scheme

问题 How do I get a definition's name as a symbol in Scheme and/or Racket? Suppose I have these definitions: (define bananas 123) (define multiply *) (define (pythagoras a b) (sqrt (+ (* a a) (* b b)))) How can I define def->symbol where: (def->symbol bananas) returns 'bananas (def->symbol multiply) returns 'multiply (def->symbol pythagoras) returns 'pythagoras Is this a case where I have no choice but to learn and use these advanced things called "macros"? 回答1: Just as you suspect, we need to use

问题 Say I have this code: #lang racket (define a ((λ (x) x) ((λ (y) y) (λ (z) ((λ (w) w) z))))) I know intuitively that this lambda expression is (extensionally) equal to (λ (z) z) My question is if there is a way to print out the body of a in case I want to see how much the function got simplified internally by Racket. More information: By default, if I type a into the interpreter, I get #<procedure:y> (This seems to give a hint as to how much evaluation happened). I can change the output style

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'm writing a small interpreter for a C-like language in Scheme (R5RS) and trying to convert something like: for (i = 0; i < 100; i++) { if (isprime(i)) continue; else /* do something with i */ } to valid Scheme (the isprime function is just an example and not important). However, after trying for some time, I have not been able to find an efficient/simple way to add the equivalent of a continue statement to a do loop in Scheme. What would be even better would be a "for" macro which allows

问题 I'm writing a small interpreter for a C-like language in Scheme (R5RS) and trying to convert something like: for (i = 0; i < 100; i++) { if (isprime(i)) continue; else /* do something with i */ } to valid Scheme (the isprime function is just an example and not important). However, after trying for some time, I have not been able to find an efficient/simple way to add the equivalent of a continue statement to a do loop in Scheme. What would be even better would be a "for" macro which allows

问题 I want to create two process in Guile and send the output (stdout) from one of them as input (stdin) to the other. Using the following example, how can this be done? echo "foo bar" | wc Output: 1 2 8 回答1: Yes, you can do this using open-output-pipe : (let ((p (open-output-pipe "wc"))) (display "The quick brown fox jumps over the lazy dog.\n" p) (close-pipe p)) This is equivalent to echo "The quick brown fox jumps over the the lazy dog." | wc (including echo 's implicit newline because I'm

问题 I want to create two process in Guile and send the output (stdout) from one of them as input (stdin) to the other. Using the following example, how can this be done? echo "foo bar" | wc Output: 1 2 8 回答1: Yes, you can do this using open-output-pipe : (let ((p (open-output-pipe "wc"))) (display "The quick brown fox jumps over the lazy dog.\n" p) (close-pipe p)) This is equivalent to echo "The quick brown fox jumps over the the lazy dog." | wc (including echo 's implicit newline because I'm

问题 How can I pass a variable by reference in scheme? An example of the functionality I want: (define foo (lambda (&x) (set! x 5))) (define y 2) (foo y) (display y) ;outputs: 5 Also, is there a way to return by reference? 回答1: See http://community.schemewiki.org/?scheme-faq-language question "Is there a way to emulate call-by-reference?". In general I think that fights against scheme's functional nature so probably there is a better way to structure the program to make it more scheme-like. 回答2:

问题 I have one more questions about Hygienic macros in Scheme, consider example from R5RS (let-syntax ((when (syntax-rules () ((when test stmt1 stmt2 ...) (if test (begin stmt1 stmt2 ...)))))) (let ((if #t)) (when if (set! if 'now)) if)) Why it match if the pattern have 3 arguments and ellipsis that can match empty list? It's called with 2 arguments if and (set! if 'now) . What should be ... bind to, if stmt2 can be bind to empty list? This is kind of non Lispy if ... is just nothing. Is that

问题 I have one more questions about Hygienic macros in Scheme, consider example from R5RS (let-syntax ((when (syntax-rules () ((when test stmt1 stmt2 ...) (if test (begin stmt1 stmt2 ...)))))) (let ((if #t)) (when if (set! if 'now)) if)) Why it match if the pattern have 3 arguments and ellipsis that can match empty list? It's called with 2 arguments if and (set! if 'now) . What should be ... bind to, if stmt2 can be bind to empty list? This is kind of non Lispy if ... is just nothing. Is that