lisp

判断语句 在Clojure中，所有的语法规则最终都是S表达式。我们如何知道哪些是判断语句呢？这个很简单，clojure中（lisp习惯）有个规定：对于判断功能的函数，函数名后面都有一个“？”号。所以我们只要看到后面带问号的函数名，就知道这一定是一个判断语句。很简单吧！ 例如 "fn?"这个函数用于判断传入的参数是否是一个函数： =>(fn? reduce) true =>(fn? 42) false 基本类型 数字（Number） Clojure支持非常丰富的数字类型的数据。每一种数字类型都提供了不同的计算精度，当然也占用不同的内存空间。当我们选择不同的数据类型时，精度、内存消耗这些因素对计算的性能和准确度有着至关重要的影响。所以我们必须对不同的数据类型有着深入的了解。 =>42 42 ;;整形 =>(class 42) java.lang.Integer ;;判断是否是数字 =>(number? 42) true ;;判断是否是整形 =>(integer? 42) true =>21.42 21.42 ;;查看类型 =>(class 21.42) java.lang.Double ;;判断是否是数字 =>(number? 21.42) true ;;判断是否是整形 =>(integer? 21.42) false 整形和浮点型在其他语言中都是常见的数据类型。但是分数（ratios

有时候，你可能需要防止一个表达式或者部分表达式被执行。这种就需要一种称为“代码保护”的技术。这项技术使用起来非常简单，就是在表达式前面加上一个单引号“ ‘ ”。clojure 遇到这种前缀加上单引号的表达式就会直接跳过求值，直接把其当做一种叫做“符号”的数据结构。 =>(+ 4 5 3) 12 =>'(+ 4 5 3) (+ 4 5 3) =>(str '(+ 4 5 3) " is protected while " (+ 4 5 3) " is evaluated.") "(+ 4 5 3) is protected while 12 is evaluated." 关于符号： 这里的单引号实际上是另一种形式，叫做quote。'(1 2 3)和(quoto (1 2 3))只是表示相同事物的不同方法而已。quote（或者单引号）可以在任何地方使用，来阻止Clojure立即对一个表达式求值。实际上，它的作用远不 止于声明一个列表，当涉及到元编程的时候，单引号十分必须。这个后面在对符号作用进行详细说明。 来源： oschina 链接： https://my.oschina.net/u/578710/blog/142297

现在我们首先定义一个支持4个参数相加的函数： (defn add [ v1 v2 v3 v4] (+ v1 v2 (if v3 v3 0) (if v4 v4 0) )) 我们想达到这样一种效果。如果我们调用(add 1 2 3 4)，则正常返回10。如果我们调用(add 1 2 3)能得到结果6。或者调用(add 1 2)能得到3。 我们执行后发现： => (add 1 2 3 4) 10 => (add 1 2) ... ArityException Wrong number of args (2) passed to: user$add ... 当参数数量和我们定义函数时的参数数量一致时能得到正确的值。否则会抛出参数数量不匹配异常。看来这个和我们预想的不一样啊。 固定参数 我们之前定义函数时，使用的都是固定参数方式。调用函数时，只要我们传入参数的数量不符合定义时的参数数量，clojure都会提出抗议（抛出参数数量不匹配异常）。像上面我们可以这么调用（add 1 2 3 nil),这样会返回6。 (if v4 v4 0)的含义是，如果v4 不为nil或false，就返回v4，否则返回0。我们传入的正是nil。所以函数会正确返回6。当然(add 1 2 nil nil )也会正确返回3。 难道clojure就这么点能力？当然不是，clojure的固定参数可不止这点能耐

i see several examples of implementing append an element to a list, but all are not using tail recursion . how to implement such a function in a functional style? (define (append-list lst elem) expr) The following is an implementation of tail recursion modulo cons optimization, resulting in a fully tail recursive code. It copies the input structure and then appends the new element to it, by mutation, in the top-down manner. Since this mutation is done to its internal freshly-created data, it is still functional on the outside (does not alter any data passed into it and has no observable

This question already has an answer here: How to modify this “make-matrix” function? 1 answer I'm trying to create a function that receives a number of lines and columns and makes an array out of it. This is what I did (defun create-table (lines columns) (make-array '(lines columns))) I thought this is how you make a multidimensional array. But as I call the function create-table for example (create-table 2 2) this error is given MAKE-ARRAY: dimension LINES is not of type `(INTEGER 0 (,ARRAY-DIMENSION-LIMIT)) I don't understand, how could it not be an integer? Should I make a cast? What do you

I want to read in the contents of a file into a list. Some of my attempts so far have been - (defun get-file (filename) (let ((x (open filename))) (when x (loop for line = (read-line x nil) while line do (list line))) (close x))) (defun get-file (filename) (let ((x (open filename :if-does-not-exist nil)) (contents (list nil))) (when x (loop for line = (read-line x nil) while line do (cons contents line))) (close x) contents)) (defun get-file (filename) (let ((x (open filename :if-does-not-exist nil)) (contents nil)) (when x (loop for line = (read-line x nil) while line do (append contents line

How can I remove nested parentheses recursively in Common LISP Such as (unnest '(a b c (d e) ((f) g))) => (a b c d e f g) (unnest '(a b)) => (a b) (unnest '(() ((((a)))) ())) => (a) Thanks Here's what I'd do: (ql:quickload "alexandria") (alexandria:flatten list) That works mainly because I have Quicklisp installed already. (defun flatten (l) (cond ((null l) nil) ((atom l) (list l)) (t (loop for a in l appending (flatten a))))) (defun flatten (l) (cond ((null l) nil) ((atom (car l)) (cons (car l) (flatten (cdr l)))) (t (append (flatten (car l)) (flatten (cdr l)))))) I realize this is an old