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  • What Scheme Does Ghuloum Use?

    - by Don Wakefield
    I'm trying to work my way through Compilers: Backend to Frontend (and Back to Front Again) by Abdulaziz Ghuloum. It seems abbreviated from what one would expect in a full course/seminar, so I'm trying to fill in the pieces myself. For instance, I have tried to use his testing framework in the R5RS flavor of DrScheme, but it doesn't seem to like the macro stuff: src/ghuloum/tests/tests-driver.scm:6:4: read: illegal use of open square bracket I've read his intro paper on the course, An Incremental Approach to Compiler Construction, which gives a great overview of the techniques used, and mentions a couple of Schemes with features one might want to implement for 'extra credit', but he doesn't mention the Scheme he uses in the course. Update I'm still digging into the original question (investigating options such as Petit Scheme suggested by Eli below), but found an interesting link relating to Gholoum's work, so I am including it here. [Ikarus Scheme](http://en.wikipedia.org/wiki/Ikarus_(Scheme_implementation)) is the actual implementation of Ghuloum's ideas, and appears to have been part of his Ph.D. work. It's supposed to be one of the first implementations of R6RS. I'm trying to install Ikarus now, but the configure script doesn't want to recognize my system's install of libgmp.so, so my problems are still unresolved. Example The following example seems to work in PLT 2.4.2 running in DrEd using the Pretty Big (require lang/plt-pretty-big) (load "/Users/donaldwakefield/ghuloum/tests/tests-driver.scm") (load "/Users/donaldwakefield/ghuloum/tests/tests-1.1-req.scm") (define (emit-program x) (unless (integer? x) (error "---")) (emit " .text") (emit " .globl scheme_entry") (emit " .type scheme_entry, @function") (emit "scheme_entry:") (emit " movl $~s, %eax" x) (emit " ret") ) Attempting to replace the require directive with #lang scheme results in the error message foo.scm:7:3: expand: unbound identifier in module in: emit which appears to be due to a failure to load tests-driver.scm. Attempting to use #lang r6rs disables the REPL, which I'd really like to use, so I'm going to try to continue with Pretty Big. My thanks to Eli Barzilay for his patient help.

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  • Multidimensional vectors in scheme?

    - by incrediman
    I earlier asked a question about arrays in scheme (turns out they're called vectors but are basically otherwise the same as you'd expect). Is there an easy way to do multidimensional arrays vectors in PLT Scheme though? For my purposes I'd like to have a procedure called make-multid-vector or something. By the way if this doesn't already exist, I don't need a full code example of how to implement it. If I have to roll this myself I'd appreciate some general direction though. The way I'd probably do it is to just iterate through each element of the currently highest dimension of the vector to add another dimension, but I can see that being a bit ugly using scheme's recursive setup. Also, this seems like something I should have been able to find myself so please know that I did actually google it and nothing came up.

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  • Write Scheme data structures so they can be eval-d back in, or alternative

