350 lines
12 KiB
Scheme
350 lines
12 KiB
Scheme
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;;; Work in progress
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;;; Oscar Waddell. "Extending the Scope of Syntactic Abstraction". PhD.
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;;; Thesis. Indiana University Computer Science Department. August 1999.
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;;; Available online:
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;;; http://www.cs.indiana.edu/~owaddell/papers/thesis.ps.gz
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(module (source-optimize optimize-level)
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(define who 'source-optimize)
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;;; this define-structure definition for compatibility with the
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;;; notation used in Oscar's thesis.
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(define-syntax define-structure
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(lambda (stx)
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(define (fmt ctxt)
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(lambda (str . args)
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(datum->syntax ctxt
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(string->symbol
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(apply format str (map syntax->datum args))))))
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(syntax-case stx ()
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[(_ (name fields ...))
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#'(define-struct name (fields ...))]
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[(_ (name fields ...) ([others defaults] ...))
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(with-syntax ([(pred maker (getters ...) (setters ...))
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(let ([fmt (fmt #'name)])
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(list (fmt "~s?" #'name)
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(fmt "make-~s" #'name)
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(map (lambda (x) (fmt "~s-~s" #'name x))
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#'(fields ... others ...))
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(map (lambda (x) (fmt "set-~s-~s!" #'name x))
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#'(fields ... others ...))))])
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#'(module (name pred getters ... setters ... maker)
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(module P (name pred getters ... setters ... maker)
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(define-struct name (fields ... others ...)))
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(module (maker)
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(define (maker fields ...)
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(import P)
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(maker fields ... defaults ...)))
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(module (name pred getters ... setters ...)
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(import P))))])))
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;;;
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(define-structure (prelex name operand)
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([source-referenced? #f]
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[source-assigned? #f]
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[residual-referenced? #f]
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[residual-assigned? #f]))
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;;;
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(define-structure (app rand* ctxt)
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([inlined #f]))
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;;;
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(define-structure (operand expr env)
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([value #f]
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[residualize-for-effect #f]))
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;;;
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(module (init-var! var-info)
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(define (init-var! x)
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(set-var-index! x (make-prelex #f #f)))
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(define (var-info x)
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(let ([v (var-index x)])
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(if (prelex? v)
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v
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(error 'var-info "not initialized" x)))))
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(module (with-extended-env)
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(define (extend e args rands)
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(error 'extend "not yet"))
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(define-syntax with-extended-env
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(syntax-rules ()
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[(_ ((e2 args2) (e1 args1 rands)) b b* ...)
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(let-values ([(e2 args2) (extend e1 args1 rands)])
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b b* ...)])))
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;;; purpose of prepare:
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;;; 1. attach an info struct to every bound variable
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;;; 2. set the plref and plset flags to indicate whether
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;;; there is a reference/assignment to the variable.
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;;; 3. verify well-formness of the input.
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(define (prepare x)
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(define (L x)
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(for-each
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(lambda (x)
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(struct-case x
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[(clambda-case info body)
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(for-each init-var! (case-info-args info))
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(E body)]))
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(clambda-cases x)))
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(define (E x)
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(struct-case x
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[(constant) (void)]
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[(var) (set-prelex-source-referenced?! (var-info x) #t)]
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[(primref) (void)]
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[(clambda) (L x)]
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[(seq e0 e1) (E e0) (E e1)]
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[(conditional e0 e1 e2)
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(E e0) (E e1) (E e2)]
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[(assign x val)
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(set-prelex-source-assigned?! (var-info x) #t)
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(E val)]
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[(bind lhs* rhs* body)
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(for-each E rhs*)
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(for-each init-var! lhs*)
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(E body)]
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[(fix lhs* rhs* body)
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(for-each init-var! lhs*)
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(for-each L rhs*)
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(E body)
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(for-each ;;; sanity check
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(lambda (x)
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(assert (not (prelex-source-assigned? (var-info x)))))
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lhs*)]
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[(funcall rator rand*)
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(for-each E rand*)
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(E rator)]
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[(forcall name rand*)
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(for-each E rand*)]
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[else (error who "invalid expr in prepare" x)]))
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(E x))
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;;; business
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(define-syntax ctxt-case
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(lambda (stx)
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(define (test x)
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(case (syntax->datum x)
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[(p) #'(eq? t 'p)]
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[(v) #'(eq? t 'v)]
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[(e) #'(eq? t 'e)]
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[(app) #'(app? t)]
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[else (syntax-violation stx "invalid ctxt" x)]))
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(define (extract cls*)
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(syntax-case cls* (else)
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[([else e e* ...]) #'(begin e e* ...)]
