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  • Extracting fields from a define-type object in Scheme

    - by Mike
    Hi, I am trying to extract the field 'name' or 'named-expr' from the following object: (bind 'x (num 5)) ;; note that this is not a list, but a type Binding With the Binding definition: (define-type Binding (bind (name symbol?) (named-expr WAE?))) I have tried, but received the error "reference to an identifier before its definition: Binding-name." Here is what I tried typing: (begin (Binding-name (bind 'x (num 5)))) (begin (define x (bind 'x (num 5))) (Binding-name x)) Thank you!

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  • Find all paths from root to leaves of tree in Scheme

    - by grifaton
    Given a tree, I want to find the paths from the root to each leaf. So, for this tree: D / B / \ A E \ C-F-G has the following paths from root (A) to leaves (D, E, G): (A B D), (A B E), (A C F G) If I represent the tree above as (A (B D E) (C (F G))) then the function g does the trick: (define (g tree) (cond ((empty? tree) '()) ((pair? tree) (map (lambda (path) (if (pair? path) (cons (car tree) path) (cons (car tree) (list path)))) (map2 g (cdr tree)))) (else (list tree)))) (define (map2 fn lst) (if (empty? lst) '() (append (fn (car lst)) (map2 fn (cdr lst))))) But this looks all wrong. I've not had to do this kind of thinking for a while, but I feel there should be a neater way of doing it. Any ideas for a better solution (in any language) would be appreciated.

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  • Getting the median of 3 values using scheme's car & cdr

    - by kristian Roger
    The problem this time is to get the median of three values (easy) I did this: (define (med x y z) (car(cdr(x y z))) and it was accepted but when testing it: (med 3 4 5) I get this error: Error: attempt to call a non-procedure (2 3 4) And when entering letters instead of number i get: (md x y z) Error: undefined varia y (package user) Using something besides x y z I get: (md d l m) Error: undefined variable d (package user) the question was deleted dont know how anyway write a function that return the median of 3 values

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  • Problem with circular definition in Scheme

    - by user8472
    I am currently working through SICP using Guile as my primary language for the exercises. I have found a strange behavior while implementing the exercises in chapter 3.5. I have reproduced this behavior using Guile 1.4, Guile 1.8.6 and Guile 1.8.7 on a variety of platforms and am certain it is not specific to my setup. This code works fine (and computes e): (define y (integral (delay dy) 1 0.001)) (define dy (stream-map (lambda (x) x) y)) (stream-ref y 1000) The following code should give an identical result: (define (solve f y0 dt) (define y (integral (delay dy) y0 dt)) (define dy (stream-map f y)) y) (solve (lambda (x) x) 1 0.001) But it yields the error message: standard input:7:14: While evaluating arguments to stream-map in expression (stream-map f y): standard input:7:14: Unbound variable: y ABORT: (unbound-variable) So when embedded in a procedure definition, the (define y ...) does not work, whereas outside the procedure in the global environment at the REPL it works fine. What am I doing wrong here? I can post the auxiliary code (i.e., the definitions of integral, stream-map etc.) if necessary, too. With the exception of the system-dependent code for cons-stream, they are all in the book. My own implementation of cons-stream for Guile is as follows: (define-macro (cons-stream a b) `(cons ,a (delay ,b)))

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  • Scheme: Mysterious void in pattern match.

    - by Schemer
    Hi. I am writing a function called annotate that uses match-lambda -- often with recursive calls to annotate. Here is one of the pattern matches: (`(lambda (,<param1> . ,<params>) ,<stmts>) `(CLOSURE ENV (,<param1> . ,<params>) (lambda (ENV) ,(map annotate (map (lambda (x) (append `(,<param1> . ,<params>) (list x))) `(,<stmts>)))))) However, when this pattern is matched this is what returns: '(CLOSURE ENV (x) (lambda (ENV) ((CLOSURE ENV (x y) (lambda (ENV) ((+ x y)))))) #<void>) Specifically I can't figure out where "void" is coming from. In fact, if I include the line: ,(displayln (map annotate (map (lambda (x) (append `(,<param1> . ,<params>) (list x))) `(,<stmts>)))) it prints: ((CLOSURE ENV (x y) (lambda (ENV) ((+ x y))))) notably without "void". If someone could tell me what the problem is it would be greatly appreciated. Thanks.

