Implement 5.50 compiled meta-circular evaluator executed by regsim

ex-5_50-52.scm

@@ -1,24 +1,88 @@
 (load "shared/util")
-(load "shared/sicp-load-eceval-compiler")
+(load "shared/ch5-regsim")
-(load "shared/sicp-compiler")
+(load "shared/ch5-compiler")
+(load "shared/ch5-eceval-support")
 
 (display "\nex-5.50 - compile-metacircular-evaluator\n")
 
-; Exercise 5.50.  Use the compiler to compile the metacircular evaluator of
+(define mceval-code
-; section 4.1 and run this program using the register-machine simulator. (To
+  (let ((port (open-input-file "shared/ch4-mceval.scm")))
-; compile more than one definition at a time, you can package the definitions
+    (read port)))
-; in a begin.) The resulting interpreter will run very slowly because of the
-; multiple levels of interpretation, but getting all the details to work is an
-; instructive exercise.
 
-(compile-and-go
+(define mceval-compiled
- '(begin
+  (append
-    (define (factorial n)
+    (list '(assign env (op get-global-environment)))
-      (if (= n 1)
+    (statements (compile mceval-code 'val 'next))))
-        1
+
-        (* (factorial (- n 1)) n)))
+;; write assembly to file for debug purposes
-    (factorial 10)))
+; (let ((port (open-output-file "f-mceval-compiled.scm")))
+;   (define (write-list-to-port xs port)
+;     (if (null? xs) '()
+;       (begin (display (car xs) port) (display "\n" port)
+;              (write-list-to-port (cdr xs) port))))
+;   (write-list-to-port mceval-compiled port)
+;   (close-output-port port))
+
+(define eceval-operations (list
+   (list 'list list)
+   (list 'cons cons)
+
+   (list 'true? true?)
+   (list 'false? false?)    ;for compiled code
+   (list 'make-procedure make-procedure)
+   (list 'compound-procedure? compound-procedure?)
+   (list 'procedure-parameters procedure-parameters)
+   (list 'procedure-body procedure-body)
+   (list 'procedure-environment procedure-environment)
+   (list 'extend-environment extend-environment)
+   (list 'lookup-variable-value lookup-variable-value)
+   (list 'set-variable-value! set-variable-value!)
+   (list 'define-variable! define-variable!)
+   (list 'primitive-procedure? primitive-procedure?)
+   (list 'apply-primitive-procedure apply-primitive-procedure)
+   (list 'prompt-for-input prompt-for-input)
+   (list 'announce-output announce-output)
+   (list 'user-print user-print)
+   (list 'empty-arglist empty-arglist)
+   (list 'adjoin-arg adjoin-arg)
+   (list 'last-operand? last-operand?)
+   (list 'no-more-exps? no-more-exps?)  ;for non-tail-recursive machine
+   (list 'get-global-environment get-global-environment)
+
+   ;;for compiled code (also in eceval-support.scm)
+   (list 'make-compiled-procedure make-compiled-procedure)
+   (list 'compiled-procedure? compiled-procedure?)
+   (list 'compiled-procedure-entry compiled-procedure-entry)
+   (list 'compiled-procedure-env compiled-procedure-env)
+  ))
+
+(define the-global-environment (setup-environment))
+(define mceval-machine
+  (make-machine
+    '(exp env val proc argl continue unev)
+    eceval-operations
+    mceval-compiled))
+
+(start mceval-machine)
+;; (factorial 5) computed by compiled mceval executed by register simulator
+(assert (get-register-contents mceval-machine 'val) 120)
+
+;; Uncomment driver loop within shared/ch4-mceval.scm and load in mit-scheme
+;; for REPL:
+
+; λ symposium sicp → λ git master* → mit-scheme
+; 1 ]=> (load "ex-5_50-52")
+; ;;; M-Eval input:
+; (define (f n) (if (= n 1) 1 (* n (f (- n 1)))))
+; ;;; M-Eval value:
+; ok
+; ;;; M-Eval input:
+; (f 10)
+; ;;; M-Eval value:
+; 3628800
+; #magic
 
 (display "\nex-5.51\n")
 