    - by Jesse Millikan
    I'm writing an application (A juggling pattern animator) in PLT Scheme that accepts Scheme expressions as values for some fields. I'm attempting to write a small text editor that will let me "explode" expressions into expressions that can still be eval'd but contain the data as literals for manual tweaking. For example, (4hss->sexp "747") is a function call that generates a legitimate pattern. If I eval and print that, it becomes (((7 3) - - -) (- - (4 2) -) (- (7 2) - -) (- - - (7 1)) ((4 0) - - -) (- - (7 0) -) (- (7 2) - -) (- - - (4 3)) ((7 3) - - -) (- - (7 0) -) (- (4 1) - -) (- - - (7 1))) which can be "read" as a string, but will not "eval" the same as the function. For this statement, of course, what I need would be as simple as (quote (((7 3... but other examples are non-trivial. This one, for example, contains structs which print as vectors: pair-of-jugglers ; --> (#(struct:hand #(struct:position -0.35 2.0 1.0) #(struct:position -0.6 2.05 1.1) 1.832595714594046) #(struct:hand #(struct:position 0.35 2.0 1.0) #(struct:position 0.6 2.0500000000000003 1.1) 1.308996938995747) #(struct:hand #(struct:position 0.35 -2.0 1.0) #(struct:position 0.6 -2.05 1.1) -1.3089969389957472) #(struct:hand #(struct:position -0.35 -2.0 1.0) #(struct:position -0.6 -2.05 1.1) -1.8325957145940461)) I've thought of at least three possible solutions, none of which I like very much. Solution A is to write a recursive eval-able output function myself for a reasonably large subset of the values that I might be using. There (probably...) won't be any circular references by the nature of the data structures used, so that wouldn't be such a long job. The output would end up looking like `(((3 0) (... ; ex 1 `(,(make-hand (make-position ... ; ex 2 Or even worse if I could't figure out how to do it properly with quasiquoting. Solution B would be to write out everything as (read (open-input-string "(big-long-s-expression)")) which, technically, solves the problem I'm bringing up but is... ugly. Solution C might be a different approach of giving up eval and using only read for parsing input, or an uglier approach where the s-expression is used as directly data if eval fails, but those both seem unpleasant compared to using scheme values directly. Undiscovered Solution D would be a PLT Scheme option, function or library I haven't located that would match Solution A. Help me out before I start having bad recursion dreams again.

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  • Fetch elements from List in scheme

    - by fireball003
    Hi, How to go through a list or fetch element from a list in scheme? How can I name each element (like we do for variables in java) in a list? Thanks in advance. I want to compare every point in a list to another point. So, as we do in java or python- for(int i;i<list.size();i++){ if (list[i]> k){ //do something } } How can I do similar thing in scheme?

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  • Practical Scheme Programming

    - by Ixmatus
    It's been a few months since I've touched Scheme and decided to implement a command line income partitioner using Scheme. My initial implementation used plain recursion over the continuation, but I figured a continuation would be more appropriate to this type of program. I would appreciate it if anyone (more skilled with Scheme than I) could take a look at this and suggest improvements. I'm that the multiple (display... lines is an ideal opportunity to use a macro as well (I just haven't gotten to macros yet). (define (ab-income) (call/cc (lambda (cc) (let ((out (display "Income: ")) (income (string->number (read-line)))) (cond ((<= income 600) (display (format "Please enter an amount greater than $600.00~n~n")) (cc (ab-income))) (else (let ((bills (* (/ 30 100) income)) (taxes (* (/ 20 100) income)) (savings (* (/ 10 100) income)) (checking (* (/ 40 100) income))) (display (format "~nDeduct for bills:---------------------- $~a~n" (real->decimal-string bills 2))) (display (format "Deduct for taxes:---------------------- $~a~n" (real->decimal-string taxes 2))) (display (format "Deduct for savings:-------------------- $~a~n" (real->decimal-string savings 2))) (display (format "Remainder for checking:---------------- $~a~n" (real->decimal-string checking 2)))))))))) Invoking (ab-income) asks for input and if anything below 600 is provided it (from my understanding) returns (ab-income) at the current-continuation. My first implementation (as I said earlier) used plain-jane recursion. It wasn't bad at all either but I figured every return call to (ab-income) if the value was below 600 kept expanding the function. (please correct me if that apprehension is incorrect!)

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  • Approaching SICP in Clojure instead of Scheme

    - by ironicaldiction
    I am a third year bachelor student in a software engineering program, and I brought up the idea of reading SICP to an adviser to gain a deeper and more fundamental understanding of the principles behind all this software we engineer. He suggested not to learn Scheme to complete the book (because it's not as common as modern dialects of Lisp) but to do the exercises in Clojure instead. It's an already difficult book, if I do attempt the book's exercises in the more modern Clojure, how would that work? For example, I can't find any real solutions, the syntax they teach for Scheme is different, etc.

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  • What should I learn from Scheme?

