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;;;;COMPILER FROM SECTION 5.5 OF
;;;; STRUCTURE AND INTERPRETATION OF COMPUTER PROGRAMS
;;;;Matches code in ch5.scm
;;;;This file can be loaded into Scheme as a whole.
;;;;**NOTE**This file loads the metacircular evaluator's syntax procedures
;;;; from section 4.1.2
;;;; You may need to change the (load ...) expression to work in your
;;;; version of Scheme.
;;;;Then you can compile Scheme programs as shown in section 5.5.5
;;**implementation-dependent loading of syntax procedures
(load "ch5-syntax.scm") ;section 4.1.2 syntax procedures
;;;SECTION 5.5.1
(define (compile exp target linkage)
(cond ((self-evaluating? exp)
(compile-self-evaluating exp target linkage))
((quoted? exp) (compile-quoted exp target linkage))
((variable? exp)
(compile-variable exp target linkage))
((assignment? exp)
(compile-assignment exp target linkage))
((definition? exp)
(compile-definition exp target linkage))
((if? exp) (compile-if exp target linkage))
((lambda? exp) (compile-lambda exp target linkage))
((begin? exp)
(compile-sequence (begin-actions exp)
target
linkage))
((cond? exp) (compile (cond->if exp) target linkage))
((application? exp)
(compile-application exp target linkage))
(else
(error "Unknown expression type -- COMPILE" exp))))
(define (make-instruction-sequence needs modifies statements)
(list needs modifies statements))
(define (empty-instruction-sequence)
(make-instruction-sequence '() '() '()))
;;;SECTION 5.5.2
;;;linkage code
(define (compile-linkage linkage)
(cond ((eq? linkage 'return)
(make-instruction-sequence '(continue) '()
'((goto (reg continue)))))
((eq? linkage 'next)
(empty-instruction-sequence))
(else
(make-instruction-sequence '() '()
`((goto (label ,linkage)))))))
(define (end-with-linkage linkage instruction-sequence)
(preserving '(continue)
instruction-sequence
(compile-linkage linkage)))
;;;simple expressions
(define (compile-self-evaluating exp target linkage)
(end-with-linkage linkage
(make-instruction-sequence '() (list target)
`((assign ,target (const ,exp))))))
(define (compile-quoted exp target linkage)
(end-with-linkage linkage
(make-instruction-sequence '() (list target)
`((assign ,target (const ,(text-of-quotation exp)))))))
(define (compile-variable exp target linkage)
(end-with-linkage linkage
(make-instruction-sequence '(env) (list target)
`((assign ,target
(op lookup-variable-value)
(const ,exp)
(reg env))))))
(define (compile-assignment exp target linkage)
(let ((var (assignment-variable exp))
(get-value-code
(compile (assignment-value exp) 'val 'next)))
(end-with-linkage linkage
(preserving '(env)
get-value-code
(make-instruction-sequence '(env val) (list target)
`((perform (op set-variable-value!)
(const ,var)
(reg val)
(reg env))
(assign ,target (const ok))))))))
(define (compile-definition exp target linkage)
(let ((var (definition-variable exp))
(get-value-code
(compile (definition-value exp) 'val 'next)))
(end-with-linkage linkage
(preserving '(env)
get-value-code
(make-instruction-sequence '(env val) (list target)
`((perform (op define-variable!)
(const ,var)
(reg val)
(reg env))
(assign ,target (const ok))))))))
;;;conditional expressions
;;;labels (from footnote)
(define label-counter 0)
(define (new-label-number)
(set! label-counter (+ 1 label-counter))
label-counter)
(define (make-label name)
(string->symbol
(string-append (symbol->string name)
(number->string (new-label-number)))))
;; end of footnote
(define (compile-if exp target linkage)
(let ((t-branch (make-label 'true-branch))
(f-branch (make-label 'false-branch))
(after-if (make-label 'after-if)))
(let ((consequent-linkage
(if (eq? linkage 'next) after-if linkage)))
(let ((p-code (compile (if-predicate exp) 'val 'next))
(c-code
(compile
(if-consequent exp) target consequent-linkage))
(a-code
(compile (if-alternative exp) target linkage)))
(preserving '(env continue)
p-code
(append-instruction-sequences
(make-instruction-sequence '(val) '()
`((test (op false?) (reg val))
(branch (label ,f-branch))))
(parallel-instruction-sequences
(append-instruction-sequences t-branch c-code)
(append-instruction-sequences f-branch a-code))
after-if))))))
;;; sequences
(define (compile-sequence seq target linkage)
(if (last-exp? seq)
(compile (first-exp seq) target linkage)
(preserving '(env continue)
(compile (first-exp seq) target 'next)
(compile-sequence (rest-exps seq) target linkage))))
