381 lines
12 KiB
Scheme
381 lines
12 KiB
Scheme
;;;;COMPILER FROM SECTION 5.5 OF
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;;;; STRUCTURE AND INTERPRETATION OF COMPUTER PROGRAMS
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;;;;Matches code in ch5.scm
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;;;;This file can be loaded into Scheme as a whole.
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;;;;**NOTE**This file loads the metacircular evaluator's syntax procedures
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;;;; from section 4.1.2
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;;;; You may need to change the (load ...) expression to work in your
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;;;; version of Scheme.
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;;;;Then you can compile Scheme programs as shown in section 5.5.5
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;;**implementation-dependent loading of syntax procedures
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(load "ch5-syntax.scm") ;section 4.1.2 syntax procedures
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;;;SECTION 5.5.1
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(define (compile exp target linkage)
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(cond ((self-evaluating? exp)
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(compile-self-evaluating exp target linkage))
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((quoted? exp) (compile-quoted exp target linkage))
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((variable? exp)
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(compile-variable exp target linkage))
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((assignment? exp)
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(compile-assignment exp target linkage))
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((definition? exp)
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(compile-definition exp target linkage))
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((if? exp) (compile-if exp target linkage))
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((lambda? exp) (compile-lambda exp target linkage))
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((begin? exp)
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(compile-sequence (begin-actions exp)
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target
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linkage))
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((cond? exp) (compile (cond->if exp) target linkage))
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((application? exp)
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(compile-application exp target linkage))
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(else
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(error "Unknown expression type -- COMPILE" exp))))
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(define (make-instruction-sequence needs modifies statements)
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(list needs modifies statements))
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(define (empty-instruction-sequence)
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(make-instruction-sequence '() '() '()))
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;;;SECTION 5.5.2
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;;;linkage code
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(define (compile-linkage linkage)
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(cond ((eq? linkage 'return)
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(make-instruction-sequence '(continue) '()
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'((goto (reg continue)))))
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((eq? linkage 'next)
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(empty-instruction-sequence))
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(else
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(make-instruction-sequence '() '()
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`((goto (label ,linkage)))))))
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(define (end-with-linkage linkage instruction-sequence)
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(preserving '(continue)
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instruction-sequence
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(compile-linkage linkage)))
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;;;simple expressions
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(define (compile-self-evaluating exp target linkage)
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(end-with-linkage linkage
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(make-instruction-sequence '() (list target)
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`((assign ,target (const ,exp))))))
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(define (compile-quoted exp target linkage)
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(end-with-linkage linkage
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(make-instruction-sequence '() (list target)
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`((assign ,target (const ,(text-of-quotation exp)))))))
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(define (compile-variable exp target linkage)
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(end-with-linkage linkage
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(make-instruction-sequence '(env) (list target)
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`((assign ,target
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(op lookup-variable-value)
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(const ,exp)
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(reg env))))))
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(define (compile-assignment exp target linkage)
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(let ((var (assignment-variable exp))
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(get-value-code
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(compile (assignment-value exp) 'val 'next)))
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(end-with-linkage linkage
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(preserving '(env)
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get-value-code
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(make-instruction-sequence '(env val) (list target)
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`((perform (op set-variable-value!)
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(const ,var)
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(reg val)
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(reg env))
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(assign ,target (const ok))))))))
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(define (compile-definition exp target linkage)
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(let ((var (definition-variable exp))
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(get-value-code
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(compile (definition-value exp) 'val 'next)))
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(end-with-linkage linkage
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(preserving '(env)
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get-value-code
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(make-instruction-sequence '(env val) (list target)
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`((perform (op define-variable!)
