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(declare (usual-integrations eval apply))
(define (default-eval expression environment)
(cond ((application? expression)
(apply (eval (operator expression) environment)
(operands expression)
environment))
(else
(error "Unknown expression type" expression))))
(define (default-apply procedure operands calling-environment)
(error "Unknown procedure type" procedure))
(define eval
(make-generic-operator 2 default-eval))
(defhandler eval
(lambda (expression environment) expression)
self-evaluating?)
(defhandler eval lookup-variable-value variable?)
(defhandler eval
(lambda (expression environment)
(text-of-quotation expression))
quoted?)
(defhandler eval
(lambda (expression environment)
(make-compound-procedure
(lambda-parameters expression)
(lambda-body expression)
environment))
lambda?)
(defhandler eval
(lambda (expression environment)
(if (eval (if-predicate expression) environment)
(eval (if-consequent expression) environment)
(eval (if-alternative expression) environment)))
if?)
(defhandler eval
(lambda (expression environment)
(eval (cond->if expression) environment))
cond?)
(defhandler eval
(lambda (expression environment)
(eval (let->combination expression) environment))
let?)
(defhandler eval
(lambda (expression environment)
(evaluate-sequence (begin-actions expression)
environment))
begin?)
(define (evaluate-sequence actions environment)
(cond ((null? actions)
(error "Empty sequence"))
((null? (rest-exps actions))
(eval (first-exp actions) environment))
(else
(eval (first-exp actions) environment)
(evaluate-sequence (rest-exps actions) environment))))
(defhandler eval
(lambda (expression environment)
(define-variable! (definition-variable expression)
(eval (definition-value expression) environment)
environment)
(definition-variable expression))
definition?)
(defhandler eval
(lambda (expression environment)
(set-variable-value! (assignment-variable expression)
(eval (assignment-value expression) environment)
environment))
assignment?)
(define apply
(make-generic-operator 3 default-apply))
(defhandler apply
(lambda (procedure operands calling-environment)
(apply-primitive-procedure procedure
(evaluate-list operands calling-environment)))
strict-primitive-procedure?)
(define (evaluate-list operands calling-environment)
(cond ((null? operands) '())
((null? (rest-operands operands))
(list (eval (first-operand operands)
calling-environment)))
(else
(cons (eval (first-operand operands)
calling-environment)
(evaluate-list (rest-operands operands)
calling-environment)))))
(defhandler apply
(lambda (procedure operands calling-environment)
(if (not (= (length (procedure-parameters procedure))
(length operands)))
(error "Wrong number of operands supplied"))
(let ((arguments
(map (lambda (parameter operand)
(evaluate-procedure-operand parameter
operand
calling-environment))
(procedure-parameters procedure)
operands)))
(eval (procedure-body procedure)
(extend-environment
(map procedure-parameter-name
(procedure-parameters procedure))
arguments
(procedure-environment procedure)))))
compound-procedure?)
(define evaluate-procedure-operand
(make-generic-operator 3
(lambda (parameter operand environment)
(eval operand environment))))
(define procedure-parameter-name
(make-generic-operator 1 (lambda (x) x)))
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