    - by bunglestink
    I was wondering what unique features I can learn from Scheme that would help me become a better programmer? I have a lot experience in mainstream languages, and I am looking to expand my horizons and learn about functional aspects that are missing from other languages. I am familiar with closures from javascript, lambda expressions from C#, and I was wondering what I can focus on that is lacking in other languages? Aside from the Lisp syntax, I feel like what I have seen so far I've already encountered in other languages. What is unique to Scheme/Lisp that will teach me something new?

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  • Am I getting Scheme wrong?

    - by nischayn22
    Inspired by the numerous posts about the importance of learning Lisp/Scheme I started to learn Scheme two days back, I am using the book "The little Schemer" and have completed half of it. But I still haven't learned anything new, the book teaches about recursion which I already understand and uses lambda (which I can think of a way to define a function in C). I still haven't got the concept of functional programming (please point to some example of functional compared to normal programming methods in C/C++ so I can get it). Am I learning in the wrong way? or is "The little Schemer" for a newbie in programming and I should look for some other books?

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  • Winner of the 2012 Government Big Data Solutions Award

    - by Jean-Pierre Dijcks
    Hot off the press: The winner of the 2012 Government Big Data Solutions Aware is the National Cancer Institute!! Read all the details on CTOLabs.com. A short excerpt to wet your appetite: "... This solution, based on the Oracle Big Data Appliance with the Cloudera Distribution of Apache Hadoop (CDH), leverages capabilities available from the Big Data community today in pioneering ways that can serve a broad range of researchers. The promising approach of this solution is repeatable across many other Big Data challenges for bioinfomatics, making this approach worthy of its selection as the 2012 Government Big Data Solution Award." Read the entire post. Congrats to the entire team!!

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  • The Oldest Big Data Problem: Parsing Human Language

    - by dan.mcclary
    There's a new whitepaper up on Oracle Technology Network which details the use of Digital Reasoning Systems' Synthesys software on Oracle Big Data Appliance.  Digital Reasoning's approach is inherently "big data friendly," as it leverages multiple components of the Hadoop ecosystem.  Moreover, the paper addresses the oldest big data problem of them all: extracting knowledge from human text.   You can find the paper here.   From the Executive Summary: There is a wealth of information to be extracted from natural language, but that extraction is challenging. The volume of human language we generate constitutes a natural Big Data problem, while its complexity and nuance requires a particular expertise to model and mine. In this paper we illustrate the impressive combination of Oracle Big Data Appliance and Digital Reasoning Synthesys software. The combination of Synthesys and Big Data Appliance makes it possible to analyze tens of millions of documents in a matter of hours. Moreover, this powerful combination achieves four times greater throughput than conducting the equivalent analysis on a much larger cloud-deployed Hadoop cluster.

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  • Scheme Beginner question

    - by Robert
    Hello.I am trying to put the following statement in Dr.Scheme: {with {x {+ 5 5}} {+ x x}} but I got an error: expand: unbound identifier in module in: with anyone could help me?Thanks.

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  • PLT Scheme URL dispatch

    - by Inaimathi
    I'm trying to hook up URL dispatch with PLT Scheme. I've taken a look at the tutorial and the server documentation. I can figure out how to route requests to the same servlets. Specific example: (define (start request) (blog-dispatch request)) (define-values (blog-dispatch blog-url) (dispatch-rules (("") list-posts) (("posts" (string-arg)) review-post) (("archive" (integer-arg) (integer-arg)) review-archive) (else list-posts))) (define (list-posts req) `(list-posts)) (define (review-post req p) `(review-post ,p)) (define (review-archive req y m) `(review-archive ,y ,m)) Assuming the above code running on a server listening 8080, localhost:8080/ goes to a page that says "list-posts". Going to localhost:8080/posts/test goes to a PLT "file not found" page (with the above code, I'd expect it to go to a page that says "review-post test"). It feels like I'm missing something small and obvious. Can anyone give me a hint?

