments against GOTO should be valid against continuations, but I see that Shemers, for example, won´t say that continuations are "evil" -- you should just be careful when using them. They´re much more likely to frown upon code using eval than upon code using continuations (as far as I can see -- I could be wrong).

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• How to have a dynamic theme color in WPF

  - by Ingó Vals

  In WPF I have a few resource dictionaries and in them styles for my panels and controls in my app. I'm reusing the same colors again and again. I actually have 5 colors and they give my app a good color-scheme. However if I wan't to change the theme I have to go into the RD's and change each and every color there. I would like to somewhere have the colors set but don't know how or where. I tried to put a color tag in one RD but as soon as I referenced it in the same RD Visual Studio crashed. Also the best solution would be that I could have the color as a dynamic setting in the app itself so users could even change it themselves.

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• Newbie programmer looking for a fun, small project (pref. C++/Python)

  - by Francisco P.

  Hello everyone, I have some experience in Scheme and C++ (read: a semester of each) I know the very basics of Python (used it for physics simulations with the Visual Python module). Can you recommend me some fun and small (i.e. don't take much time) projects on either Python or C++? I have no real preferences, just that it is fun :P Thanks for your time! PS: I've tried projecteuler and python challenge. Euler is good, but more about math than coding, and py challenge just didn't work for me.

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• Experiences teaching or learning map/reduce/etc before recursion?

  - by Jay

  As far as I can see, the usual (and best in my opinion) order for teaching iterting constructs in functional programming with Scheme is to first teach recursion and maybe later get into things like map, reduce and all SRFI-1 procedures. This is probably, I guess, because with recursion the student has everything that's necessary for iterating (and even re-write all of SRFI-1 if he/she wants to do so). Now I was wondering if the opposite approach has ever been tried: use several procedures from SRFI-1 and only when they are not enough (for example, to approximate a function) use recursion. My guess is that the result would not be good, but I'd like to know about any past experiences with this approach.

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• Definition of "lisp form"?

  - by josh

  Hi, What exactly the definition of a "Lisp form"? As far as I know, it's "either an atom or a list that has a symbol as its first element". But then, this (in Scheme) would not be a form: ((lambda () 42)) ;; The answer to Life, the Universe and Everything. Because the first element of the list is itself another list. And after it's evaluated it will be a procedure (not a symbol). I can find several different websites and tutorials talking about Lisp forms, but none which gives a complete and detailed definition. Where can I find one?

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• Writing lambda functions in Scala

  - by user2433237

  I'm aware that you can write anonymous functions in Scala but I'm having trouble trying to convert a piece of code from Scheme. Could anyone help me convert this to Scala? (define apply-env (lambda (env search-sym) (cases environment env (empty-env () (eopl:error 'apply-env "No binding for ~s" search-sym)) (extend-env (var val saved-env) (if (eqv? search-sym var) val (apply-env saved-env search-sym))) (extend-env-rec (p-name b-var p-body saved-env) (if (eqv? search-sym p-name) (proc-val (procedure b-var p-body env)) (apply-env saved-env search-sym)))))) Thanks in advance

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• Extra line breaks inserted in MrEd text%

  - by Jesse Millikan

  In a DrScheme project, I'm using a MrEd editor-canvas% with text% and inserting a string from a literal in a Scheme file. This results in an extra blank line in the editor for each line of text I'm trying to insert. Is this a Windows vs. Unix linebreak problem? I can't find anything about text% treats line breaks in the documentation. ; Inside a class definition: (define/public (edit-pattern p j b d h) (send input-beat set-value (number->string b)) (send input-dwell set-value (number->string d)) (send hold-beats set-value (number->string h)) (send juggler-t erase) ; Why do these add extra newlines (send juggler-t insert j) (send pattern-t erase) (send pattern-t insert p)) (define juggler-ec (new editor-canvas% [parent this] [line-count 12])) (define juggler-t (new text%)) (send juggler-ec set-editor juggler-t) (define pattern-ec (new editor-canvas% [parent this] [line-count 20])) (define pattern-t (new text%)) (send pattern-ec set-editor pattern-t) ; Lots of other stuff...

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• Einmal nach oben, bitte. Mit den Oracle Communities.

  - by A&C Redaktion

  Stellen Sie sich vor, Sie treffen im Fahrstuhl einen bekannten und vertrauten Geschäftspartner. Theoretisch bleibt Ihnen nur die Fahrtzeit vom Erdgeschoss in den dritten Stock, um eine wichtige Angelegenheit zu erklären. Das nennt man „Elevator Pitch". Anwar Behan und Bernhard Adelmann haben dieses beliebte Szenario für Sie nachgestellt und erklären so auf unterhaltsame Weise, welchen Mehrwert die Oracle Communities für den Oracle Partner haben. Mit den Oracle Communities geht es für Partner nach oben und hier zum Video.