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[([(t* ...) e e* ...] rest ...)
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(with-syntax ([(t* ...) (map test #'(t* ...))]
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[body (extract #'(rest ...))])
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#'(if (or t* ...)
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(begin e e* ...)
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body))]))
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(syntax-case stx ()
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[(_ expr cls* ...)
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(with-syntax ([body (extract #'(cls* ...))])
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#'(let ([t expr])
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body))])))
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(define (mkseq e0 e1)
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;;; returns a (seq e0 e1) with a seq-less e1 if both
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;;; e0 and e1 are constructed properly.
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(if (simple? e0)
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e1
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(let ([e0 (struct-case e0
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[(seq e0a e0b) (if (simple? e0b) e0a e0)]
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[else e0])])
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(struct-case e1
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[(seq e1a e1b) (make-seq (make-seq e0 e1a) e1b)]
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[else (make-seq e0 e1)]))))
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;;; simple?: check quickly whether something is effect-free
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(define (simple? x)
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(struct-case x
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[(constant) #t]
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[(var) #t]
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[(primref) #t]
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[(clambda) #t]
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[else #f]))
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;;; result returns the "last" value of an expression
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(define (result-expr x)
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(struct-case x
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[(seq e0 e1) e1]
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[else x]))
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;;;
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(define (records-equal? x y ctxt)
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(struct-case x
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[(constant kx)
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(struct-case y
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[(constant ky)
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(ctxt-case ctxt
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[(e) #t]
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[(p) (if kx ky (not ky))]
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[else (eq? kx ky)])]
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[else #f])]
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[else #f]))
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;;;
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(module (E-call value-visit-operand!)
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(define (residualize-operand x)
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(or (operand-value x)
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(E (operand-expr x) (operand-env x) 'e)))
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(define (residualize-operands e rand*)
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(cond
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[(null? rand*) e]
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[(not (operand-residualize-for-effect (car rand*)))
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(residualize-operands e (cdr rand*))]
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[else
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(mkseq
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(residualize-operand (car rand*))
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(residualize-operands e (cdr rand*)))]))
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(define (value-visit-operand! rand)
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(or (operand-value rand)
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(let ([e (E (operand-expr rand) (operand-env rand) 'v)])
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(set-operand-value! rand e)
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e)))
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(define (E-call rator rand* env ctxt)
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(let ([ctxt (make-app rand* ctxt)])
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(let ([rator (E rator env ctxt)])
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(if (app-inlined ctxt)
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(residualize-operands rator rand*)
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(make-funcall rator
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(map value-visit-operand! rand*)))))))
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;;;
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(define (E-var x env ctxt)
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(ctxt-case ctxt
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[(e) (make-constant (void))]
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[else
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(let ([x (lookup x env)])
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(let ([opnd (prelex-operand x)])
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(if opnd
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(begin
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(value-visit-operand! opnd)
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(if (prelex-source-assigned? x)
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(residualize-ref x)
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(copy x opnd ctxt)))
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(residualize-ref x))))]))
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;;;
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(define (copy x opnd ctxt)
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(let ([rhs (result-expr (operand-value opnd))])
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(struct-case rhs
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[(constant) rhs]
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[(var)
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(if (prelex-source-assigned? rhs)
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(residualize-ref x)
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(let ([opnd (prelex-operand rhs)])
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(if (and opnd (operand-value opnd))
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(copy2 rhs opnd ctxt)
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(residualize-ref rhs))))]
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[else (copy2 x opnd ctxt)])))
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(define (copy2 x opnd ctxt)
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(let ([rhs (result-expr (operand-value opnd))])
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(struct-case rhs
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[(clambda)
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(ctxt-case ctxt
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[(v) (residualize-ref x)]
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[(p) (make-constant #t)]
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[(e) (make-constant (void))]
