我想通读这本书:http://www.eecs.berkeley.edu/~bh/ss-toc2.html .但是我很难让“简单方案”语言工作。代码不会运行。
#lang planet dyoo/simply-scheme:2
(parse ’(4 + 3 * 7 - 5 / (3 + 4) + 6))
我不断收到以下错误消息:“解析:模块中的未绑定(bind)标识符:解析”。
最佳答案
看看这个page ,它有完整的说明。只需这样做:
#lang racket
(require (planet dyoo/simply-scheme:2:2))
另请注意
’
字符不正确,引用使用 '
,这可能是因为您复制粘贴的代码排版错误。当然,完成上述操作后,您还必须定义第 18 章中解释的程序,它们并没有在您刚刚导入的包中定义!这肯定会起作用:
(define (parse expr)
(parse-helper expr '() '()))
(define (parse-helper expr operators operands)
(cond ((null? expr)
(if (null? operators)
(car operands)
(handle-op '() operators operands)))
((number? (car expr))
(parse-helper (cdr expr)
operators
(cons (make-node (car expr) '()) operands)))
((list? (car expr))
(parse-helper (cdr expr)
operators
(cons (parse (car expr)) operands)))
(else (if (or (null? operators)
(> (precedence (car expr))
(precedence (car operators))))
(parse-helper (cdr expr)
(cons (car expr) operators)
operands)
(handle-op expr operators operands)))))
(define (handle-op expr operators operands)
(parse-helper expr
(cdr operators)
(cons (make-node (car operators)
(list (cadr operands) (car operands)))
(cddr operands))))
(define (precedence oper)
(if (member? oper '(+ -)) 1 2))
(define (compute tree)
(if (number? (datum tree))
(datum tree)
((function-named-by (datum tree))
(compute (car (children tree)))
(compute (cadr (children tree))))))
(define (function-named-by oper)
(cond ((equal? oper '+) +)
((equal? oper '-) -)
((equal? oper '*) *)
((equal? oper '/) /)
(else (error "no such operator as" oper))))
(parse '(4 + 3 * 7 - 5 / (3 + 4) + 6))
=> '(+ (- (+ (4) (* (3) (7))) (/ (5) (+ (3) (4)))) (6))
(compute (parse '(4 + 3 * 7 - 5 / (3 + 4) + 6)))
=> 30 2/7
关于scheme - 将 "Simply Scheme"语言添加到 DrRacket,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/19203498/