Всем привет, есть вот такой файл, нужно в месте где написано КОД ПРОГРАММЫ написать тело функции until , которая проверяет переданное условие и если оно false выполняет действие и вызывает саму себя, если true выходит
Изначальное задание добавить until в ядро интерпретатора racket
Код:
#lang racket
;;
;; eval.scm - 6.037
;;
(require r5rs)
(define first car)
(define second cadr)
(define third caddr)
(define fourth cadddr)
(define rest cdr)
;; Tell DrRacket to print mutable pairs using the compact syntax for
;; ordinary pairs.
(print-as-expression #f)
(print-mpair-curly-braces #f)
;; mutable cons cell version of map
(define (mmap f lst)
(if (null? lst)
'()
(cons (f (car lst)) (mmap f (cdr lst)))))
(define (tagged-list? exp tag)
(and (pair? exp) (eq? (car exp) tag)))
(define (self-evaluating? exp)
(cond ((number? exp) #t)
((string? exp) #t)
((boolean? exp) #t)
(else #f)))
(define (quoted? exp) (tagged-list? exp 'quote))
(define (text-of-quotation exp) (cadr exp))
(define (variable? exp) (symbol? exp))
(define (assignment? exp) (tagged-list? exp 'set!))
(define (assignment-variable exp) (cadr exp))
(define (assignment-value exp) (caddr exp))
(define (make-assignment var expr)
(list 'set! var expr))
(define (definition? exp) (tagged-list? exp 'define))
(define (definition-variable exp)
(if (symbol? (cadr exp)) (cadr exp) (caadr exp)))
(define (definition-value exp)
(if (symbol? (cadr exp))
(caddr exp)
(make-lambda (cdadr exp) (cddr exp)))) ; formal params, body
(define (make-define var expr)
(list 'define var expr))
(define (lambda? exp) (tagged-list? exp 'lambda))
(define (lambda-parameters lambda-exp) (cadr lambda-exp))
(define (lambda-body lambda-exp) (cddr lambda-exp))
(define (make-lambda parms body) (cons 'lambda (cons parms body)))
(define (if? exp) (tagged-list? exp 'if))
(define (if-predicate exp) (cadr exp))
(define (if-consequent exp) (caddr exp))
(define (if-alternative exp) (cadddr exp))
(define (make-if pred conseq alt) (list 'if pred conseq alt))
(define (cond? exp) (tagged-list? exp 'cond))
(define (cond-clauses exp) (cdr exp))
(define first-cond-clause car)
(define rest-cond-clauses cdr)
(define (make-cond seq) (cons 'cond seq))
(define (let? expr) (tagged-list? expr 'let))
(define (let-bound-variables expr) (mmap first (second expr)))
(define (let-values expr) (mmap second (second expr)))
(define (let-body expr) (cddr expr)) ;differs from lecture--body may be a sequence
(define (make-let bindings body)
(cons 'let (cons bindings body)))
(define (begin? exp) (tagged-list? exp 'begin))
(define (begin-actions begin-exp) (cdr begin-exp))
(define (last-exp? seq) (null? (cdr seq)))
(define (first-exp seq) (car seq))
(define (rest-exps seq) (cdr seq))
(define (sequence->exp seq)
(cond ((null? seq) seq)
((last-exp? seq) (first-exp seq))
(else (make-begin seq))))
(define (make-begin exp) (cons 'begin exp))
(define (application? exp) (pair? exp))
(define (operator app) (car app))
(define (operands app) (cdr app))
(define (no-operands? args) (null? args))
(define (first-operand args) (car args))
(define (rest-operands args) (cdr args))
(define (make-application rator rands)
(cons rator rands))
(define (time? exp) (tagged-list? exp 'time))
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
(define (until? exp) (tagged-list? exp 'until))
(define (until-cond exp) (cadr exp))
(define (until-body exp) (cddr exp))
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;
;; this section is the actual implementation of meval
;;
(define (m-eval exp env)
(cond ((self-evaluating? exp) exp)
((variable? exp) (lookup-variable-value exp env))
((quoted? exp) (text-of-quotation exp))
((assignment? exp) (eval-assignment exp env))
((definition? exp) (eval-definition exp env))
((if? exp) (eval-if exp env))
((lambda? exp)
(make-procedure (lambda-parameters exp) (lambda-body exp) env))
((begin? exp) (eval-sequence (begin-actions exp) env))
((cond? exp) (m-eval (cond->if exp) env))
((let? exp) (m-eval (let->application exp) env))
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
((until? exp) (m-eval (until exp) env))
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
((time? exp) (time (m-eval (second exp) env)))
((application? exp)
(m-apply (m-eval (operator exp) env)
(list-of-values (operands exp) env)))
(else (error "Unknown expression type -- EVAL" exp))))
(define (m-apply procedure arguments)
(cond ((primitive-procedure? procedure)
(apply-primitive-procedure procedure arguments))
((compound-procedure? procedure)
(eval-sequence
(procedure-body procedure)
(extend-environment (make-frame (procedure-parameters procedure)
arguments)
(procedure-environment procedure))))
(else (error "Unknown procedure type -- APPLY" procedure))))
(define (list-of-values exps env)
(cond ((no-operands? exps) '())
(else (cons (m-eval (first-operand exps) env)
(list-of-values (rest-operands exps) env)))))
(define (eval-if exp env)
(if (m-eval (if-predicate exp) env)
(m-eval (if-consequent exp) env)
(m-eval (if-alternative exp) env)
))
(define (eval-sequence exps env)
(cond ((last-exp? exps) (m-eval (first-exp exps) env))
(else (m-eval (first-exp exps) env)
(eval-sequence (rest-exps exps) env))))
(define (eval-assignment exp env)
(set-variable-value! (assignment-variable exp)
(m-eval (assignment-value exp) env)
env))
(define (eval-definition exp env)
(define-variable! (definition-variable exp)
(m-eval (definition-value exp) env)
env))
(define (let->application expr)
(let ((names (let-bound-variables expr))
(values (let-values expr))
(body (let-body expr)))
(make-application (make-lambda names body)
values)))
(define (cond->if expr)
(let ((clauses (cond-clauses expr)))
(if (null? clauses)
#f
(if (eq? (car (first-cond-clause clauses)) 'else)
(sequence->exp (cdr (first-cond-clause clauses)))
(make-if (car (first-cond-clause clauses))
(sequence->exp (cdr (first-cond-clause clauses)))
(make-cond (rest-cond-clauses clauses)))))))
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
(define (until exp)
(КОД_ПРОГРАММЫ))
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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