-(display "\nex-5.52\n")
+;(display "\nex-5.52\n")
+

shared/ch4-mceval.scm

@@ -0,0 +1,369 @@
+;;;;METACIRCULAR EVALUATOR FROM CHAPTER 4 (SECTIONS 4.1.1-4.1.4) of
+;;;; STRUCTURE AND INTERPRETATION OF COMPUTER PROGRAMS
+
+;;;;Matches code in ch4.scm
+
+;;;;This file can be loaded into Scheme as a whole.
+;;;;Then you can initialize and start the evaluator by evaluating
+;;;; the two commented-out lines at the end of the file (setting up the
+;;;; global environment and starting the driver loop).
+
+;;;;**WARNING: Don't load this file twice (or you'll lose the primitives
+;;;;  interface, due to renamings of apply).
+
+;;;from section 4.1.4 -- must precede def of metacircular apply
+
+(begin
+  (define apply-in-underlying-scheme apply)
+
+  ;;;SECTION 4.1.1
+
+  (define (eval exp env)
+    (cond ((self-evaluating? exp) exp)
+          ((variable? exp) (lookup-variable-value exp env))
+          ((quoted? exp) (text-of-quotation exp))
+          ((assignment? exp) (eval-assignment exp env))
+          ((definition? exp) (eval-definition exp env))
+          ((if? exp) (eval-if exp env))
+          ((lambda? exp)
+           (make-procedure (lambda-parameters exp)
+                           (lambda-body exp)
+                           env))
+          ((begin? exp)
+           (eval-sequence (begin-actions exp) env))
+          ((cond? exp) (eval (cond->if exp) env))
+          ((application? exp)
+           (apply (eval (operator exp) env)
+                  (list-of-values (operands exp) env)))
+          (else
+           (error "Unknown expression type -- EVAL" exp))))
+
+  (define (apply procedure arguments)
+    (cond ((primitive-procedure? procedure)
+           (apply-primitive-procedure procedure arguments))
+          ((compound-procedure? procedure)
+           (eval-sequence
+             (procedure-body procedure)
+             (extend-environment
+               (procedure-parameters procedure)
+               arguments
+               (procedure-environment procedure))))
+          (else
+           (error
+            "Unknown procedure type -- APPLY" procedure))))
+
+
+  (define (list-of-values exps env)
+    (if (no-operands? exps)
+        '()
+        (cons (eval (first-operand exps) env)
+              (list-of-values (rest-operands exps) env))))
+
+  (define (eval-if exp env)
+    (if (true? (eval (if-predicate exp) env))
+        (eval (if-consequent exp) env)
+        (eval (if-alternative exp) env)))
+
+  (define (eval-sequence exps env)
+    (cond ((last-exp? exps) (eval (first-exp exps) env))
+          (else (eval (first-exp exps) env)
+                (eval-sequence (rest-exps exps) env))))
+
+  (define (eval-assignment exp env)
+    (set-variable-value! (assignment-variable exp)
+                         (eval (assignment-value exp) env)
+                         env)
+    'ok)
+
+  (define (eval-definition exp env)
+    (define-variable! (definition-variable exp)
+                      (eval (definition-value exp) env)
+                      env)
+    'ok)
+
+  ;;;SECTION 4.1.2
+
+  (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 (make-if predicate consequent alternative)
+    (list 'if predicate consequent alternative))
+
+
+  (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 (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 (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))
+
+
+  (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))))))
+
+  ;;;SECTION 4.1.3
+
+  (define (true? x)
+    (not (eq? x false)))
+
+  (define (false? x)
+    (eq? x false))
+
+
+  (define (make-procedure parameters body env)
+    (list 'procedure parameters body env))
+
+  (define (compound-procedure? p)
+    (tagged-list? p 'procedure))
+
+
+  (define (procedure-parameters p) (cadr p))
+  (define (procedure-body p) (caddr p))
+  (define (procedure-environment p) (cadddr p))
+
+
+  (define (enclosing-environment env) (cdr env))
+
+  (define (first-frame env) (car env))
+
+  (define the-empty-environment '())
+
+  (define (make-frame variables values)
+    (cons variables values))
+
+  (define (frame-variables frame) (car frame))
+  (define (frame-values frame) (cdr frame))
+
+  (define (add-binding-to-frame! var val frame)
+    (set-car! frame (cons var (car frame)))