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  • Big Data Accelerator

    - by Jean-Pierre Dijcks
    For everyone who does not regularly listen to earnings calls, Oracle's Q4 call was interesting (as it mostly is). One of the announcements in the call was the Big Data Accelerator from Oracle (Seeking Alpha link here - slightly tweaked for correctness shown below):  "The big data accelerator includes some of the standard open source software, HDFS, the file system and a number of other pieces, but also some Oracle components that we think can dramatically speed up the entire map-reduce process. And will be particularly attractive to Java programmers [...]. There are some interesting applications they do, ETL is one. Log processing is another. We're going to have a lot of those features, functions and pre-built applications in our big data accelerator."  Not much else we can say right now, more on this (and Big Data in general) at Openworld!

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  • Big Data – Buzz Words: What is HDFS – Day 8 of 21

    - by Pinal Dave
    In yesterday’s blog post we learned what is MapReduce. In this article we will take a quick look at one of the four most important buzz words which goes around Big Data – HDFS. What is HDFS ? HDFS stands for Hadoop Distributed File System and it is a primary storage system used by Hadoop. It provides high performance access to data across Hadoop clusters. It is usually deployed on low-cost commodity hardware. In commodity hardware deployment server failures are very common. Due to the same reason HDFS is built to have high fault tolerance. The data transfer rate between compute nodes in HDFS is very high, which leads to reduced risk of failure. HDFS creates smaller pieces of the big data and distributes it on different nodes. It also copies each smaller piece to multiple times on different nodes. Hence when any node with the data crashes the system is automatically able to use the data from a different node and continue the process. This is the key feature of the HDFS system. Architecture of HDFS The architecture of the HDFS is master/slave architecture. An HDFS cluster always consists of single NameNode. This single NameNode is a master server and it manages the file system as well regulates access to various files. In additional to NameNode there are multiple DataNodes. There is always one DataNode for each data server. In HDFS a big file is split into one or more blocks and those blocks are stored in a set of DataNodes. The primary task of the NameNode is to open, close or rename files and directory and regulate access to the file system, whereas the primary task of the DataNode is read and write to the file systems. DataNode is also responsible for the creation, deletion or replication of the data based on the instruction from NameNode. In reality, NameNode and DataNode are software designed to run on commodity machine build in Java language. Visual Representation of HDFS Architecture Let us understand how HDFS works with the help of the diagram. Client APP or HDFS Client connects to NameSpace as well as DataNode. Client App access to the DataNode is regulated by NameSpace Node. NameSpace Node allows Client App to connect to the DataNode based by allowing the connection to the DataNode directly. A big data file is divided into multiple data blocks (let us assume that those data chunks are A,B,C and D. Client App will later on write data blocks directly to the DataNode. Client App does not have to directly write to all the node. It just has to write to any one of the node and NameNode will decide on which other DataNode it will have to replicate the data. In our example Client App directly writes to DataNode 1 and detained 3. However, data chunks are automatically replicated to other nodes. All the information like in which DataNode which data block is placed is written back to NameNode. High Availability During Disaster Now as multiple DataNode have same data blocks in the case of any DataNode which faces the disaster, the entire process will continue as other DataNode will assume the role to serve the specific data block which was on the failed node. This system provides very high tolerance to disaster and provides high availability. If you notice there is only single NameNode in our architecture. If that node fails our entire Hadoop Application will stop performing as it is a single node where we store all the metadata. As this node is very critical, it is usually replicated on another clustered as well as on another data rack. Though, that replicated node is not operational in architecture, it has all the necessary data to perform the task of the NameNode in the case of the NameNode fails. The entire Hadoop architecture is built to function smoothly even there are node failures or hardware malfunction. It is built on the simple concept that data is so big it is impossible to have come up with a single piece of the hardware which can manage it properly. We need lots of commodity (cheap) hardware to manage our big data and hardware failure is part of the commodity servers. To reduce the impact of hardware failure Hadoop architecture is built to overcome the limitation of the non-functioning hardware. Tomorrow In tomorrow’s blog post we will discuss the importance of the relational database in Big Data. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Big Data, PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL

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  • Big Data Learning Resources

