r5rs

问题 I love DrRacket IDE, but currently I'm building a pet project where I would like to be independent from it, meaning i'm commited to use only R5RS standard procedures. The thing is, in DrRacket there's this procedure called "error" which i would like to continue using but I can't find it in the Standards. What i would like to know is if there's a way to emulate that "error" procedure using only the Standards procedures so that the code is portable between different implementations of Scheme. I

问题 I've written a piece of code, which creates a vector 'scoreboard' that contains 3 seperate vectors of size 3, all containing the symbol ? at all indices 0-2. When i now execute a 'vector-set!' on the first vector of scoreboard, to change its first element to a 'X, vectors 2 and 3 will change too. How does this occur? (define scoreboard (make-vector 3 (make-vector 3 '?))) (define (display-scoreboard) (display (vector-ref scoreboard 0)) (newline) (display (vector-ref scoreboard 1)) (newline)

问题 I've written a piece of code, which creates a vector 'scoreboard' that contains 3 seperate vectors of size 3, all containing the symbol ? at all indices 0-2. When i now execute a 'vector-set!' on the first vector of scoreboard, to change its first element to a 'X, vectors 2 and 3 will change too. How does this occur? (define scoreboard (make-vector 3 (make-vector 3 '?))) (define (display-scoreboard) (display (vector-ref scoreboard 0)) (newline) (display (vector-ref scoreboard 1)) (newline)

问题 I've written a piece of code, which creates a vector 'scoreboard' that contains 3 seperate vectors of size 3, all containing the symbol ? at all indices 0-2. When i now execute a 'vector-set!' on the first vector of scoreboard, to change its first element to a 'X, vectors 2 and 3 will change too. How does this occur? (define scoreboard (make-vector 3 (make-vector 3 '?))) (define (display-scoreboard) (display (vector-ref scoreboard 0)) (newline) (display (vector-ref scoreboard 1)) (newline)

问题 I've written a piece of code, which creates a vector 'scoreboard' that contains 3 seperate vectors of size 3, all containing the symbol ? at all indices 0-2. When i now execute a 'vector-set!' on the first vector of scoreboard, to change its first element to a 'X, vectors 2 and 3 will change too. How does this occur? (define scoreboard (make-vector 3 (make-vector 3 '?))) (define (display-scoreboard) (display (vector-ref scoreboard 0)) (newline) (display (vector-ref scoreboard 1)) (newline)

问题 I'm working on sorting a list of lists by their first element for example (sort (list '(2 1 6 7) '(4 3 1 2 4 5) '(1 1)))) expected output => ('(1 1) '(2 1 6 7) '(4 3 1 2 4 5)) The algorithm I used is bubble sort. And I modified it to deal with lists. However, the code doesn't compile. The error is mcar: contract violation expected: mpair? given: 4 Can someone correct my code and explain it. Thank you (define (bubble L) (if (null? (cdr L)) L (if (< (car (car L)) (car (cadr L))) (list (car L)

问题 Closed. This question needs debugging details. It is not currently accepting answers. Want to improve this question? Update the question so it's on-topic for Stack Overflow. Closed 2 days ago . I am trying to write a function, (codeWords t) , which traverses a Huffman tree (adds #\0 when it goes left, adds #\1 when it goes right...) and returns these values in pairs of the symbol at a leaf along with its associated encoding as a string over the characters #\0 and #\1 . Similar to what this or

问题 In DrRacket IDE, I was able to get the system date in the following manner when the language setting was 'Swindle': (define currentMonth 0) (let ((date (seconds->date (current-seconds)))) (set! currentMonth (date-month date)) ) Now, I need to do the same in R5Rs, but not sure how to. May I please seek your advise/help on this.. Thank you! 回答1: There is no date-time support in R5RS. The procedures current-seconds , seconds->date and date-month should be available in the R5RS implementation of

问题 I'm curious about the return value of define in Scheme. So I wrote the following lines in Racket #lang r5rs (display (define a 3)) And get the error define: not allowed in an expression context in: (define a 3) I have 2 questions about this: Does it mean that define has no return value? According to R5RS, define is not an expression. It's a program structure. Is it true that only expressions have return values, and other forms don't? 回答1: "If a tree falls in a forest and no one is around to

问题 I want to write my own append , for appending an element to an existing list . I've written the following : (define (appendElem llist elem) (if (null? llist) elem (cons (car llist) (appendElem (cdr llist) elem)))) But when I do this : (appendElem (list 1 2 30) 11) I get : (1 2 30 . 11) So the question is , why (1 2 30 . 11) and not (1 2 30 11) ? Thanks EDIT: Fixed : (define (appendElem llist elem) (if (null? llist) (list elem) (cons (car llist) (appendElem (cdr llist) elem)))) 回答1: Think