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SICP 問題 4.03

scheme SICP
;; evalをデータ主導スタイルに書き換える.
;; 本文で定義されたeval
(define (eval exp env)
  (cond ((self-evaluating? exp) exp)
        ((variable? exp) (lookup-valiable-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))))

;; opを持つexpと持たないexpで分ける.
(define (eval exp env)
  (cond ((self-evaluating? exp) exp)
        ((variable? exp) (lookup-valiable-value exp env))
        (let ((op (get 'eval (operator exp)))) ;;opが見付からなければfalseが束縛
          (cond (op
                 (op (operands exp) env))
                ((application? exp)
                 (apply (eval (operator exp) env)
                        (list-of-values (operands exp) env)))
                (else
                 (error "Unknown expression type: EVAL" exp))))))


(define (make-table)
  (let ((local-table (list '*table*)))
    (define (lookup key-1 key-2)
      (let ((subtable (assoc key-1 (cdr local-table))))
        (if subtable
            (let ((record (assoc key-2 (cdr subtable))))
              (if record
                  (cdr record)
                  false))
            false)))
    (define (insert! key-1 key-2 value)
      (let ((subtable (assoc key-1 (cdr local-table))))
        (if subtable
            (let ((record (assoc key-2 (cdr subtable))))
              (if record
                  (set-cdr! record value)
                  (set-cdr! subtable
                            (cons (cons key-2 value)
                                  (cdr subtable)))))
            (set-cdr! local-table
                      (cons (list key-1
                                  (cons key-2 value))
                            (cdr local-table)))))
      'ok)
    (define (dispatch m)
      (cond ((eq? m 'lookup-proc) lookup)
            ((eq? m 'insert-proc!) insert!)
            (else (error "Unknown operation -- TABLE" m))))
    dispatch))

(define operation-table (make-table))
(define get (operation-table 'lookup-proc))
(define put (operation-table 'insert-proc!))

(define (install-eval-package)
  ;; クオート式
  (define (text-of-quotation exp) (cadr exp))
  ;; 代入
  (define (eval-assignment exp env)
    (set-variable-value! (assignment-variable exp)
                         (eval (assignment-value exp) env)
                         env)
    'ok)
  ;; 定義
  (define (eval-definition exp env)
    (define-variable! (definition-variable exp)
      (eval (definition-value exp) env)
      env)
    'ok)
  ;; 条件式
  (define (eval-if exp env)
    (if (true? (eval (if-predicate exp) env))
        (eval (if-consequent exp) env)
        (eval (if-alternative exp) env)))
  ;; lambda
  (define (lambda-parameters exp) (cadr exp))
  (define (lambda-body exp) (cddr exp))
  ;; 列
  (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 (begin-actions exp) (cdr exp))
  (define (cond->if exp) (expand-clauses (cond-clauses exp)))
  (define (expand-clauses clauses)
    (if (null? clauses)
        'false ;; else 説は無い
        (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))))))
  (put 'eval 'quote text-of-quotation)
  (put 'eval 'set! eval-assignment)
  (put 'eval 'define eval-definition)v
  (put 'eval 'if eval-if)
  (put 'eval 'lambda (lambda (exp env) (make-procedure (lambda-parameters exp)
                                                       (lambda-body exp)
                                                       env)))
  (put 'eval 'begin (lambda (exp env) (eval-sequence (begin-actions exp) env)))
  (put 'eval 'cond (lambda (exp env) (eval (cond->if exp) env)))
'done)