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  • make tree in scheme

    - by ???
    (define (entry tree) (car tree)) (define (left-branch tree) (cadr tree)) (define (right-branch tree) (caddr tree)) (define (make-tree entry left right) (list entry left right)) (define (mktree order items_list) (cond ((= (length items_list) 1) (make-tree (car items_list) '() '())) (else (insert2 order (car items_list) (mktree order (cdr items_list)))))) (define (insert2 order x t) (cond ((null? t) (make-tree x '() '())) ((order x (entry t)) (make-tree (entry t) (insert2 order x (left-branch t)) (right-branch t))) ((order (entry t) x ) (make-tree (entry t) (left-branch t) (insert2 order x (right-branch t)))) (else t))) The result is: (mktree (lambda (x y) (< x y)) (list 7 3 5 1 9 11)) (11 (9 (1 () (5 (3 () ()) (7 () ()))) ()) ()) But I'm trying to get: (7 (3 (1 () ()) (5 () ())) (9 () (11 () ()))) Where is the problem?

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  • using lambda instead of let in scheme

    - by Radagaisus
    Hey, In SICP 1.2.1 there is a function that makes a rational number, as follow: (define (make-rat n d) (let ((g (gcd n d))) (cons (/ n g) (/ d g)))) I'm just curious how you can implement the same thing using lambda instead of let, without calling GCD twice. I couldn't figure it out myself.

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  • Writing an Eval Procedure in Scheme?

    - by Planeman
    My problem isn't with the built-in eval procedure but how to create a simplistic version of it. Just for starters I would like to be able to take this in '(+ 1 2) and have it evaluate the expression + where the quote usually takes off the evaluation. I have been thinking about this and found a couple things that might be useful: Unquote: , (quasiquote) (apply) My main problem is regaining the value of + as a procedure and not a symbol. Once I get that I think I should just be able to use it with the other contents of the list. Any tips or guidance would be much appreciated.

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  • What color scheme do you use for programming?

    - by EndangeredMassa
    I get a lot of attention at work because I am the only one who bothered to change the default color settings in Visual Studio. I just modified them myself. I can provide the settings file if anyone cares to import it. Here's an example of how it looks. It reminds me of DOS/BASIC programming before I actually knew how to program. I also find it to be very readable. What color schemes do you use?! EDIT: To clarify, I only edited the text settings. The windows and panels of VS2005 are still the windows default.

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  • True / false evaluation doesn't work as expected in Scheme

    - by ron
    I'm trying to compare two booleans : (if (equal? #f (string->number "123b")) "not a number" "indeed a number") When I run this in the command line of DrRacket I get "not a number" , however , when I put that piece of code in my larger code , the function doesn't return that string ("not a number") , here's the code : (define (testing x y z) (define badInput "ERROR") (if (equal? #f (string->number "123b")) "not a number" "indeed a number") (display x)) And from command line : (testing "123" 1 2) displays : 123 Why ? Furthermore , how can I return a value , whenever I choose ? Here is my "real" problem : I want to do some input check to the input of the user , but the thing is , that I want to return the error message if I need , before the code is executed , because if won't - then I would run the algorithm of my code for some incorrect input : (define (convert originalNumber s_oldBase s_newBase) (define badInput "ERROR") ; Input check - if one of the inputs is not a number then return ERROR (if (equal? #f (string->number originalNumber)) badInput) (if (equal? #f (string->number s_oldBase)) badInput) (if (equal? #f (string->number s_newBase)) badInput) (define oldBase (string->number s_oldBase)) (define newBase (string->number s_newBase)) (define outDecimal (convertIntoDecimal originalNumber oldBase)) (define result "") ; holds the new number (define remainder 0) ; remainder for each iteration (define whole 0) ; the whole number after dividing (define temp 0) (do() ((= outDecimal 0)) ; stop when the decimal value reaches 0 (set! whole (quotient outDecimal newBase)) ; calc the whole number (set! temp (* whole newBase)) (set! remainder (- outDecimal temp)) ; calc the remainder (set! result (appending result remainder)) ; append the result (set! outDecimal (+ whole 0)) ; set outDecimal = whole ) ; end of do (if (> 1 0) (string->number (list->string(reverse (string->list result))))) ) ;end of method This code won't work since it uses another method that I didn't attach to the post (but it's irrelevant to the problem . Please take a look at those three IF-s ... I want to return "ERROR" if the user put some incorrect value , for example (convert "23asb4" "b5" "9") Thanks

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  • Scheme Function to reverse elements of list of 2-list