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[(app) (inline rhs ctxt empty-env)]
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[else (error 'copy2 "cannot happen")])]
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[(primref p)
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(ctxt-case ctxt
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[(v) rhs]
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[(p) (make-constant #t)]
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[(e) (make-constant (void))]
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[(app) (fold-prim p ctxt)]
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[else (error 'copy2 "cannot happen")])]
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[else (residualize-ref x)])))
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;;;
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(define (inline proc ctxt env)
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(struct-case proc
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[(clambda g cases cp free name)
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(let ([rand* (app-rand* ctxt)])
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(struct-case (get-case cases rand*)
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[(clambda-case info body)
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(struct-case info
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[(case-info label args proper)
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(with-extended-env ((env args) (env args rand*))
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(let ([body (E body (app-ctxt ctxt) env)])
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(let ([result (make-let-binding args rand* body)])
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(set-app-inlined! ctxt #t)
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result)))])]
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[else proc]))]))
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;;;
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(define (make-let-binding args rand* body)
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(error 'make-let-binding "not yet"))
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(define (get-case . args)
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(error 'get-case "not yet"))
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;;;
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(define (fold-prim p ctxt)
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(make-primref p))
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;;;
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(define (residualize-ref x)
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(set-prelex-residual-referenced?! (var-info x) #t)
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x)
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;;;
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(define (E x env ctxt)
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(struct-case x
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[(constant) x]
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[(var) (E-var x env ctxt)]
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[(seq e0 e1)
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(mkseq (E e0 env 'e) (E e1 env ctxt))]
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[(conditional e0 e1 e2)
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(let ([e0 (E e0 env 'p)])
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(struct-case (result-expr e0)
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[(constant k)
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(mkseq e0 (E (if k e1 e2) env ctxt))]
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[else
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(let ([ctxt (ctxt-case ctxt [(app) 'v] [else ctxt])])
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(let ([e1 (E e1 env ctxt)]
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[e2 (E e2 env ctxt)])
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(if (records-equal? e1 e2 ctxt)
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(mkseq e0 e1)
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(make-conditional e0 e1 e2))))]))]
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[(assign x v)
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(mkseq
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(let ([xi (var-info x)])
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(cond
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[(not (prelex-source-referenced? xi))
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;;; dead on arrival
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(E v env 'e)]
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[else
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(set-prelex-residual-assigned?! xi #t)
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(make-assign x (E v env 'v))]))
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(make-constant (void)))]
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[(funcall rator rand*)
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(E-call rator (map (make-operand env) rand*) env ctxt)]
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[(primref name)
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(ctxt-case ctxt
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[(app) (fold-prim env ctxt)]
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[(v) x]
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[else (make-constant (void))])]
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[(clambda g cases cp free name)
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(ctxt-case ctxt
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[(app) (inline x env ctxt)]
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[(p e) (make-constant (void))]
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[else
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(make-clambda g
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(map
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(lambda (x)
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(struct-case x
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[(clambda-case info body)
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(struct-case info
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[(case-info label args proper)
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(with-extended-env ((env args) (env args #f))
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(make-clambda-case
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(make-case-info label args proper)
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(E body env 'v)))])]))
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cases)
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cp free name)])]
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[else (error who "invalid expression" x)]))
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(define empty-env '())
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(define (lookup . args)
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(error 'lookup "not yet"))
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(define optimize-level
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(make-parameter #f))
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(define (source-optimize expr)
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(cond
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[(equal? (optimize-level) 17)
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(prepare expr)
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(pretty-print (unparse expr))
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(let ([expr (E expr empty-env 'v)])
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(pretty-print (unparse expr))
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expr)]
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[else expr])))
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