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• Help with dynamic-wind and call/cc

  - by josh

  I am having some trouble understanding the behavior of the following Scheme program: (define c (dynamic-wind (lambda () (display 'IN)(newline)) (lambda () (call/cc (lambda (k) (display 'X)(newline) k))) (lambda () (display 'OUT)(newline)))) As I understand, c will be bound to the continution created right before "(display 'X)". But using c seems to modify itself! The define above prints (as I expected) IN, X and OUT: IN X OUT And it is a procedure: #;2> c #<procedure (a9869 . results1678)> Now, I would expect that when it is called again, X would be printed, and it is not! #;3> (c) IN OUT And now c is not a procedure anymore, and a second invokation of c won't work! #;4> c ;; the REPL doesn't answer this, so there are no values returned #;5> (c) Error: call of non-procedure: #<unspecified> Call history: <syntax> (c) <eval> (c) <-- I was expecting that each invokation to (c) would do the same thing -- print IN, X, and OUT. What am I missing?

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• License similar to the MIT license but without the ability to sell?

  - by Ben

  I'm trying to decide how I want to license my Wordpress themes to the public. I know that the GPL is recommended to Wordpress theme creators, however I feel it might not be liberal enough for me because I want businesses to be able to use them if they want to. I really like the MIT license, the only thing that gets me is the freedom to sell part. I don't want someone taking my themes and selling them on some theme farm site, they should be free for everyone, however I don't want to require them to republish any changes under the MIT as well, I think that that freedom should remain intact. Is there a license that sort of fits into the terms I specified here? I'm not a lawyer so I have trouble reading through the complicated language of licenses. If there is not a similar license to the MIT but with the terms I have specified, should I just license under a modified MIT? If so, can anyone help me write it? Thanks very much!

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• What software licesnse should I release my code under?

  - by Citizen

  We're about to finish some free software and we're not sure what license we should release it under. Here's the details: The software is funded by several sponsors The software is open source The software will be free to download by the end-user The software will be free to use and modify for personal and commercial use by the end-user We want to retain ownership of the code We don't want anyone else to distribute our product What software license should we use?

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• What software license should I release my code under?

  - by Citizen

  We're about to finish some free software and we're not sure what license we should release it under. Here's the details: The software is funded by several sponsors The software is open source (edit: see comments) The software will be free to download by the end-user The software will be free to use and modify for personal and commercial use by the end-user We want to retain ownership of the code We don't want anyone else to distribute our product What software license should we use? Edit: this is a free php social arcade script. Something like a Kongregate.com clone.

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• Willkommen in der Cloud. Aber nur mit den richtigen Standards.

  - by A&C Redaktion

  Cloud Computing ist das „In"-Thema, über das Anwender, Partner und Anbieter gleichermaßen heiß diskutieren. Reinhard Arnhold, Director Channel Sales, ist ein echter Kenner der Materie und zeigt im Video die unterschiedlichen Perspektiven auf, die ein ISV einnehmen kann. Die Geschäftsmodelle erfahren durch die Möglichkeit des Cludcomputings eine neue Dimension. Für welches Modell sich ISVs hierbei auch entscheiden, den richtigen Standard bei der Lösungsarchitektur zu wählen, das ist, so Reinhard Arnhold, eine der wichtigsten Erfolgsvoraussetzungen. Für ISVs, die aktuell noch keine Cloud Computing-fähigen Anwendungen haben, hat Reinhard Arnhold eine gute Botschaft. Oracle ist vorbereitet, mit der standardisierten Oracle Architektur den ISVs den Weg in die Cloud zu bahnen. Erlauben Sie ein kleines Wortspiel: Das ist der „Stairway to heaven". Es kann also ganz einfach sein, den geschäftlichen Himmel durch die Cloud zu erreichen.

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• Please explain some of Paul Graham's points on LISP

  - by kunjaan

  I need some help understanding some of the points from Paul Graham's article http://www.paulgraham.com/diff.html A new concept of variables. In Lisp, all variables are effectively pointers. Values are what have types, not variables, and assigning or binding variables means copying pointers, not what they point to. A symbol type. Symbols differ from strings in that you can test equality by comparing a pointer. A notation for code using trees of symbols. The whole language always available. There is no real distinction between read-time, compile-time, and runtime. You can compile or run code while reading, read or run code while compiling, and read or compile code at runtime. What do these points mean How are they different in languages like C or Java? Do any other languages other than LISP family languages have any of these constructs now?