+    (set-cdr! frame (cons val (cdr frame))))
+
+  (define (extend-environment vars vals base-env)
+    (if (= (length vars) (length vals))
+        (cons (make-frame vars vals) base-env)
+        (if (< (length vars) (length vals))
+            (error "Too many arguments supplied" vars vals)
+            (error "Too few arguments supplied" vars vals))))
+
+  (define (lookup-variable-value var env)
+    (define (env-loop env)
+      (define (scan vars vals)
+        (cond ((null? vars)
+               (env-loop (enclosing-environment env)))
+              ((eq? var (car vars))
+               (car vals))
+              (else (scan (cdr vars) (cdr vals)))))
+      (if (eq? env the-empty-environment)
+          (error "Unbound variable" var)
+          (let ((frame (first-frame env)))
+            (scan (frame-variables frame)
+                  (frame-values frame)))))
+    (env-loop env))
+
+  (define (set-variable-value! var val env)
+    (define (env-loop env)
+      (define (scan vars vals)
+        (cond ((null? vars)
+               (env-loop (enclosing-environment env)))
+              ((eq? var (car vars))
+               (set-car! vals val))
+              (else (scan (cdr vars) (cdr vals)))))
+      (if (eq? env the-empty-environment)
+          (error "Unbound variable -- SET!" var)
+          (let ((frame (first-frame env)))
+            (scan (frame-variables frame)
+                  (frame-values frame)))))
+    (env-loop env))
+
+  (define (define-variable! var val env)
+    (let ((frame (first-frame env)))
+      (define (scan vars vals)
+        (cond ((null? vars)
+               (add-binding-to-frame! var val frame))
+              ((eq? var (car vars))
+               (set-car! vals val))
+              (else (scan (cdr vars) (cdr vals)))))
+      (scan (frame-variables frame)
+            (frame-values frame))))
+
+  ;;;SECTION 4.1.4
+
+  (define (setup-environment)
+    (let ((initial-env
+           (extend-environment (primitive-procedure-names)
+                               (primitive-procedure-objects)
+                               the-empty-environment)))
+      (define-variable! 'true true initial-env)
+      (define-variable! 'false false initial-env)
+      initial-env))
+
+  ;[do later] (define the-global-environment (setup-environment))
+
+  (define (primitive-procedure? proc)
+    (tagged-list? proc 'primitive))
+
+  (define (primitive-implementation proc) (cadr proc))
+
+  (define primitive-procedures
+    (list (list 'car car)
+          (list 'cdr cdr)
+          (list '+ +)
+          (list '- -)
+          (list '= =)
+          (list '* *)
+          (list 'cons cons)
+          (list 'null? null?)
+          ))
+
+  (define (primitive-procedure-names)
+    (map car
+         primitive-procedures))
+
+  (define (primitive-procedure-objects)
+    (map (lambda (proc) (cadr proc))
+         primitive-procedures))
+
+  ;[moved to start of file] (define apply-in-underlying-scheme apply)
+
+  (define (apply-primitive-procedure proc args)
+    (apply-in-underlying-scheme
+     (primitive-implementation proc) args))
+
+
+
+  (define input-prompt ";;; M-Eval input:")
+  (define output-prompt ";;; M-Eval value:")
+
+  (define (driver-loop)
+    (prompt-for-input input-prompt)
+    (let ((input (read)))
+      (let ((output (eval input the-global-environment)))
+        (announce-output output-prompt)
+        (user-print output)))
+    (driver-loop))
+
+  (define (prompt-for-input string)
+    (newline) (newline) (display string) (newline))
+
+  (define (announce-output string)
+    (newline) (display string) (newline))
+
+  (define (user-print object)
+    (if (compound-procedure? object)
+        (display (list 'compound-procedure
+                       (procedure-parameters object)
+                       (procedure-body object)
+                       '<procedure-env>))
+        (display object)))
+
+;  ;;;Following are commented out so as not to be evaluated when
+;  ;;; the file is loaded.
+  (define (map f xs)
+    (if (null? xs)
+      (list)
+      (cons (f (car xs)) (map f (cdr xs)))))
+
+  (define the-global-environment (setup-environment))
+  (eval '(begin
+          (define (f n) (if (= n 1) 1 (* n (f (- n 1)))))
+          (f 5)) the-global-environment)
+  ;(driver-loop)
+)

