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  • Pattern Matching in Scheme

    - by kunjaan
    How do I accept the following input? (list of 0 or more charcters and ends with 3) or (list of 1 or more characters 4 and 0 or more characters after 4) something like (match ( list 3)) -> #t (match ( list 1 2 3)) -> #t (match (list 1 2 3 4)) -> #t (match (list 1 2 3 4 5)) -> #t (match (list 4)) -> #f EDIT: THIS IS NOT MY HOMEWORK. I trying to write something like ELIZA from PAIP but I know only how to write a pattern that begins with a word.

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  • Please Help me add up the elements for this structure in Scheme/Lisp

    - by kunjaan
    I have an input which is of this form: (((lady-in-water . 1.25) (snake . 1.75) (run . 2.25) (just-my-luck . 1.5)) ((lady-in-water . 0.8235294117647058) (snake . 0.5882352941176471) (just-my-luck . 0.8235294117647058)) ((lady-in-water . 0.8888888888888888) (snake . 1.5555555555555554) (just-my-luck . 1.3333333333333333))) (context: the word denotes a movie and the number denotes the weighted rating submitted by the user) I need to add all the quantity and return a list which looks something like this ((lady-in-water 2.5) (snake 2.5) (run 2.25) (just-myluck 2.6)) How do I traverse the list and all the quantities? I am really stumped. Please help me. Thanks.

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  • Scheme: what are the benefits of letrec?

    - by Ixmatus
    While reading "The Seasoned Schemer" I've begun to learn about letrec. I understand what it does (can be duplicated with a Y-Combinator) but the book is using it in lieu of recurring on the already defined function operating on arguments that remain static. An example of an old function using the defined function recurring on itself (nothing special): (define (substitute new old lat) (cond ((null? l) '()) ((eq? (car l) old) (cons new (substitute new old (cdr l)))) (else (cons (car l) (substitute new old (cdr l)))))) Now for an example of that same function but using letrec: (define (substitute new old lat) (letrec ((replace (lambda (l) (cond ((null? l) '()) ((eq? (car l) old) (cons new (replace (cdr l)))) (else (cons (car l) (replace (cdr l)))))))) (replace lat))) Aside from being slightly longer and more difficult to read I don't know why they are rewriting functions in the book to use letrec. Is there a speed enhancement when recurring over a static variable this way because you don't keep passing it?? Is this standard practice for functions with arguments that remain static but one argument that is reduced (such as recurring down the elements of a list)? Some input from more experienced Schemers/LISPers would help!

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  • Types in Lisp and Scheme

    - by user2054900
    I see now that Racket has types. At first glance it seems to be almost identical to Haskell typing. But is Lisp's CLOS covering some of the space Haskell types cover? Creating a very strict Haskell type and an object in any OO language seems vaguely similar. It's just that I've drunk some of the Haskell kool-aid and I'm totally paranoid that if I go down the Lisp road, I'll be screwed due to dynamic typing.

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  • What is the meaning of # in R5RS Scheme number literals

    - by ikmac
    There is a partial answer on Stack Overflow, but I'm asking something a teeny bit more specific than the answers there. So... Does the formal semantics (Section 7.2) specify the meaning of such a numeric literal? Does it specify the meaning of numeric operations on the value resulting from interpreting the literal? If yes, what are the meanings (in English -- denotational semantics is all greek characters to me :))?

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  • How do I make a module in PLT Scheme?

    - by kunjaan
    I tried doing this: #lang scheme (module duck scheme/base (provide num-eggs quack) (define num-eggs 2) (define (quack n) (unless (zero? n) (printf "quack\n") (quack (sub1 n))))) But I get this error: module: illegal use (not at top-level) in: (module duck scheme/base (provide num-eggs quack) (define num-eggs 2) (define (quack n) (unless (zero? n) (printf "quack\n") (quack (sub1 n))))) what is the correct way?

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  • Is there an equivalent to Lisp's "runtime" primitive in Scheme?

    - by Bill the Lizard
    According to SICP section 1.2.6, exercise 1.22: Most Lisp implementations include a primitive called runtime that returns an integer that specifies the amount of time the system has been running (measured, for example, in microseconds). I'm using DrScheme, where runtime doesn't seem to be available, so I'm looking for a good substitute. I found in the PLT-Scheme Reference that there is a current-milliseconds primitive. Does anyone know if there's a timer in Scheme with better resolution?

