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4.2.scm
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4.2.scm
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(load "./util.scm")
(define extend
(lambda (e r)
(cons r e)))
(define compile
(lambda (x e next)
(cond ((symbol? x)
(compile-lookup x e
(lambda (n m)
(list 'refer n m next))))
((pair? x)
(record-case x
(quote (obj)
(list 'constant obj next))
(lambda (vars body)
(list 'close
(compile body
(extend e vars)
(list 'return))
next))
(if (test then else)
(let ((thenc (compile then e next))
(elsec (compile else e next)))
(compile test e (list 'test thenc elsec))))
(else
(recur loop ((args (cdr x))
(c (compile (car x) e '(apply))))
(if (null? args)
(list 'frame next c)
(loop (cdr args)
(compile (car args)
e
(list 'argument c))))))))
(else
(list 'constant x next)))))
(define compile-lookup
(lambda (var e return)
(recur nxtrib ((e e) (rib 0))
(if (null? e)
(error "undefined" var)
(recur nxtelt ((vars (car e)) (elt 0))
(cond
((null? vars) (nxtrib (cdr e) (+ rib 1)))
((eq? (car vars) var) (return rib elt))
(else (nxtelt (cdr vars) (+ elt 1)))))))))
;;;; runtime
(define stack (make-vector 1000))
(define push
(lambda (x s)
(vector-set! stack s x)
(+ s 1)))
(define index
(lambda (s i)
(vector-ref stack (- (- s i) 1))))
(define index-set!
(lambda (s i v)
(vector-set! stack (- (- s i) 1) v)))
;;;; VM
(define VM
(lambda (a x e r s)
(record-case x
(halt () a)
(refer (n m x)
(VM (car (lookup n m e)) x e r s))
(constant (obj x)
(VM obj x e r s))
(close (body x)
(VM (closure body e) x e r s))
(test (then else)
(VM a (if a then else) e r s))
(assign (n m x)
(set-car! (lookup n m e) a)
(VM a x e r s))
(conti (x)
(VM (continuation s) x e r s))
(nuate (stack x)
(VM a x e r (restore-stack stack)))
(frame (ret x)
(VM a x e '() (push ret (push e (push r s)))))
(argument (x)
(VM a x e (cons a r) s))
(apply ()
(record a (body e)
(VM a body (extend e r) '() s)))
(return ()
(VM a (index s 0) (index s 1) (index s 2) (- s 3))))))
(define continuation
(lambda (s)
(closure
(list 'refer 0 0 (list 'nuate (save-stack s) '(return)))
'())))
(define closure
(lambda (body e)
(list body e)))
(define save-stack
(lambda (s)
(let ((v (make-vector s)))
(recur copy ((i 0))
(unless (= i s)
(vector-set! v i (vector-ref stack i))
(copy (+ i 1))))
v)))
(define restore-stack
(lambda (v)
(let ((s (vector-length v)))
(recur copy ((i 0))
(unless (= i s)
(vector-set! stack i (vector-ref v i))
(copy (+ i 1))))
s)))
(define lookup
(lambda (n m e)
(recur nxtrib ((e e) (rib n))
(if (= rib 0)
(recur nxtelt ((r (car e)) (elt m))
(if (= elt 0)
r
(nxtelt (cdr r) (- elt 1))))
(nxtrib (cdr e) (- rib 1))))))
(define evaluate
(lambda (x)
(let1 code (compile x '() '(halt))
(VM '() code '() '() 0))))