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(const ,var)
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(reg val)
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(reg env))
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(assign ,target (const ok))))))))
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;;;conditional expressions
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;;;labels (from footnote)
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(define label-counter 0)
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(define (new-label-number)
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(set! label-counter (+ 1 label-counter))
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label-counter)
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(define (make-label name)
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(string->symbol
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(string-append (symbol->string name)
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(number->string (new-label-number)))))
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;; end of footnote
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(define (compile-if exp target linkage)
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(let ((t-branch (make-label 'true-branch))
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(f-branch (make-label 'false-branch))
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(after-if (make-label 'after-if)))
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(let ((consequent-linkage
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(if (eq? linkage 'next) after-if linkage)))
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(let ((p-code (compile (if-predicate exp) 'val 'next))
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(c-code
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(compile
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(if-consequent exp) target consequent-linkage))
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(a-code
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(compile (if-alternative exp) target linkage)))
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(preserving '(env continue)
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p-code
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(append-instruction-sequences
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(make-instruction-sequence '(val) '()
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`((test (op false?) (reg val))
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(branch (label ,f-branch))))
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(parallel-instruction-sequences
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(append-instruction-sequences t-branch c-code)
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(append-instruction-sequences f-branch a-code))
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after-if))))))
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;;; sequences
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(define (compile-sequence seq target linkage)
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(if (last-exp? seq)
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(compile (first-exp seq) target linkage)
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(preserving '(env continue)
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(compile (first-exp seq) target 'next)
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(compile-sequence (rest-exps seq) target linkage))))
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;;;lambda expressions
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(define (compile-lambda exp target linkage)
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(let ((proc-entry (make-label 'entry))
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(after-lambda (make-label 'after-lambda)))
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(let ((lambda-linkage
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(if (eq? linkage 'next) after-lambda linkage)))
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(append-instruction-sequences
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(tack-on-instruction-sequence
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(end-with-linkage lambda-linkage
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(make-instruction-sequence '(env) (list target)
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`((assign ,target
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(op make-compiled-procedure)
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(label ,proc-entry)
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(reg env)))))
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(compile-lambda-body exp proc-entry))
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after-lambda))))
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(define (compile-lambda-body exp proc-entry)
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(let ((formals (lambda-parameters exp)))
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(append-instruction-sequences
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(make-instruction-sequence '(env proc argl) '(env)
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`(,proc-entry
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(assign env (op compiled-procedure-env) (reg proc))
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(assign env
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(op extend-environment)
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(const ,formals)
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(reg argl)
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(reg env))))
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(compile-sequence (lambda-body exp) 'val 'return))))
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;;;SECTION 5.5.3
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;;;combinations
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(define (compile-application exp target linkage)
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(let ((proc-code (compile (operator exp) 'proc 'next))
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(operand-codes
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(map (lambda (operand) (compile operand 'val 'next))
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(operands exp))))
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(preserving '(env continue)
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proc-code
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(preserving '(proc continue)
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(construct-arglist operand-codes)
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(compile-procedure-call target linkage)))))
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(define (construct-arglist operand-codes)
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(let ((operand-codes (reverse operand-codes)))
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(if (null? operand-codes)
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(make-instruction-sequence '() '(argl)
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'((assign argl (const ()))))
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(let ((code-to-get-last-arg
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(append-instruction-sequences
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(car operand-codes)
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(make-instruction-sequence '(val) '(argl)
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'((assign argl (op list) (reg val)))))))
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(if (null? (cdr operand-codes))
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code-to-get-last-arg
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(preserving '(env)
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code-to-get-last-arg
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(code-to-get-rest-args
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(cdr operand-codes))))))))
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(define (code-to-get-rest-args operand-codes)
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(let ((code-for-next-arg
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(preserving '(argl)
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(car operand-codes)
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(make-instruction-sequence '(val argl) '(argl)
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'((assign argl
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(op cons) (reg val) (reg argl)))))))
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(if (null? (cdr operand-codes))
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code-for-next-arg
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(preserving '(env)
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code-for-next-arg
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(code-to-get-rest-args (cdr operand-codes))))))
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;;;applying procedures
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(define (compile-procedure-call target linkage)
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(let ((primitive-branch (make-label 'primitive-branch))
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(compiled-branch (make-label 'compiled-branch))
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(after-call (make-label 'after-call)))
