79 lines
2.2 KiB
Scheme
79 lines
2.2 KiB
Scheme
(load "util.scm")
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(load "misc/evaluator.scm")
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(display "\nex-4.1 - list-of-values\n")
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(define (list-of-values-left-to-right exps env)
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(if (no-operands? exps)
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'()
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(let ((first (eval (first-operand exps) env)))
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(let ((rest ((list-of-values (rest-operands exps) env))))
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(cons first rest)))))
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(define (list-of-values-right-to-left exps env)
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(if (no-operands? exps)
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'()
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(let ((rest ((list-of-values (rest-operands exps) env))))
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(let ((first (eval (first-operand exps) env)))
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(cons first rest)))))
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(display "[done]\n")
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(display "\nex-4.2 - explicite-call\n")
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; Louis's plan does not work because the implementation would treat assignments
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; and definitions as applications. That means define and set! would no longer be
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; special forms.
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(define (application?-call exp) (tagged-list exp 'call))
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(define (operator-call exp) (cadr exp))
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(define (operands-call exp) (cddr exp))
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(display "[done]\n")
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(display "\nex-4.3 - data-directed-eval\n")
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(define *eval-table* (make-hash-table))
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(define (put op proc)
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(hash-table/put! *eval-table* (list op) proc))
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(define (get op)
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(hash-table/get *eval-table* (list op) #f))
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(define (install-eval-package)
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(put 'quote (lambda (exp env) (text-of-quotation exp)))
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(put 'set! eval-assignment)
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(put 'define eval-definition)
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(put 'if eval-if)
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(put 'lambda
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(lambda (exp env)
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(make-procedure (lambda-parameters exp)
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(lambda-body exp)
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env)))
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(put 'begin (lambda (exp env) (eval-sequence (begin-actions exp) env)))
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(put 'cond (lambda (exp env) (eval (cond->if exp) env)))
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(put 'and (lambda (exp env) 'TODO))
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(put 'or (lambda (exp env) 'TODO))
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(display "[install-eval-package]\n")
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'done)
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(install-eval-package)
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(define (eval exp env)
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(cond
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((self-evaluating? exp) exp)
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((variable? exp) (lookup-variable-value exp env))
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((and (not (null? exp))
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(get (car exp)))
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((get (car exp)) exp env))
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((application? exp)
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(apply (eval (operator exp) env)
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(list-of-values (operands exp) env)))
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(else (error "Unknown expression type -- EVAL" exp))))
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(display "[done]\n")
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(display "\nex-4.5 - and/or\n")
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(display "\nex-4.6\n")
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