    - by Lara Rubbelke
    I have recently had several requests from people asking for resources to learn about Big Data and Hadoop. Below is a list of resources that I typically recommend. I'll update this list as I find more resources. Let's crowdsource this... Tell me your favorite resources and I'll get them on the list! Books and Whitepapers Planning for Big Data Free e-book Great primer on the general Big Data space. This is always my recommendation for people who are new to Big Data and are trying to understand it....(read more)

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  • E-Book on big data (featuring Analysts, Customers and more)

    - by Jean-Pierre Dijcks
    As we are gearing up for Openworld, here is a nice E-book on big data to start paging through. It contains Gartner's take on big data, customer and partner interviews and a lot more good info. Enjoy the read so you come prepared for Openworld!! Read the E-Book here. For those coming to Oracle Openworld (or the Americas Cup races around the same time), you can find big data sessions via this URL. Enjoy!!

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  • Scheme Depth-first search of a graph function

    - by John Retallack
    This is a homework question,I'm trying to do a Depth-first search function in Scheme,Here's the code I've written so far: (define explore (?(node visited) (let* ([neighbors (force (cdr node))] [next (nextNode visited neighbors)] [is-visited (member? node visited)]) (cond ;if I have no unvisited neighbours print current node and go up one level [(equal? next #f) (begin (display (car node)) (display " "))] ;if current node is not visited and I have unvisited neighbors ;print current node,mark as visited and visit it's neighbors [(and (equal? is-visited #f) (not (equal? next #f))) (begin (display (car node)) (display " ") (explore next (cons node visited)))]) ;go and visit the next neighbor (if (not (equal? (nextNode (cons next visited) neighbors) #f )) (explore (nextNode (cons next visited) neighbors) (cons node visited)))))) 'node' is the current node 'visited' is a list in witch I keep track of the nodes I visited 'nextNode' is a function that returns the first unvisited neighbor if any or #f otherwise 'member?' test's if a node is in the visited list The Graph representation is using adjacent made using references to nodes with letrec so that's why I use force in 'neighbors': Eg: (letrec ([node1 (list "NY" (delay (list node2 node3)))],where node2 and node3 are defined as node1 The problem witch I'm dealing with is that my visited lists looses track of some of the nodes I visited when I come out of recursion,How can I fix this ?

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  • How to bind "rest" variables to list of values in macro in Scheme

    - by Slartibartfast
    I want to make a helper macro for writing match-extensions. I have something like this: (define-match-expander my-expander (? (stx) (let* ([dat (cdr (syntax-e stx))] [var1 (car dat))] [var2 (cadr dat)]) ;transformer goes here ))) So I wanted a macro that will do this let binding. I've started with something like this: (define-syntax-rule (define-my-expander (id vars ...) body) (define-match-expander id (? (stx) (match-let ([(vars ...) (cdr (syntax-e stx))]) body)))) but match-let isn't defined in transformation time. First question would be is there any other way of doing this (making this expanders, I mean)? Maybe there is already something similar in plt-scheme that I'm not aware of, or I'm doing it wrong in some way. Regardless of answer on the first question, if I ever want to bound list of variables to list of values inside of a macro, how should I do it? EDIT: In combination with Eli's answer macro now looks like this: (define-syntax-rule (define-my-expander (id vars ...) body) (define-match-expander id (? (stx) (syntax-case stx () [(_ vars ...) body]))))

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  • Methods and properties in scheme - is object oriented programming possible in scheme?

    - by incrediman
    I will use a simple example to illustrate my question. In Java, C, or any other OOP language, I could create a pie class in a way similar to this: class Apple{ public String flavor; public int pieces; private int tastiness; public goodness(){ return tastiness*pieces; } } What's the best way to do that with Scheme? I suppose I could do with something like this: (define make-pie (lambda (flavor pieces tastiness) (list flavor pieces tastiness))) (define pie-goodness (lambda (pie) (* (list-ref pie 1) (list-ref pie 2)))) (pie-goodness (make-pie 'cherry 2 5)) ;output: 10 ...where cherry is the flavor, 2 is the pieces, and 5 is the tastiness. However then there's no type-safety or visibility, and everything's just shoved in an unlabeled list. How can I improve that? Sidenote: The make-pie procedure expects 3 arguments. If I want to make some of them optional (like I'd be able to in curly-brace languages like Java or C), is it good practice to just take the arguments in as a list (that is treat the arguments as a list - not require one argument which is a list) and deal with them that way?