shared/ch5-compiler.scm

@@ -0,0 +1,397 @@
+;;;;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 "shared/ch5-syntax")      ;section 4.1.2 syntax procedures
+
+
+;;;SECTION 5.5.1
+
+
+(define (let? exp) (tagged-list? exp 'let))
+(define (let-bindings exp) (cadr exp))
+(define (let-body exp) (cddr exp))
+(define (let-binding-var binding) (car binding))
+(define (let-binding-exp binding) (cadr binding))
+(define (let-vars exp) (map let-binding-var (let-bindings exp)))
+(define (let-exps exp) (map let-binding-exp (let-bindings exp)))
+
+(define (let->combination exp)
+  (let ((let-variables (let-vars exp))
+        (let-expressions (let-exps exp)))
+    (cons (make-lambda let-variables (let-body exp))
+          let-expressions)))
+
+
+(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))
+        ((let? exp) (compile (let->combination 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)

shared/ch5-eceval-support.scm

@@ -0,0 +1,211 @@
+;;;;SIMULATION OF ECEVAL MACHINE OPERATIONS --
+;;;;loaded by load-eceval.scm and by load-eceval-compiler.scm
+
+;;;;FIRST A LOT FROM 4.1.2-4.1.4
+
+(load "shared/ch5-syntax.scm");               ;section 4.1.2 syntax procedures
+
+;;;SECTION 4.1.3
+;;; operations used by compiled code and eceval except as noted
+
+(define (true? x)
+  (not (eq? x false)))
+
+;;* not used by eceval itself -- used by compiled code when that
+;; is run in the eceval machine
+(define (false? x)
+  (eq? x false))
+
+;;following compound-procedure operations not used by compiled code
+(define (make-procedure parameters body env)
+  (list 'procedure parameters body env))
+
+(define (compound-procedure? p)
+  (tagged-list? p 'procedure))
+
+(define (procedure-parameters p) (cadr p))
+(define (procedure-body p) (caddr p))
+(define (procedure-environment p) (cadddr p))
+;;(end of compound procedures)
+
+
+(define (enclosing-environment env) (cdr env))
+
+(define (first-frame env) (car env))
+
+(define the-empty-environment '())
+
+(define (make-frame variables values)
+  (cons variables values))
+
+(define (frame-variables frame) (car frame))
+(define (frame-values frame) (cdr frame))
+
+(define (add-binding-to-frame! var val frame)
+  (set-car! frame (cons var (car frame)))
+  (set-cdr! frame (cons val (cdr frame))))
+
+(define (extend-environment vars vals base-env)
+  (if (= (length vars) (length vals))
+      (cons (make-frame vars vals) base-env)
+      (if (< (length vars) (length vals))
+          (error "Too many arguments supplied" vars vals)
+          (error "Too few arguments supplied" vars vals))))
+
+
+(define (lookup-variable-value var env)
+  (define (env-loop env)
+    (define (scan vars vals)
+      (cond ((null? vars)
+             (env-loop (enclosing-environment env)))
+            ((eq? var (car vars))
+             (car vals))
+            (else (scan (cdr vars) (cdr vals)))))
+    (if (eq? env the-empty-environment)
+        (error "Unbound variable" var)
+        (let ((frame (first-frame env)))
+          (scan (frame-variables frame)
+                (frame-values frame)))))
+  (env-loop env))
+
+(define (set-variable-value! var val env)
+  (define (env-loop env)
+    (define (scan vars vals)
+      (cond ((null? vars)
+             (env-loop (enclosing-environment env)))
+            ((eq? var (car vars))
+             (set-car! vals val))
+            (else (scan (cdr vars) (cdr vals)))))
+    (if (eq? env the-empty-environment)
+        (error "Unbound variable -- SET!" var)
+        (let ((frame (first-frame env)))
+          (scan (frame-variables frame)
+                (frame-values frame)))))
+  (env-loop env))
+
+(define (define-variable! var val env)
+  (let ((frame (first-frame env)))