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  • [MINI HOW-TO] Change the Default Color Scheme in Office 2010

    - by Mysticgeek
    Like in Office 2007 the default color scheme for 2010 is blue. If you are not a fan of it, here we show you how to change it to silver or black. In this example we are using Microsoft Word, but it works the same way in Excel, Outlook, and PowerPoint as well. Once you change the color scheme in one Office application, it will change it for all of the other apps in the suite. Change Color Scheme To change the color scheme click on the File tab to access Backstage View and click on Options. In Word Options the General section should open by default…use the dropdown menu next to Color Scheme to change it to Silver, Blue, or Black then click OK. Here is what Black looks like…who knows why Microsoft decided to leave the blue around the edges. This is the default Blue color scheme… And finally we take a look at the Silver color scheme in Excel… That is all there is to it! It would be nice if they would incorporate other color schemes to Office 2010, as some of you may not be happy with only three choices. If you’re using Office 2007 check out our article on how to change the color scheme in it. Also, The Geek has a cool article on how to set the Color Scheme of Office 2007 with a quick registry hack. Similar Articles Productive Geek Tips Set the Office 2007 Color Scheme With a Quick Registry HackChange The Default Color Scheme In Office 2007Maximize Space by "Auto-Hiding" the Ribbon in Office 2007How To Personalize the Windows Command PromptOrganize & Group Your Tabs in Firefox the Easy Way TouchFreeze Alternative in AutoHotkey The Icy Undertow Desktop Windows Home Server – Backup to LAN The Clear & Clean Desktop Use This Bookmarklet to Easily Get Albums Use AutoHotkey to Assign a Hotkey to a Specific Window Latest Software Reviews Tinyhacker Random Tips Xobni Plus for Outlook All My Movies 5.9 CloudBerry Online Backup 1.5 for Windows Home Server Snagit 10 2010 World Cup Schedule Boot Snooze – Reboot and then Standby or Hibernate Customize Everything Related to Dates, Times, Currency and Measurement in Windows 7 Google Earth replacement Icon (Icons we like) Build Great Charts in Excel with Chart Advisor tinysong gives a shortened URL for you to post on Twitter (or anywhere)

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  • In PLT scheme, can I export functions after another function has been called?

    - by Jason Baker
    I'm trying to create a binding to libpython using scheme's FFI. To do this, I have to get the location of python, create the ffi-lib, and then create functions from it. So for instance I could do this: (module pyscheme scheme (require foreign) (unsafe!) (define (link-python [lib "/usr/lib/libpython2.6.so"]) (ffi-lib lib)) This is all well and good, but I can't think of a way to export functions. For instance, I could do something like this: (define Py_Initialize (get-ffi-obj "Py_Initialize" libpython (_fun -> _void))) ...but then I'd have to store a reference to libpython (created by link-python) globally somehow. Is there any way to export these functions once link-python is called? In other words, I'd like someone using the module to be able to do this: (require pyscheme) (link-python) (Py_Initialize) ...or this: (require pyscheme) (link-python "/weird/location/for/libpython.so") (Py_Initialize) ...but have this give an error: (require pyscheme) (Py_Initialize) How can I do this?

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  • "unbound identifier" errors in scheme

    - by user186909
    Hello: I'm using drscheme from: http://www.archlinux.org/packages/extra/x86_64/drscheme/ I'm trying to work with the sample code in my textbook, but I keep getting getting "unbound identifier" errors. Is it because the scheme interpreter is not configured correctly? or is the code just plain wrong? Here are a few examples: Input: #lang scheme (define (equalimp lis1 lis2) (COND ((NULL? lis1) (NULL? lis2)) ((NULL? lis2) '()) ((EQ? (CAR lis1) (CAR lis2)) (equalimp (CDR lis1) (CDR lis2))) (ELSE '()) )) Output: Welcome to DrScheme, version 4.2.5 [3m]. Language: scheme; memory limit: 128 MB. expand: unbound identifier in module in: COND Input: #lang scheme (define (quadratic_roots a b c) (LET ( (root_part_over_2a (/ (SQRT (- (* b b) (* 4 a c))) (* 2 a))) (minus_b_over_2a (/ (- 0 b) (* 2 a))) ) (DISPLAY (+ minus_b_over_2a root_part_over_2a)) (NEWLINE) (DISPLAY (- minus_b_over_2a root_part_over_2a)) )) Output: expand: unbound identifier in module in: LET Note: I tried using LET* because I read this: stackoverflow.com/ questions/946050/using-let-in-scheme but it produces the same error. Thanks !

