lisp

问题 Morning - I'm trying to see if there is a way to check if an item returned from a list is a list itself. For example (elt '(a (b c) d) 1) Is there a way to check that the item returned is a list? I tried using length, (length (elt '(a (b c) d) 1)) but if it is given an item that is not a list it throws an error. In short I'm looking for a way to go through each element of a list and check if it is a list or not. Thank you 回答1: the listp tells you that : (listp (elt '(a (b c) d) 1)) 来源： https:

问题 I'm having a bit of a struggle with coding a procedure that flattens a list once, i.e (flatten-once '((b) (c f) ((d)(e)))) would produce '(b c f (d) (e))) . I checked up on a few sources on how the standard flatten procedure works but it implements functions that are not included in the intermediate student with lambda language form I'm required to use. As far as I have it figured out a foldr would be somewhat helpful and have managed to get this (define (flatten-once lst) (cond [(empty? lst)

问题 I'm running the teapot example from cl-opengl package. The only changes I've made are loading the required packages. It works fine when executed from unix shell ( sbcl --load "3.cl" ), but when I try to compile and load it through SLIME ( C-c C-k ) i get the error about package GLUT not found. Curiously, the compiler chokes on the (defclass glut-teapot-window (glut:window) . What gives??? Here's a screenshot of what happens Here's the code for 3.cl. ;;;; -*- Mode: lisp; indent-tabs-mode: nil

问题 Suppose I want to find out in which package a class is defined, e.g. say (defclass x ()()) is defined in p1. One way could be to get the package via (symbol-package 'x). the problem with this solution is that x is exported in a different package p2. Any other suggestions? 回答1: As Rainer Joswig said, classes aren't defined in packages; symbols have packages and the name of a class is a symbol. If you want to know the value of *PACKAGE* at the time the class definition read, compiled, or loaded

问题 How I could remove a sublist by searching only one elem from it. For example, let's have the list: ( (pacific (atlanta ohaio) (NY LI)) (atlanta (pacific blue) (ohaio green)) ) And I want to remove "pacific" from the list and to get: ( (pacific (atlanta ohaio) (NY LI)) (atlanta (ohaio green)) ) Any ideas would be greatly appreciated :). 回答1: The criteria for deleting an element from the input list is not stated clearly in the question. This will work for the example shown: (define lst '(

问题 I have basic scheme like lisp in JavaScript and have problem with backquote and quote macros, they evaluate symbols if they are at first element of the array like > `(foo 10) give error foo not found it work for code like this > (define x '(1 2 3)) > (print `(1 2 ,@x 4 5)) my eval function look like this: function evaluate(code, env) { env = env || global_env; var value; if (typeof code === 'undefined') { return; } var first = code.car; var rest = code.cdr; if (first instanceof Pair) { value

问题 I'm struggling with the syntax for a function that zips together any number of lists. I currently have: (define (zip . [lsts : (Listof Any) *]) (apply map (inst list Any) lsts)) Which causes the following error when evaluated: Error: struct:exn:fail:syntax /Applications/Racket v6.6/collects/racket/private/kw.rkt:929:25: Type Checker: Bad arguments to function in `apply': Domains: (-> a b ... b c) (Listof a) (Listof b) ... b (-> a c) (Pairof a (Listof a)) Arguments: (-> Any * (Listof Any))

问题 Consider these two: (defparameter *lfn* (let ((count 0)) #'(lambda () (incf count)))) (defun testclosure () (let ((count 0)) #'(lambda () (incf count)))) Why do they behave differently: CL-USER> (funcall (testclosure)) 1 CL-USER> (funcall (testclosure)) 1 CL-USER> (funcall *lfn*) 1 CL-USER> (funcall *lfn*) 2 count is closed over in the defparameter version but not in the defun version. Why is this? 回答1: Sylwester's answer explains this very well, but in a case an example with more explicit

问题 i have a problem while loading my source file inside terminal using clisp. if i execute the following command to load the file: (load #p "filename.lisp") it gives me the following error: SYSTEM::LINE-COMMENT-READER: Invalid byte sequence #xE0 #xA0 #x20 in CHARSET:UTF-8 conversion can someone please tell me what i need to do in order to load the file? thank you. 回答1: Your file is encoded with ISO-8859-1: $ file filename.lisp filename.lisp: ISO-8859 text, with no line terminators Based on CLISP

问题 (This is a CS-theory type of question; I hope that's acceptable.) The "Lisp-1 vs Lisp-2" debate is about whether the namespace of functions should be distinct from the namespace of all other variables, and it's relevant in dynamically typed languages that allow the programmer to pass around functions as values. Lisp-1 languages (such as Scheme) have one namespace, so you can't have both a function named f and also an integer named f (one would shadow the other, just like two integers named f