+    (define (scan vars vals)
+      (cond ((null? vars)
+             (add-binding-to-frame! var val frame))
+            ((eq? var (car vars))
+             (set-car! vals val))
+            (else (scan (cdr vars) (cdr vals)))))
+    (scan (frame-variables frame)
+          (frame-values frame))))
+
+
+;;;SECTION 4.1.4
+
+(define (setup-environment)
+  (let ((initial-env
+         (extend-environment (primitive-procedure-names)
+                             (primitive-procedure-objects)
+                             the-empty-environment)))
+    (define-variable! 'true true initial-env)
+    (define-variable! 'false false initial-env)
+    initial-env))
+
+(define (primitive-procedure? proc)
+  (tagged-list? proc 'primitive))
+
+(define (primitive-implementation proc) (cadr proc))
+
+(define primitive-procedures
+  (list (list 'car car)
+        (list 'cadr cadr)
+        (list 'caddr caddr)
+        (list 'cadddr cadddr)
+        (list 'caadr caadr)
+        (list 'cdr cdr)
+        (list 'cddr cddr)
+        (list 'cdddr cdddr)
+        (list 'cdadr cdadr)
+        (list 'cons cons)
+        (list 'eq? eq?)
+        (list 'length length)
+        (list 'list list)
+        (list 'null? null?)
+        (list 'number? number?)
+        (list 'pair? pair?)
+        (list 'set-car! set-car!)
+        (list 'set-cdr! set-cdr!)
+        (list 'string? string?)
+        (list 'symbol? symbol?)
+        ;;above from book -- here are some more
+        (list '+ +)
+        (list '- -)
+        (list '* *)
+        (list '= =)
+        (list '/ /)
+        (list '> >)
+        (list '< <)
+        (list 'apply apply)
+        (list 'not not)
+
+       ;; for driver loop and debugging
+       (list 'display display)
+       (list 'newline newline)
+       (list 'error error)
+       (list 'read read)
+        ))
+
+(define (primitive-procedure-names)
+  (map car
+       primitive-procedures))
+
+(define (primitive-procedure-objects)
+  (map (lambda (proc) (list 'primitive (cadr proc)))
+       primitive-procedures))
+
+(define apply-in-underlying-scheme apply)
+
+(define (apply-primitive-procedure proc args)
+  (apply-in-underlying-scheme
+   (primitive-implementation proc) args))
+
+
+(define (prompt-for-input string)
+  (newline) (newline) (display string) (newline))
+
+(define (announce-output string)
+  (newline) (display string) (newline))
+
+(define (user-print object)
+  (if (compound-procedure? object)
+      (display (list 'compound-procedure
+                     (procedure-parameters object)
+                     (procedure-body object)
+                     '<procedure-env>))
+      (display object)))
+
+;;; Simulation of new machine operations needed by
+;;;  eceval machine (not used by compiled code)
+
+;;; From section 5.4.1 footnote
+(define (empty-arglist) '())
+(define (adjoin-arg arg arglist)
+  (append arglist (list arg)))
+(define (last-operand? ops)
+  (null? (cdr ops)))
+
+;;; From section 5.4.2 footnote, for non-tail-recursive sequences
+(define (no-more-exps? seq) (null? seq))
+
+;;; From section 5.4.4 footnote
+(define (get-global-environment)
+  the-global-environment)
+;; will do following when ready to run, not when load this file
+;;(define the-global-environment (setup-environment))
+
+
+;;; Simulation of new machine operations needed for compiled code
+;;;  and eceval/compiler interface (not used by plain eceval machine)
+;;; From section 5.5.2 footnote
+(define (make-compiled-procedure entry env)
+  (list 'compiled-procedure entry env))
+(define (compiled-procedure? proc)
+  (tagged-list? proc 'compiled-procedure))
+(define (compiled-procedure-entry c-proc) (cadr c-proc))
+(define (compiled-procedure-env c-proc) (caddr c-proc))
+

