(sicp47)m4.1~4.2
いつやったかは忘れた。(upし忘れてた）
;;eval/applyは元の関数を覆い隠さない様に@をつけよう (define (@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) (@eval (cond->if exp) env)) ((application? exp) (@apply (@eval (operator exp) env) (list-of-values (operands exp) env))) (else (error "Unknown expression type -- EVAL" exp)))) (define (@apply procedure arguments) (cond ((primitive-procedure? procedure) (apply-primitive-procedure procedure arguments)) ((compound-procedure? procedure) (eval-sequence (procedure-body procedure) (extend-environment (procedure-parameters procedure) arguments (procedure-environment procedure)))) (else (error "Unknown procedure type -- APPLY" procedure)))) (define (list-of-values exps env) (if (no-operands? exps) '() (cons (@eval (first-operand exps) env) (list-of-values (rest-operands exps) env)))) ;;4.1 ;;letを使って先に計算すればいい。 (define (list-of-values-from-right exps env) (if (no-operands? exps) '() (let1 rest (list-of-values-from-right (rest-operands exps) env) (cons (@eval (first-operand exps) env) rest)))) (define (list-of-values-from-left exps env) (if (no-operands? exps) '() (let1 first (@eval (first-operand exps) env) (cons first (list-of-values-from-left (rest-operands exps) env))))) (define (true? condition) (eq? condition #t)) ;;(@eval (anything ... ) exp env)ってmacroにできるような気がする。 (define (eval-sequence exps env) (cond ((last-exp? exps) (@eval (first-exp exps) env)) (else (@eval (first-exp exps) env) (eval-sequence (rest-exps exps) env)))) (define (eval-if exp env) (if (true? (@eval (if-predicate exp) env)) (@eval (if-consequent exp) env) (@eval (if-alternative exp) env))) (define (eval-assignment exp env) (set-variable-value! (assignment-variable exp) (@eval (assignment-value exp) env) env) 'ok) (define (eval-definition exp env) (define-variable! (definition-variable exp) (@eval (definition-value exp) env) env) 'ok) (define (self-evaluating? exp) (cond ((number? exp) #t) ((string? exp) #t) (else #f))) (define (variable? exp) (symbol? exp)) (define (quoted? exp) (tagged-list? exp 'quote)) (define (tagged-list? exp tag) (if (pair? exp) (eq? (car exp) tag) false)) ;;--assignment-- (define (assignment exp) (tagged-list? exp 'set!)) (define (assignment-variable exp) (cadr exp)) (define (assignment-value exp) (caddr exp)) ;;--definition-- (define (definition? exp) (tagged-list? exp 'define)) ;; (define (definition? exp) (tagged-list? exp 'define)) ;; (define (<var> <parameter1> ... <parametern>) ;; <body>) ;; (define <var> ;; (lambda (<parameter1> ... <parametern>) ;; <body>)) (define (definition-variable exp) (if (symbol? (cadr exp)) (cadr exp) (caddr exp))) (define (definition-value exp) (if (symbol? (cadr exp)) (caddr exp) (make-lambda (caddr exp) (cddr exp)))) ;;--lambda-- (define (lambda? exp) (tagged-list? exp 'lambda)) ;;(lambda (par1 par2 ..) body) (define (lambda-parameters exp) (cadr exp)) (define (lambda-body exp) (cddr exp)) (define (make-lambda paramators body) (cons 'lambda (cons paramators body))) ;;--if-- (define (if? exp) (tagged-list? exp 'if)) ;;(if predicate consequent alternative) (define (if-predicate exp) (cadr exp)) (define (if-consequent exp) (caddr exp)) (define (if-alternative exp) (if (not (null? (cdddr exp))) (cadddr exp) #f)) (define (make-if predicate consequent alternative) (list 'if predicate consequent alternative)) ;;--begin-- (define (begin? exp) (tagged-list? exp 'begin)) (define (begin-actioin seq) (cdr seq)) (define (last-exp? seq) (null? (cdr seq))) (define (first-exp seq) (car seq)) (define (rest-exp seq) (cdr seq)) (define (sequence->exp seq) (cond ((null? seq) seq) ((last-exp? seq) (first-exp seq)) (else (make-begin seq)))) (define (make-begin seq) (cons 'begin seq)) ;;--application-- (define (application? exp) (pair? exp)) (define (operator exp) (car exp)) (define (operands exp) (cdr exp)) (define (no-operands? ops) (null? ops)) (define (first-operand ops) (car ops)) (define (rest-operands ops) (cdr ops)) ;;--cond (cond->if)-- (define (cond? exp) (tagged-list? exp 'cond)) ;;cond = (cond clauses) ;;clauses = (list clause1 clause2 ...) (define (cond-clauses exp) (cdr exp)) ;;clause = (predicate action) (define (cond-else-clause? clause) (eq? (cond-predicate clause) 'else)) (define (cond-predicate clause) (car clause)) (define (cond-actions clause) (cdr clause)) (define (cond->if exp) (expand-clauses (cond-clauses exp))) ;; (cond (p1 action1) ;; (p2 action2-1 action2-2) ;; (else last-action)) ;; (if p1 ;; action1 ;; (if p2 ;; (begin action2-1 action2-2) ;; last-action))) ;;(when p ac) = (if p ac false) (define (expand-clauses clauses) (if (null? clauses) #f (let ((first (car clauses)) (rest (cdr clauses))) (if (cond-else-clause? first) (if (null? rest) (sequence->exp (cond-actions first)) (error "ELSE clause isn't last -- COND->IF" clauses)) (make-if (cond-predicate first) (sequence->exp (cond-actions first)) (expand-clauses rest)))))) ;; 4.2 ;;a. ;; application? procedure's function is just checking whether pair?. so, some of the case it return true. ;; when with the expression (define x 3), it trys to apply "define" procedure. ;;b. ;; (define (application? exp) (tagged-list? exp 'call)) ;; (define (operator exp) (cadr exp)) ;; (define (operand exp) (caddr exp))