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  • How do I define functions using PLT Scheme macros?

    - by nickname
    I am trying to write a macro that defines a special class of data structure with associated functions. I know this is possible; it is done multiple times in the core language itself. As a specific example, how would I define the define-struct macro in Scheme itself. It needs to create make-struct, struct-<<field>>, etc functions. I tried doing this using define, however, this only defines the function in the macro's lexical scope. How can I actually define a function in a macro?

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  • How do I use Declarations (type, inline, optimize) in Scheme?

    - by kunjaan
    How do I declare the types of the parameters in order to circumvent type checking? How do I optimize the speed to tell the compiler to run the function as fast as possible like (optimize speed (safety 0))? How do I make an inline function in Scheme? How do I use an unboxed representation of a data object? And finally are any of these important or necessary? Can I depend on my compiler to make these optimizations? thanks, kunjaan.

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  • Writing an auto-memoizer in Scheme. Help with macro and a wrapper.

    - by kunjaan
    I am facing a couple of problems while writing an auto-memoizer in Scheme. I have a working memoizer function, which creats a hash table and checks if the value is already computed. If it has been computed before then it returns the value else it calls the function. (define (memoizer fun) (let ((a-table (make-hash))) (?(n) (define false-if-fail (?() #f)) (let ((return-val (hash-ref a-table n false-if-fail))) (if return-val return-val (begin (hash-set! a-table n (fun n)) (hash-ref a-table n))))))) Now I want to create a memoize-wrapper function like this: (define (memoize-wrapper function) (set! function (memoizer function))) And hopefully create a macro called def-memo which defines the function with the memoize-wrapper. eg. the macro could expand to (memoizer (define function-name arguments body ...) or something like that. So that I should be able to do : (def-memo (factorial n) (cond ((= n 1) 1) (else (* n (factorial (- n 1)))))) which should create a memoized version of the factorial instead of the normal slow one. My problem is that the The memoize-wrapper is not working properly, it doesnt call the memoized function but the original function. I have no idea how to write a define inside of the macro. How do I make sure that I can get variable lenght arguments and variable length body? How do I then define the function and wrap it around with the memoizer? Thanks a lot.

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  • Scheme vs Haskell for an Introduction to Functional Programming?

    - by haziz
    I am comfortable with programming in C and C#, and will explore C++ in the future. I may be interested in exploring functional programming as a different programming paradigm. I am doing this for fun, my job does not involve computer programming, and am somewhat inspired by the use of functional programming, taught fairly early, in computer science courses in college. Lambda calculus is certainly beyond my mathematical abilities, but I think I can handle functional programming. Which of Haskell or Scheme would serve as a good intro to functional programming? I use emacs as my text editor and would like to be able to configure it more easily in the future which would entail learning Emacs Lisp. My understanding, however, is that Emacs Lisp is fairly different from Scheme and is also more procedural as opposed to functional. I would likely be using "The Little Schemer" book, which I have already bought, if I pursue Scheme (seems to me a little weird from my limited leafing through it). Or would use the "Learn You a Haskell for Great Good" if I pursue Haskell. I would also watch the Intro to Haskell videos by Dr Erik Meijer on Channel 9. Any suggestions, feedback or input appreciated. Thanks. P.S. BTW I also have access to F# since I have Visual Studio 2010 which I use for C# development, but I don't think that should be my main criteria for selecting a language.