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• (1 2 3 . #<void>)- heapsort

  - by superguay

  Hello everybody: I tried to implement a "pairing heap" with all the regular operations (merge, delete-min etc.), then I've been requested to write a function that would sort a list using my newly constructed heap implementation. Unfortunately it seems that someting goes wrong... Here's the relevant code: (define (heap-merge h1 h2) (cond ((heap-empty? h1) h2) ((heap-empty? h2) h1) (else (let ((min1 (heap-get-min h1)) (min2 (heap-get-min h2))) (if ((heap-get-less h1) min1 min2) (make-pairing-heap (heap-get-less h1) min1 (cons h2 (heap-get-subheaps h1))) (make-pairing-heap (heap-get-less h1) min2 (cons h1 (heap-get-subheaps h2)))))))) (define (heap-insert element h) (heap-merge (make-pairing-heap (heap-get-less h) element '()) h)) (define (heap-delete-min h) (define (merge-in-pairs less? subheaps) (cond ((null? subheaps) (make-heap less?)) ((null? (cdr subheaps)) (car subheaps)) (else (heap-merge (heap-merge (car subheaps) (cadr subheaps)) (merge-in-pairs less? (cddr subheaps)))))) (if (heap-empty? h) (error "expected pairing-heap for first argument, got an empty heap ") (merge-in-pairs (heap-get-less h) (heap-get-subheaps h)))) (define (heapsort l less?) (let aux ((h (accumulate heap-insert (make-heap less?) l))) (if (not (heap-empty? h)) (cons (heap-get-min h) (aux (heap-delete-min h)))))) And these are some selectors that may help you to understand the code: (define (make-pairing-heap less? min subheaps) (cons less? (cons min subheaps))) (define (make-heap less?) (cons less? '())) (define (heap-get-less h) (car h)) (define (heap-empty? h) (if (null? (cdr h)) #t #f)) Now lets get to the problem: When i run 'heapsort' it returns the sorted list with "void", as you can see: (heapsort (list 1 2 3) <) (1 2 3 . #)..HOW CAN I FIX IT? Regards, Superguay

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• How to convert RGB to BGR?

  - by Adam

  This is probably easy, but I'm trying to convert from a source which provides colors in RGB strings to an output in BGR strings in Java. I've been busting my brain and time on shifting and Long.decode and Long.toHexString. Feel free to also throw alpha values in there (RGBA - ABGR), though I think I can extend the principles.

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• Override colorscheme

  - by RymdPung

  I often find myself wanting to change just something little in a colorscheme, but i don't want to edit the original file. I tried putting my change in '~/.vim/after/colors/blah.vim', but that doesn't work for me. Example, I want to change the CursorLine highlight in BusyBee.vim.. ~/.vim/colors/BusyBee.vim I create the file '~/.vim/after/colors/BusyBee.vim' and add this: hi CursorLine guibg=#000000 ctermbg=Black cterm=none However, i don't see the change. Of course it works if i change the line in the originial BusyBee.vim, but like i said i'd prefer not to do that. Doing... :colo Busy<TAB> Shows me... BusyBee BusyBee

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• DrScheme versus mzscheme: treatment of definitions

  - by speciousfool

  One long term project I have is working through all the exercises of SICP. I noticed something a bit odd with the most recent exercise. I am testing a Huffman encoding tree. When I execute the following code in DrScheme I get the expected result: (a d a b b c a) However, if I execute this same code in mzscheme by calling (load "2.67.scm") or by running mzscheme -f 2.67.scm, it reports: symbols: expected symbols as arguments, given: (leaf D 1) My question is: why? Is it because mzscheme and drscheme use different rules for loading program definitions? The program code is below. ;; Define an encoding tree and a sample message ;; Use the decode procedure to decode the message, and give the result. (define (make-leaf symbol weight) (list 'leaf symbol weight)) (define (leaf? object) (eq? (car object) 'leaf)) (define (symbol-leaf x) (cadr x)) (define (weight-leaf x) (caddr x)) (define (make-code-tree left right) (list left right (append (symbols left) (symbols right)) (+ (weight left) (weight right)))) (define (left-branch tree) (car tree)) (define (right-branch tree) (cadr tree)) (define (symbols tree) (if (leaf? tree) (list (symbol-leaf tree)) (caddr tree))) (define (weight tree) (if (leaf? tree) (weight-leaf tree) (cadddr tree))) (define (decode bits tree) (define (decode-1 bits current-branch) (if (null? bits) '() (let ((next-branch (choose-branch (car bits) current-branch))) (if (leaf? next-branch) (cons (symbol-leaf next-branch) (decode-1 (cdr bits) tree)) (decode-1 (cdr bits) next-branch))))) (decode-1 bits tree)) (define (choose-branch bit branch) (cond ((= bit 0) (left-branch branch)) ((= bit 1) (right-branch branch)) (else (error "bad bit -- CHOOSE-BRANCH" bit)))) (define (test s-exp) (display s-exp) (newline)) (define sample-tree (make-code-tree (make-leaf 'A 4) (make-code-tree (make-leaf 'B 2) (make-code-tree (make-leaf 'D 1) (make-leaf 'C 1))))) (define sample-message '(0 1 1 0 0 1 0 1 0 1 1 1 0)) (test (decode sample-message sample-tree))

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