problem about racket-Collection of common programming errors

  • Will Ness
    scheme racket
    I’m trying to write some code, but there is a problem with my reply procedure. Ignore the procedures for the first two random-of-threes, but the problem is in the else when calling the pick-random procedure. Here’s the code:(define earlier-responses ‘()) (define (doctor-driver-loop name earlier-

  • Keen
    functional-programming scheme racket mutable
    i have this definition “sort left list” which is a list of pairs sorted according to the left element of each pair the left element must be a non-negative integer and the right component may be a value of any typei have to

  • Timbo925
    table user-interface listbox scheme racket
    I’m currently trying to create a a grid of information in Racket using the Racket Graphical Interface Tooling. The only real table that is available is the list-box% (link to reference)To fill the table I need to use:(send a-list-box set choices …) → void?choices : (listof label-string?)choices being list being a list of each column. The problem is that I have a variable amount of collumns. My current data is formated like (list (list 1 2 3) (list 4 5 6))

  • Yasir Arsanukaev
    list scheme racket
    Below is my code which takes a car element of a list(carVal) and an list(initialized to

  • Óscar López
    scope scheme racket define
    I need some function which among other stuff would define a new global symbol. So that I could use it like this:(define (func-prototype symbol value comment)(define symbol value) ; th

  • Chris Jester-Young
    racket cartesian-product
    I was hoping someone could guide me in the right direction: I am looking two produce all possible combinations of items in two lists: Example: Given the lists ‘(symbo

  • mac01021
    lisp scheme racket
    Using DrRacket, on both linux and Mac OS, the following code gives this error *: expects type as 1st argument, given #but if I uncomment the (newline) at the beginning of the procedu

  • Michael McGuinness
    scheme racket
    I have been trying to launch a racket program from the commandline (via ‘racket’) but have not been having success. According to the documentation (here

  • akavel
    scheme racket old historical
    I’m trying to resurrect an old (1999 or earlier) project written in Scheme (PLT-Scheme, using the mzscheme interpreter (?) commandline tool). To make the matters worse, I don’t know Scheme, or Lisp (in fact, I want to learn, but that’s another story).I have the source code of the project at:, when running the code, it bails out with an error message like below:Sherman runtime version 0.5 Hosted on MzScheme version 52, Copyright (c) 1995-98 PLT (Matthew Flatt) reference to undefined identifier: list->block

  • Yasir Arsanukaev
    recursion racket
    I’m still plugging away at the exercises in How to Design Programs on my own, but have managed to get stuck again. This time it’s question 11.4.7:Develop the functionis-not-divisible-by=1], i, and a naturalnumber m, with i < m. If m is notdivisible by any number between 1(exclusive) and i (inclusive), thefunction produces true; otherw

  • Eli Barzilay
    scheme eval racket
    The following racket function produces the error:reference to undefined identifier: valThis i

  • ecounysis

  • user2085086
    scheme racket scoping drracket
    So I know that in Scheme define is for dynamic scoping and let for static scoping, yet the following thing confuses me:If I have(let ((x 0))(define f (lambda () x))(display (f))(let ((x 1))(displa

  • Sam Tobin-Hochstadt
    When building up some functions, I can make some mistakes. When

  • Eli Barzilay
    scheme racket
    Hey i’m just trying to write some code in DrScheme: ((function (

  • Sam Tobin-Hochstadt
    lisp scheme racket
    I’m trying to run the program described in SICP 4.1 ( but have run into some difficulty in redefining the function apply as the book suggests that you do. The code is the following:#lang planet neil/sicp;; —————————————————————————– ;; 4.1.1 The Core of the Evaluator ;; —————————————————————————–;; Eval (define apply-in-underlying-scheme apply) (define (eval exp env)(display ‘eval)(newline)(display exp)(newline)(cond ((self-evaluating? exp) exp)((variable? exp) (let ((res (lookup-variable-value exp env)))(display (list ‘lookup exp))(newline)(display res)(newline)res))((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 “Unknown expression” exp))));; Apply(define (apply procedure arguments)(display ‘apply)(newline)(display procedure)(newline)(cond ((primitive-procedure? procedure)(apply-primitive-procedure procedure arguments))((compound-procedure? procedure)(eval-sequence(procedure-body procedure)(extend-environment(procedure-parameters procedure)arguments(procedure-environment procedure))))(else(error”Unknown procedure type — ” procedure))));; Application(define (application? exp) (pair? exp)) (define (operator exp) (car exp)) (define (operands exp) (cdr exp));; Procedure arguments(define (list-of-values exps env)(if (no-operands? exps)'()(cons (eval (first-operand exps) env)(list-of-values (rest-operands exps) env))))(define (no-operands? ops) (null? ops)) (define (first-operand ops) (car ops)) (define (rest-operands ops) (cdr ops));; Conditionals(define (eval-if exp env)(if (true? (eval (if-predicate exp) env))(eval (if-consequent exp) env)(eval (if-alternative exp) env)));; Sequences(define (eval-sequence exps env)(cond ((last-exp? exps) (eval (first-exp exps) env))(else (eval (first-exp exps) env)(eval-sequence (rest-exps exps) env))));; Assignments and definitions(define (eval-assignment exp env)(set-variable-value! (assignment-variable e

  • Gilles
    variables scheme racket
    I think I read somewhere that you could bind multiple definitions to a single name in scheme. I know I might be usin

  • Chris Jester-Young
    scheme racket continuations
    Consider the following code:(call-with-values(lambda ()(call/cc (lambda (k)(k k k))))(lambda (x y)(procedure-arity y)))It’s pretty obvious here that the continuation at the point of the call/cc call is the lambda on the right-hand side, so its ari

  • Nathan Campos
    regex url racket
    I’m trying to use the URL regular expression to match URLs in Racket like this:(regexp-match #rx”((mailto\:|(news|(ht|

Originally posted 2013-11-09 23:20:22.