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  • Scheme Formatting Help

    - by Logan
    I've been working on a project for school that takes functions from a class file and turns them into object/classes. The assignment is all about object oriented programming in scheme. My problem however is that my code doesn't format right. The output it gives me whenever I give it a file to pass in wraps the methods of the class in a list, making it so that the class never really gets declared. I can't for the life of me figure out how to get the parenthesis wrapping the method list to remove. I would really appreciate any help. Below is the code and the class file. ;;;; PART1 --- A super-easy set of classes. Just models points and lines. Tests all of the ;; basics of class behavior without touching on anything particularly complex. (class pointInstance (parent:) (constructor_args:) (ivars: (myx 1) (myy 2)) (methods: (getx () myx) (gety () myy) (setx (x) (set! myx x)) (show () (begin (display "[") (display myx) (display ",") (display myy) (display "]"))) )) (require (lib "trace.ss")) ;; Continue reading until you hit the end of the file, all the while ;; building a list with the contents (define load-file (lambda (port) (let ((rec (read port))) (if (eof-object? rec) '() (cons rec (load-file port)))))) ;; Open a port based on a file name using open-input-file (define (load fname) (let ((fport (open-input-file fname))) (load-file fport))) ;(define lis (load "C:\\Users\\Logan\\Desktop\\simpletest.txt")) ;(define lis (load "C:\\Users\\Logan\\Desktop\\complextest.txt")) (define lis (load "C:\\Users\\Logan\\Desktop\\pointinstance.txt")) ;(display (cdaddr (cdddar lis))) (define makeMethodList (lambda (listToMake retList) ;(display listToMake) (cond [(null? listToMake) retList ;(display "The list passed in to parse was null") ] [else (makeMethodList (cdr listToMake) (append retList (list (getMethodLine listToMake)))) ] ) )) ;(trace makeMethodList) ;this works provided you just pass in the function line (define getMethodLine (lambda (functionList) `((eq? (car msg) ,(caar functionList)) ,(caddar functionList)))) (define load-classes (lambda paramList (cond [(null? paramList) (display "Your parameters are null, man.")] [(null? (car paramList))(display "Done creating class definitions.")] [(not (null? (car paramList))) (begin (let* ((className (cadaar paramList)) (classInstanceVars (cdaddr (cddaar paramList))) (classMethodList (cdr (cadddr (cddaar paramList)))) (desiredMethodList (makeMethodList classMethodList '())) ) ;(display "Classname: ") ;(display className) ;(newline)(newline) ;(display "Class Instance Vars: ") ;(display classInstanceVars) ;(newline)(newline) ;(display "Class Method List: ") ;(display classMethodList) ;(newline) ;(display "Desired Method List: ") ;(display desiredMethodList)) ;(newline)(newline) ;---------------------------------------------------- ;do not delete the below code!` `(define ,className (let ,classInstanceVars (lambda msg ;return the function list here (cond ,(makeMethodList classMethodList '()))) )) ;--------------------------------------------------- ))] ) )) (load-classes lis) ;(load-classes lis) ;(load-classes-helper lis) ;(load-classes "simpletest.txt") ;(load-classes "complextest.txt") ;method list ;(display (cdr (cadddr (cddaar <class>))))

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  • "Final" Scheme REPL definitions: how to save them?

    - by Aeneas
    Is there a way to show and save all "final" definitions entered into a Scheme REPL into a text file? Say, if I have defined in the REPL: (define (increase x) (+ 1 x)) (define (multbytwo x) (* 3 x)) ; let us say this was an error (define (multbytwo x) (* 2 x)) I want to save this into an .scm-file with the content: (define (increase x) (+ 1 x)) (define (multbytwo x) (* 2 x)) i.e. the multbytwo function that got defined erraneously shall be "forgotten" due to re-definition. Is this possible?