    - by sudhirc
    This is an exercise from EOPL. Procedure (invert lst) takes lst which is a list of 2-lists and returns a list with each 2-list reversed. (define invert (lambda (lst) (cond((null? lst ) '()) ((= 2 (rtn-len (car lst))) ( cons(swap-elem (car lst)) (invert (cdr lst)))) ("List is not a 2-List")))) ;; Auxiliry Procedure swap-elements of 2 element list (define swap-elem (lambda (lst) (cons (car (cdr lst)) (car lst)))) ;; returns lengh of the list by calling (define rtn-len (lambda (lst) (calc-len lst 0))) ;; calculate length of the list (define calc-len (lambda (lst n) (if (null? lst) n (calc-len (cdr lst) (+ n 1))))) This seems to work however looks very verbose. Can this be shortened or written in more elegant way ? How I can halt the processing in any of the individual element is not a 2-list? At the moment execution proceed to next member and replacing current member with "List is not a 2-List" if current member is not a 2-list.

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  • If item not in the lst in scheme

    - by ms. sakura
    I'm working on context-free grammars, and I have a function that returns the (terminal values of grammar) for example: i have non-terminal function that results in (A B) , from calling say ((A cat) (B happy np) (A B sad)) so technically A and B are non terminals of the grammar. Now I want to be able to get the terminals (cat happy np sad) (define terminals (lambda (lsts) (cond ((null? lsts) lsts) ((not(member? (car(car lsts)) (n-terminals lsts))) (cons (car(car lsts)) (terminals (car (cdr lsts))))) (else (terminals (cdr lsts)))))) PS: functionality of n-terminals is described above. member? is a boolean function that returns true if an item is a member of the list, false otherwise. My function returns an empty lst. What am I missing here?

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  • Finding greatest product of two lists, but keep getting #unspecific

    - by user1787030
    (define (greatest-product lst1 lst2) (define (helper lst addtimes total toacc) (cond ((null? lst) '()) ((= (countatoms lst) 1) (display total)) ((= addtimes (cadr lst)) (helper (cdr lst) 1 total total)) (else (helper lst (+ 1 addtimes) (+ toacc total) toacc)))) (cond ((> (helper lst1 0 0 (car lst1)) (helper lst2 0 0 (car lst2))) (helper lst1 0 0 (car lst1))) ((< (helper lst1 0 0 (car lst1)) (helper lst2 0 0 (car lst2))) (helper lst2 0 0 (car lst2))) ((= (helper lst1 0 0 (car lst1)) (helper lst2 0 0 (car lst2))) (display 'equal)))) Scheme keeps returning back that it cannot perform the procedure with #unspecific Im running it with (display (greatest-product '(1 2 3) '(4 5 6))) (display (greatest-product '(1 2 3) '(1 2 3))) (display (greatest-product '(1 2 3) '())) what is wrong with it? the problem seems to be occurring

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  • Recover lost NTFS partition on SSD

    - by Emil
    Hello, About 2 month ago I upgraded my Dell Latitude E6500 laptop with a Corsair Force F120 SSD drive. Everything worked well until about a week or so back. I started the computer and was faced with a beep and a message saying "No boot sector on Internal HDD (IRRT). No bootable devices". Since I figured that the boot sector had somehow got corrupt I tried booting from the Windows 7 dvd in order to repair the boot sector. But the Windows 7 installation program only found a blank drive with 111GB of unallocated space. I panicked and brought the drive with me to work to let a colleague have a look at it. We made a disk image of the entire drive and ran the drive through Testdisk in Linux. Testdisk did not find any partitions. It appears that the drive has been completely erased... What has happened? What is causing this behavior on an SSD?

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  • partition alignment on fresh windows 2003 ent server

    - by Datapimp23
    Hi, I have this server which has it's physical disks in RAID 5 controlled by a 3com raid controller. size of the stripe unit is unknown for the moment (Can check tomorrow in the office). I need to install windows server 2003 ENT and create 2 partitions (OS, Data). I'd like to create the partitions before the installation on windows server. They have to be aligned properly. I have the newest version of gparted on a disc but I have no clue if this is the right tool. Can someone point me in the right direction? Thanks

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  • df shows partition as full, but du shows it as only 25% full

    - by Jakobud
    I have a humble linux server to do some stuff for me. I only have an old 16gig drive in it. df -h Filesystem Size Used Avail Use% Mounted on /dev/md1 16G 16G 0 100% / /dev/md0 121M 14M 101M 13% /boot tmpfs 502M 0 502M 0% /dev/shm but when I do: du -sh / 3.5G / So one says that my 16G drive is full. The other says only 3.5G is used. Why the discrepancy? I cannot write any new files as it says the drive is indeed full. But if I can't find the files taking up all the space on the file-system, how can I delete them to free up space?