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(let ((compiled-linkage
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(if (eq? linkage 'next) after-call linkage)))
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(append-instruction-sequences
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(make-instruction-sequence '(proc) '()
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`((test (op primitive-procedure?) (reg proc))
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(branch (label ,primitive-branch))))
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(parallel-instruction-sequences
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(append-instruction-sequences
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compiled-branch
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(compile-proc-appl target compiled-linkage))
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(append-instruction-sequences
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primitive-branch
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(end-with-linkage linkage
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(make-instruction-sequence '(proc argl)
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(list target)
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`((assign ,target
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(op apply-primitive-procedure)
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(reg proc)
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(reg argl)))))))
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after-call))))
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;;;applying compiled procedures
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(define (compile-proc-appl target linkage)
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(cond ((and (eq? target 'val) (not (eq? linkage 'return)))
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(make-instruction-sequence '(proc) all-regs
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`((assign continue (label ,linkage))
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(assign val (op compiled-procedure-entry)
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(reg proc))
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(goto (reg val)))))
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((and (not (eq? target 'val))
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(not (eq? linkage 'return)))
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(let ((proc-return (make-label 'proc-return)))
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(make-instruction-sequence '(proc) all-regs
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`((assign continue (label ,proc-return))
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(assign val (op compiled-procedure-entry)
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(reg proc))
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(goto (reg val))
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,proc-return
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(assign ,target (reg val))
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(goto (label ,linkage))))))
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((and (eq? target 'val) (eq? linkage 'return))
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(make-instruction-sequence '(proc continue) all-regs
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'((assign val (op compiled-procedure-entry)
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(reg proc))
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(goto (reg val)))))
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((and (not (eq? target 'val)) (eq? linkage 'return))
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(error "return linkage, target not val -- COMPILE"
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target))))
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;; footnote
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(define all-regs '(env proc val argl continue))
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;;;SECTION 5.5.4
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(define (registers-needed s)
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(if (symbol? s) '() (car s)))
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(define (registers-modified s)
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(if (symbol? s) '() (cadr s)))
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(define (statements s)
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(if (symbol? s) (list s) (caddr s)))
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(define (needs-register? seq reg)
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(memq reg (registers-needed seq)))
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(define (modifies-register? seq reg)
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(memq reg (registers-modified seq)))
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(define (append-instruction-sequences . seqs)
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(define (append-2-sequences seq1 seq2)
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(make-instruction-sequence
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(list-union (registers-needed seq1)
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(list-difference (registers-needed seq2)
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(registers-modified seq1)))
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(list-union (registers-modified seq1)
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(registers-modified seq2))
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(append (statements seq1) (statements seq2))))
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(define (append-seq-list seqs)
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(if (null? seqs)
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(empty-instruction-sequence)
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(append-2-sequences (car seqs)
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(append-seq-list (cdr seqs)))))
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(append-seq-list seqs))
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(define (list-union s1 s2)
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(cond ((null? s1) s2)
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((memq (car s1) s2) (list-union (cdr s1) s2))
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(else (cons (car s1) (list-union (cdr s1) s2)))))
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(define (list-difference s1 s2)
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(cond ((null? s1) '())
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((memq (car s1) s2) (list-difference (cdr s1) s2))
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(else (cons (car s1)
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(list-difference (cdr s1) s2)))))
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(define (preserving regs seq1 seq2)
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(if (null? regs)
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(append-instruction-sequences seq1 seq2)
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(let ((first-reg (car regs)))
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(if (and (needs-register? seq2 first-reg)
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(modifies-register? seq1 first-reg))
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(preserving (cdr regs)
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(make-instruction-sequence
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(list-union (list first-reg)
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(registers-needed seq1))
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(list-difference (registers-modified seq1)
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(list first-reg))
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(append `((save ,first-reg))
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(statements seq1)
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`((restore ,first-reg))))
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seq2)
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(preserving (cdr regs) seq1 seq2)))))
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(define (tack-on-instruction-sequence seq body-seq)
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(make-instruction-sequence
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(registers-needed seq)
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(registers-modified seq)
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(append (statements seq) (statements body-seq))))
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(define (parallel-instruction-sequences seq1 seq2)
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(make-instruction-sequence
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(list-union (registers-needed seq1)
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(registers-needed seq2))
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(list-union (registers-modified seq1)
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(registers-modified seq2))
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(append (statements seq1) (statements seq2))))
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'(COMPILER LOADED)
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