SICP/ex-4_01-xx.scm

(load "util.scm")
(load "misc/evaluator.scm")

(display "\nex-4.1 - list-of-values\n")

(define (list-of-values-left-to-right exps env)
  (if (no-operands? exps)
      '()
      (let ((first (eval (first-operand exps) env)))
        (let ((rest ((list-of-values (rest-operands exps) env))))
          (cons first rest)))))

(define (list-of-values-right-to-left exps env)
  (if (no-operands? exps)
      '()
      (let ((rest ((list-of-values (rest-operands exps) env))))
        (let ((first (eval (first-operand exps) env)))
          (cons first rest)))))

(display "[done]\n")

(display "\nex-4.2 - explicite-call\n")

; Louis's plan does not work because the implementation would treat assignments
; and definitions as applications. That means define and set! would no longer be
; special forms.

(define (application?-call exp) (tagged-list exp 'call))
(define (operator-call exp) (cadr exp))
(define (operands-call exp) (cddr exp))

(display "[done]\n")

(display "\nex-4.3 - data-directed-eval\n")

(define *eval-table* (make-hash-table))
(define (put op proc)
  (hash-table/put! *eval-table* (list op) proc))
(define (get op)
  (hash-table/get *eval-table* (list op) #f))

(define (install-eval-package)
  (put 'quote (lambda (exp env) (text-of-quotation exp)))
  (put 'set! eval-assignment)
  (put 'define eval-definition)
  (put 'if eval-if)
  (put 'lambda
       (lambda (exp env)
         (make-procedure (lambda-parameters exp)
                         (lambda-body exp)
                         env)))
  (put 'begin (lambda (exp env) (eval-sequence (begin-actions exp) env)))
  (put 'cond (lambda (exp env) (eval (cond->if exp) env)))
  (put 'and (lambda (exp env) 'TODO))
  (put 'or (lambda (exp env) 'TODO))
  (display "[install-eval-package]\n")
  'done)

(install-eval-package)

(define (eval exp env)
  (cond
    ((self-evaluating? exp) exp)
    ((variable? exp) (lookup-variable-value exp env))
    ((and (not (null? exp))
          (get (car exp)))
     ((get (car exp)) exp env))
    ((application? exp)
     (apply (eval (operator exp) env)
            (list-of-values (operands exp) env)))
    (else (error "Unknown expression type -- EVAL" exp))))

(display "[done]\n")

(display "\nex-4.5 - and/or\n")

(display "\nex-4.6\n")