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  • Moving Bootcamp partition to another drive

    - by Xster
    Hi, I don't know how sketch this is. I currently have Bootcamp with Windows 7 on my internal along with my Snow Leopard. I'm moving to a bigger harddrive. I'm reinstalling Snow Leopard but I would like to keep my Bootcamp. How do I migrate the data from one drive to another? Any suggestions? I'm not willing to spend money on this

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  • Unable to create system partition or locate existing system partition during Windows-7 installation

    - by glenneroo
    I have Windows XP 32-bit installed on an ASUS A8N-SLI Deluxe with 2x 500gb drives in RAID1 using the NV RAID controller. On this there are 3 partitions (XP, XP backup and DATA) There are also 4x 500gb drives in RAID10 using the Silicon Image 3114R RAID controller. I just purchased a Windows 7 64-bit as an ISO download upgrade version which I promptly burned to DVD and attempted to perform an upgrade installation. Here is the error message I am getting: Firstly, where are these "Setup log files" located? Second, does this mean I need to find compatible (64-bit?) drivers for the Mainboard and put them on floppy? EDIT: As suggested on another forum, I tried downloading the nVidia Mainboard RAID drivers for Windows 2003 64-bit. I loaded the drivers successfully using the Load Driver button, but pressing NEXT still returns this error.

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  • Root partition full? CentOS

    - by Joao Heleno
    Hi! I'm running CentOS 5.4 and my / is full. I wanted to install gparted but in order to do that I must install Priorities and it's when I get an error saying / is full so I can't go forward. Here's some output: fdisk -l Disk /dev/sda: 250.0 GB, 250000000000 bytes 255 heads, 63 sectors/track, 30394 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Device Boot Start End Blocks Id System /dev/sda1 * 1 2611 20972826 83 Linux /dev/sda2 2612 3251 5140800 82 Linux swap / Solaris /dev/sda3 3252 30394 218026147+ 83 Linux df Filesystem 1K-blocks Used Available Use% Mounted on /dev/sda1 20315812 19365152 0 100% / /dev/sda3 211196248 49228164 151066780 25% /home tmpfs 1552844 0 1552844 0% /dev/shm I'm not using LVM. Please advise. Thanks

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  • re-partition a disk

    - by veggiemexicalidog
    I have one disk partitioned into 2 logical drives, C and D. There is no unallocated space. I need to add space to C: so I want to use some space from D (plenty available). How can I do this without losing data on D:? Edit: This is a Windows machine.

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  • Resizing an existing linux partition during Ubuntu install

    - by Richard100
    Hello All, I have Fedora Core 10 installed on a PC, occupying the whole disk (no free space). I want to add Ubuntu 10.04 desktop edition. Does Ubuntu 10.04 allow you to resize existing partitions during the installation process in order to free up some space for the Ubuntu installation? Without losing or trashing existing data, obviously. Thanks.

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  • Cause of lost partition replaced by 2 Raw partitions

    - by DwightSampsonite
    Hi, I had a curious problem over the weekend... My 500gb WD hard drive all of a sudden could not be discovered by xp, then when I plugged in again via USB it was being discovered as 2 separate Raw partitions that were asking to be formatted. I have never modified partitions on this drive before. I was scratching my head for about this for 20mins or so when my second 1TB external hard drive did the exact same thing(with the same sized raw partitions as the 500gb). I have since recovered the original partitions and data using Testdisk . I am more curious on the cause.... I suspect this could be a virus, however my machine hadn’t been online in a few days and AVG didn’t detect anything. Has anyone seen this before?

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  • What is the use of "Partition" keyword in MySQL?

    - by chandru_cp
    As I am a MySQL newbie. What does PARTITION mean in this MySQL statement? CREATE TABLE employees ( id INT NOT NULL, fname VARCHAR(30), lname VARCHAR(30), hired DATE NOT NULL DEFAULT '1970-01-01', separated DATE NOT NULL DEFAULT '9999-12-31', job_code INT NOT NULL, store_id INT NOT NULL ) PARTITION BY RANGE (store_id) ( PARTITION p0 VALUES LESS THAN (6), PARTITION p1 VALUES LESS THAN (11), PARTITION p2 VALUES LESS THAN (16), PARTITION p3 VALUES LESS THAN (21) );

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