49 lines
1.3 KiB
Plaintext
49 lines
1.3 KiB
Plaintext
; Stuff common to scheme.lsp and tail.lsp.
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; Environment operations
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(define extend-env
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(lambda (vars vals env)
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(cons (cons vars vals) env)))
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(define lookup-variable
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(lambda (var env)
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(if (null? env)
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(eval var) ; to give access to Lisp primitives and constants
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(lookup-in-frame var (caar env) (cdar env) (cdr env)))))
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(define lookup-in-frame
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(lambda (var vars vals enclosing-env)
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(if (null? vars)
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(lookup-variable var enclosing-env)
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(if (eq? (car vars) var)
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(car vals)
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(lookup-in-frame var (cdr vars) (cdr vals) enclosing-env)))))
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(define define-variable-value
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(lambda (var value env)
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(let ((frame (car env)))
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(set-car! frame (cons var (car frame)))
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(set-cdr! frame (cons value (cdr frame))))))
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; Syntax
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(define cadar (lambda (lst) (cadr (car lst))))
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(define cdddr (lambda (lst) (cddr (cdr lst))))
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(define caddar (lambda (lst) (cadr (cdr (car lst)))))
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(define test-exp cadr)
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(define then-exp caddr)
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(define else-exp (lambda (exp) (if (cdddr exp) (cadddr exp) nil)))
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(define make-closure cons)
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(define closure-formals cadar)
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(define closure-body caddar)
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(define closure-env cdr)
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(define primitive?
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(lambda (object)
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(and (pair? object)
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(eq? (car object) '%prim))))
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