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  • Creating custom URI scheme using URI class

    - by Sorantis
    I need to create a custom URI scheme for my project. i.e urn:myprotocol:{p1}:{p2}:{p3}:{p4} - opaque representation myprotocol://{p1}/{p2}/{p3}/{p4} - hierarchical representation. How can I add my scheme to Java URI class? Or, how can I make Java URI to understand my scheme, so I could use it in my code? Concrete examples are welcome. Thanks.

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  • How to compile scheme into native binary files ?

    - by Joe
    I am very new to scheme. And now I am trying to compile some scheme code into binary file which will be loaded faster into interpreter. (The interpreter is a hybrid interpreter)Some one told me that I can compile the code into native binary file and then load it into interperter. And my question is: 1. What is the native binary file? 2. How can I compile the scheme code into a native binary file? 3. How can I load native bianry file into scheme interpreter? Thanks in advance. Joe Suggested that I want to compile below code into native binary file: (define test (lambda() (display "this is a test")) And then load the bianry file into interpreter and call the function "test".

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  • What software has been written in Scheme?

    - by skiphoppy
    I loved Scheme in the programming languages concepts class I took several years ago. Ever since reading what Paul Graham has to say about Lisp, I've been intending to go back and pick Scheme up again and see if it'll improve my programming in general. Are there any well-known works of software written in Scheme? Open source packages? Websites?

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  • Does Scheme work with Microsoft COM?

    - by Martin
    I'm new to Scheme -- the functional programming language and I like it a lot for its first-class/higher-order functions. However, my data comes from a COM source with an object-oriented API. I know Scheme and COM belong to different programming paradigms, but I'm wondering if there is any interface or a way for Scheme to connect to a COM source? Thanks.

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  • How do I learn Scheme?

    - by Gautam
    Hey, I'm a relative newbie to programming. I've picked up some very basic Java (File I/O, GUIs, inheritance) and would like to take a look at functional programming - in particular, I would like to learn Scheme. I'm having some trouble finding a Scheme implementation I can understand. Interpreters are weird; I'm not sure how to save my programs and create executables. I've downloaded PLT Scheme, but I would prefer using something less condescending, something similar to NetBeans. Is there a plugin or tool that will allow me to quickly and easily create and manage Scheme programs? All help is appreciated!

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  • If Scheme is untyped, how can it have numbers and lists?

    - by Dokkat
    Scheme is said to be just an extension of the Untyped Lambda Calculus (correct me if I am wrong). If that is the case, how can it have Lists and Numbers? Those, to me, look like 2 base types. So I'd say Racket is actually an extension of the Simply Typed Lambda Calculus. No? Question: Is Scheme's type system actually based or more similar to Simply Typed or Untyped Lambda Calculus? In what ways does it differ from Untyped and or Simply Typed Lambda Calculus? (The same question is valid for "untyped" languages such as Python and JavaScript - all of which look like they have base types to me.)

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  • Idiomatic usage of filter, map, build-list and local functions in Racket/Scheme?

    - by Greenhorn
    I'm working through Exercise 21.2.3 of HtDP on my own and was wondering if this is idiomatic usage of the various functions. This is what I have so far: (define-struct ir (name price)) (define list-of-toys (list (make-ir 'doll 10) (make-ir 'robot 15) (make-ir 'ty 21) (make-ir 'cube 9))) ;; helper function (define (price< p toy) (cond [(< (ir-price toy) p) toy] [else empty])) (define (eliminate-exp ua lot) (cond [(empty? lot) empty] [else (filter ir? (map price< (build-list (length lot) (local ((define (f x) ua)) f)) lot))])) To my novice eyes, that seems pretty ugly because I have to define a local function to get build-list to work, since map requires two lists of equal length. Can this be improved for readability? Thank you.

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  • How do I write Push and Pop in Scheme?

    - by kunjaan
    Right now I have (define (push x a-list) (set! a-list (cons a-list x))) (define (pop a-list) (let ((result (first a-list))) (set! a-list (rest a-list)) result)) But I get this result: Welcome to DrScheme, version 4.2 [3m]. Language: Module; memory limit: 256 megabytes. > (define my-list (list 1 2 3)) > (push 4 my-list) > my-list (1 2 3) > (pop my-list) 1 > my-list (1 2 3) What am I doing wrong? Is there a better way to write push so that the element is added at the end and pop so that the element gets deleted from the first?

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