;;;lambda expressions
(define (compile-lambda exp target linkage)
(let ((proc-entry (make-label 'entry))
(after-lambda (make-label 'after-lambda)))
(let ((lambda-linkage
(if (eq? linkage 'next) after-lambda linkage)))
(append-instruction-sequences
(tack-on-instruction-sequence
(end-with-linkage lambda-linkage
(make-instruction-sequence '(env) (list target)
`((assign ,target
(op make-compiled-procedure)
(label ,proc-entry)
(reg env)))))
(compile-lambda-body exp proc-entry))
after-lambda))))
(define (compile-lambda-body exp proc-entry)
(let ((formals (lambda-parameters exp)))
(append-instruction-sequences
(make-instruction-sequence '(env proc argl) '(env)
`(,proc-entry
(assign env (op compiled-procedure-env) (reg proc))
(assign env
(op extend-environment)
(const ,formals)
(reg argl)
(reg env))))
(compile-sequence (lambda-body exp) 'val 'return))))
;;;SECTION 5.5.3
;;;combinations
(define (compile-application exp target linkage)
(let ((proc-code (compile (operator exp) 'proc 'next))
(operand-codes
(map (lambda (operand) (compile operand 'val 'next))
(operands exp))))
(preserving '(env continue)
proc-code
(preserving '(proc continue)
(construct-arglist operand-codes)
(compile-procedure-call target linkage)))))
(define (construct-arglist operand-codes)
(let ((operand-codes (reverse operand-codes)))
(if (null? operand-codes)
(make-instruction-sequence '() '(argl)
'((assign argl (const ()))))
(let ((code-to-get-last-arg
(append-instruction-sequences
(car operand-codes)
(make-instruction-sequence '(val) '(argl)
'((assign argl (op list) (reg val)))))))
(if (null? (cdr operand-codes))
code-to-get-last-arg
(preserving '(env)
code-to-get-last-arg
(code-to-get-rest-args
(cdr operand-codes))))))))
(define (code-to-get-rest-args operand-codes)
(let ((code-for-next-arg
(preserving '(argl)
(car operand-codes)
(make-instruction-sequence '(val argl) '(argl)
'((assign argl
(op cons) (reg val) (reg argl)))))))
(if (null? (cdr operand-codes))
code-for-next-arg
(preserving '(env)
code-for-next-arg
(code-to-get-rest-args (cdr operand-codes))))))
;;;applying procedures
(define (compile-procedure-call target linkage)
(let ((primitive-branch (make-label 'primitive-branch))
(compiled-branch (make-label 'compiled-branch))
(after-call (make-label 'after-call)))
(let ((compiled-linkage
(if (eq? linkage 'next) after-call linkage)))
(append-instruction-sequences
(make-instruction-sequence '(proc) '()
`((test (op primitive-procedure?) (reg proc))
(branch (label ,primitive-branch))))
(parallel-instruction-sequences
(append-instruction-sequences
compiled-branch
(compile-proc-appl target compiled-linkage))
(append-instruction-sequences
primitive-branch
(end-with-linkage linkage
(make-instruction-sequence '(proc argl)
(list target)
`((assign ,target
(op apply-primitive-procedure)
(reg proc)
(reg argl)))))))
after-call))))
;;;applying compiled procedures
(define (compile-proc-appl target linkage)
(cond ((and (eq? target 'val) (not (eq? linkage 'return)))
(make-instruction-sequence '(proc) all-regs
`((assign continue (label ,linkage))
(assign val (op compiled-procedure-entry)
(reg proc))
(goto (reg val)))))
((and (not (eq? target 'val))
(not (eq? linkage 'return)))
(let ((proc-return (make-label 'proc-return)))
(make-instruction-sequence '(proc) all-regs
`((assign continue (label ,proc-return))
(assign val (op compiled-procedure-entry)
(reg proc))
(goto (reg val))
,proc-return
(assign ,target (reg val))
(goto (label ,linkage))))))
((and (eq? target 'val) (eq? linkage 'return))
(make-instruction-sequence '(proc continue) all-regs
'((assign val (op compiled-procedure-entry)
(reg proc))
(goto (reg val)))))
((and (not (eq? target 'val)) (eq? linkage 'return))
(error "return linkage, target not val -- COMPILE"
target))))
;; footnote
(define all-regs '(env proc val argl continue))
;;;SECTION 5.5.4
(define (registers-needed s)
(if (symbol? s) '() (car s)))
(define (registers-modified s)
(if (symbol? s) '() (cadr s)))
(define (statements s)
(if (symbol? s) (list s) (caddr s)))
(define (needs-register? seq reg)
(memq reg (registers-needed seq)))
(define (modifies-register? seq reg)
(memq reg (registers-modified seq)))
(define (append-instruction-sequences . seqs)
(define (append-2-sequences seq1 seq2)
(make-instruction-sequence
(list-union (registers-needed seq1)
(list-difference (registers-needed seq2)
(registers-modified seq1)))
