56 lines
1.4 KiB
Plaintext
56 lines
1.4 KiB
Plaintext
; This ain't a Scheme interpreter, despite the filename.
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; Uses: startup scmhelp.lsp
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(define read-eval-print-loop
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(lambda ()
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(let ((exp '*))
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(while (begin
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(write '>)
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(not (eq? the-eof-object (set! exp (read)))))
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(print (eval-exp (macroexpand exp) init-env))))))
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(define eval-exp
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(lambda (exp env)
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((evaluator exp) exp env)))
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(define evaluator
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(lambda (exp)
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(if (atom? exp)
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(if (symbol? exp) lookup-variable self-evaluating)
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(or (get (car exp) 'evaluator)
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(lambda (exp env)
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(apply-proc (eval-exp (car exp) env)
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(map (lambda (rand) (eval-exp rand env)) (cdr exp))))))))
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(define self-evaluating
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(lambda (exp env) exp))
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(put 'quote 'evaluator
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(lambda (exp env) (cadr exp)))
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(put 'lambda 'evaluator make-closure)
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(put 'if 'evaluator
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(lambda (exp env)
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(if (eval-exp (test-exp exp) env)
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(eval-exp (then-exp exp) env)
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(eval-exp (else-exp exp) env))))
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(put 'define 'evaluator
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(lambda (exp env)
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(define-variable-value (cadr exp) (eval-exp (caddr exp) env) env)
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(cadr exp)))
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(define apply-proc
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(lambda (proc args)
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(if (primitive? proc)
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(apply proc args)
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(eval-exp (closure-body proc)
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(extend-env (closure-formals proc) args (closure-env proc))))))
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; Here we go
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(define init-env (extend-env '() '() '()))
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(read-eval-print-loop)
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