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  • how to save and load the state of a game in scheme

    - by user3667664
    I'm creating the game of chess in scheme, but do not know how to save and load game state is a part I have this code (define-struct ficha(color se-movio? tipo-ficha )) ;;tablero lista de listas de fichas (define-struct estado (tablero turno fichaSel)) (define bpawn (bitmap "b-peon.png")) (define brook (bitmap "b-torre.png")) (define bcaballo (bitmap "b-caballo.png")) (define bbish (bitmap "b-arfil.png")) (define bquee (bitmap "b-reina.png")) (define bking (bitmap "b-rey.png")) (define wpawn (bitmap "w-peon.png")) (define wrook (bitmap "w-torre.png")) (define wcaballo (bitmap "w-caballo.png")) (define wbish (bitmap "w-arfil.png")) (define wquee (bitmap "w-reina.png")) (define wking (bitmap "w-rey.png")) (define board (bitmap "board.jpg")) This is the board that is a list of lists (define tableroini (list (list torreb caballob arfilb reinab reyb arfilb caballob torreb) (list peonb peonb peonb peonb peonb peonb peonb peonb) (list empty empty empty empty empty empty empty empty) (list empty empty empty empty empty empty empty empty) (list empty empty empty empty empty empty empty empty) (list empty empty empty empty empty empty empty empty) (list peonw peonw peonw peonw peonw peonw peonw peonw) (list torrew caballow arfilw reinaw reyw arfilw caballow torrew))) I did this to save the state of the game: (define (Guardar-en-archivo archivo) (write-file (string-append Subcarpeta archivo ".txt") "game state" )) But not as you insert the game state on "game state" for me to save the game How I can do this ?

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  • Detecting EOF in a Binary File using Scheme

    - by yuguang
    (define (read-all-input) (local ((define line (bytes->list (read-bytes 4)))) (if (eof-object? line) empty (cons line (read-all-input))))) (void (read-all-input)) The above code fails because bytes-list expects an argument of type byte string, but is given #

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  • Binary Trees in Scheme

    - by Javier
    Consider the following BNF defining trees of numbers. Notice that a tree can either be a leaf, a node-1 with one subtrees, or a node-2 with two subtrees. tree ::= (’leaf number) | (’node-1 tree) | (’node-2 tree tree) a. Write a template for recursive procedures on these trees. b. Define the procedure (leaf-count t) that returns the number of leaves in t > (leaf-count ’(leaf 5)) 1 > (leaf-count ’(node-2 (leaf 25) (leaf 17))) 2 > (leaf-count ’(node-1 (node-2 (leaf 4) (node-2 (leaf 2) (leaf 3))))) 3 Here's what I have so far: ;define what a leaf, node-1, and node-2 is (define leaf list) (define node-1 list) (define node-2 list) ;procedure to decide if a list is a leaf or a node (define (leaf? tree) (number? (car tree))) (define (node? tree) (pair? (car tree))) (define (leaf-count tree) (cond ((null? tree) 0) ((number? tree) 0) ((leaf? tree) 1) (else (+ (leaf-count (car tree)) (leaf-count (cdr tree)))))) It looks like it should run just fine, but when I try to run it using a simple test case like (leaf-count '(leaf 5)) I get the following error message: car: expects argument of type pair; given leaf What does this error message mean? I am defining a leaf as a list. But for some reason, it's not seeing that and gives me that error message.

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  • Matrix addition in Scheme

    - by user285012
    I am trying to add a matrix and it is not working... (define (matrix-matrix-add a b) (map (lambda (row) (row-matrix-add row b)) a)) (define (row-matrix-add row matrix) (if (null? (car matrix)) '() (cons (add-m row (map car matrix)) (row-matrix-add row (map cdr matrix))))) (define (add-m row col) (if (null? col) 0 (+ (car row) (car col) (add-m (cdr row) (cdr col)))))

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