(list-union (registers-modified seq1)
(registers-modified seq2))
(append (statements seq1) (statements seq2))))
(define (append-seq-list seqs)
(if (null? seqs)
(empty-instruction-sequence)
(append-2-sequences (car seqs)
(append-seq-list (cdr seqs)))))
(append-seq-list seqs))
(define (list-union s1 s2)
(cond ((null? s1) s2)
((memq (car s1) s2) (list-union (cdr s1) s2))
(else (cons (car s1) (list-union (cdr s1) s2)))))
(define (list-difference s1 s2)
(cond ((null? s1) '())
((memq (car s1) s2) (list-difference (cdr s1) s2))
(else (cons (car s1)
(list-difference (cdr s1) s2)))))
(define (preserving regs seq1 seq2)
(if (null? regs)
(append-instruction-sequences seq1 seq2)
(let ((first-reg (car regs)))
(if (and (needs-register? seq2 first-reg)
(modifies-register? seq1 first-reg))
(preserving (cdr regs)
(make-instruction-sequence
(list-union (list first-reg)
(registers-needed seq1))
(list-difference (registers-modified seq1)
(list first-reg))
(append `((save ,first-reg))
(statements seq1)
`((restore ,first-reg))))
seq2)
(preserving (cdr regs) seq1 seq2)))))
(define (tack-on-instruction-sequence seq body-seq)
(make-instruction-sequence
(registers-needed seq)
(registers-modified seq)
(append (statements seq) (statements body-seq))))
(define (parallel-instruction-sequences seq1 seq2)
(make-instruction-sequence
(list-union (registers-needed seq1)
(registers-needed seq2))
(list-union (registers-modified seq1)
(registers-modified seq2))
(append (statements seq1) (statements seq2))))
'(COMPILER LOADED)
;;;;SCHEME SYNTAX FROM SECTION 4.1.2 OF STRUCTURE AND INTERPRETATION OF
;;; COMPUTER PROGRAMS, TO SUPPORT CHAPTER 5
;;;;Loaded by compiler.scm (for use by compiler), and by eceval-support.scm
;;;; (for simulation of eceval machine operations)
(define (self-evaluating? exp)
(cond ((number? exp) true)
((string? exp) true)
(else false)))
(define (quoted? exp)
(tagged-list? exp 'quote))
(define (text-of-quotation exp) (cadr exp))
(define (tagged-list? exp tag)
(if (pair? exp)
(eq? (car exp) tag)
false))
(define (variable? exp) (symbol? exp))
(define (assignment? exp)
(tagged-list? exp 'set!))
(define (assignment-variable exp) (cadr exp))
(define (assignment-value exp) (caddr exp))
(define (definition? exp)
(tagged-list? exp 'define))
(define (definition-variable exp)
(if (symbol? (cadr exp))
(cadr exp)
(caadr exp)))
(define (definition-value exp)
(if (symbol? (cadr exp))
(caddr exp)
(make-lambda (cdadr exp)
(cddr exp))))
(define (lambda? exp) (tagged-list? exp 'lambda))
(define (lambda-parameters exp) (cadr exp))
(define (lambda-body exp) (cddr exp))
(define (make-lambda parameters body)
(cons 'lambda (cons parameters body)))
(define (if? exp) (tagged-list? exp 'if))
(define (if-predicate exp) (cadr exp))
(define (if-consequent exp) (caddr exp))
(define (if-alternative exp)
(if (not (null? (cdddr exp)))
(cadddr exp)
'false))
(define (begin? exp) (tagged-list? exp 'begin))
(define (begin-actions exp) (cdr exp))
(define (last-exp? seq) (null? (cdr seq)))
(define (first-exp seq) (car seq))
(define (rest-exps seq) (cdr seq))
(define (application? exp) (pair? exp))
(define (operator exp) (car exp))
(define (operands exp) (cdr exp))
(define (no-operands? ops) (null? ops))
(define (first-operand ops) (car ops))
(define (rest-operands ops) (cdr ops))
;;;**following needed only to implement COND as derived expression,
;;; not needed by eceval machine in text. But used by compiler
;; from 4.1.2
(define (make-if predicate consequent alternative)
(list 'if predicate consequent alternative))
(define (sequence->exp seq)
(cond ((null? seq) seq)
((last-exp? seq) (first-exp seq))
(else (make-begin seq))))
(define (make-begin seq) (cons 'begin seq))
(define (cond? exp) (tagged-list? exp 'cond))
(define (cond-clauses exp) (cdr exp))
(define (cond-else-clause? clause)
(eq? (cond-predicate clause) 'else))
(define (cond-predicate clause) (car clause))
(define (cond-actions clause) (cdr clause))
(define (cond->if exp)
(expand-clauses (cond-clauses exp)))
(define (expand-clauses clauses)
(if (null? clauses)
'false ; no else clause
(let ((first (car clauses))
(rest (cdr clauses)))
(if (cond-else-clause? first)
(if (null? rest)
(sequence->exp (cond-actions first))
(error "ELSE clause isn't last -- COND->IF"
clauses))
(make-if (cond-predicate first)
(sequence->exp (cond-actions first))
(expand-clauses rest))))))
;; end of Cond support