shared/ch5-regsim.scm

@@ -0,0 +1,407 @@
+;;;;REGISTER-MACHINE SIMULATOR FROM SECTION 5.2 OF
+;;;; STRUCTURE AND INTERPRETATION OF COMPUTER PROGRAMS
+
+;;;;Matches code in ch5.scm
+
+;;;;This file can be loaded into Scheme as a whole.
+;;;;Then you can define and simulate machines as shown in section 5.2
+
+;;;**NB** there are two versions of make-stack below.
+;;; Choose the monitored or unmonitored one by reordering them to put the
+;;;  one you want last, or by commenting one of them out.
+;;; Also, comment in/out the print-stack-statistics op in make-new-machine
+;;; To find this stack code below, look for comments with **
+
+
+(define (make-machine register-names ops controller-text)
+  (let ((machine (make-new-machine)))
+    (for-each (lambda (register-name)
+                ((machine 'allocate-register) register-name))
+              register-names)
+    ((machine 'install-operations) ops)    
+    ((machine 'install-instruction-sequence)
+     (assemble controller-text machine))
+    machine))
+
+(define (make-register name)
+  (let ((contents '*unassigned*))
+    (define (dispatch message)
+      (cond ((eq? message 'get) contents)
+            ((eq? message 'set)
+             (lambda (value) (set! contents value)))
+            (else
+             (error "Unknown request -- REGISTER" message))))
+    dispatch))
+
+(define (get-contents register)
+  (register 'get))
+
+(define (set-contents! register value)
+  ((register 'set) value))
+
+;;**original (unmonitored) version from section 5.2.1
+(define (make-stack)
+  (let ((s '()))
+    (define (push x)
+      (set! s (cons x s)))
+    (define (pop)
+      (if (null? s)
+          (error "Empty stack -- POP")
+          (let ((top (car s)))
+            (set! s (cdr s))
+            top)))
+    (define (initialize)
+      (set! s '())
+      'done)
+    (define (dispatch message)
+      (cond ((eq? message 'push) push)
+            ((eq? message 'pop) (pop))
+            ((eq? message 'initialize) (initialize))
+            (else (error "Unknown request -- STACK"
+                         message))))
+    dispatch))
+
+(define (pop stack)
+  (stack 'pop))
+
+(define (push stack value)
+  ((stack 'push) value))
+
+;;**monitored version from section 5.2.4
+(define (make-stack)
+  (let ((s '())
+        (number-pushes 0)
+        (max-depth 0)
+        (current-depth 0))
+    (define (push x)
+      (set! s (cons x s))
+      (set! number-pushes (+ 1 number-pushes))
+      (set! current-depth (+ 1 current-depth))
+      (set! max-depth (max current-depth max-depth)))
+    (define (pop)
+      (if (null? s)
+          (error "Empty stack -- POP")
+          (let ((top (car s)))
+            (set! s (cdr s))
+            (set! current-depth (- current-depth 1))
+            top)))    
+    (define (initialize)
+      (set! s '())
+      (set! number-pushes 0)
+      (set! max-depth 0)
+      (set! current-depth 0)
+      'done)
+    (define (print-statistics)
+      (newline)
+      (display (list 'total-pushes  '= number-pushes
+                     'maximum-depth '= max-depth)))
+    (define (dispatch message)
+      (cond ((eq? message 'push) push)
+            ((eq? message 'pop) (pop))
+            ((eq? message 'initialize) (initialize))
+            ((eq? message 'print-statistics)
+             (print-statistics))
+            (else
+             (error "Unknown request -- STACK" message))))
+    dispatch))
+
+(define (make-new-machine)
+  (let ((pc (make-register 'pc))
+        (flag (make-register 'flag))
+        (stack (make-stack))
+        (the-instruction-sequence '()))
+    (let ((the-ops
+           (list (list 'initialize-stack
+                       (lambda () (stack 'initialize)))
+                 ;;**next for monitored stack (as in section 5.2.4)
+                 ;;  -- comment out if not wanted
+                 (list 'print-stack-statistics
+                       (lambda () (stack 'print-statistics)))))
+          (register-table
+           (list (list 'pc pc) (list 'flag flag))))
+      (define (allocate-register name)
+        (if (assoc name register-table)
+            (error "Multiply defined register: " name)
+            (set! register-table
+                  (cons (list name (make-register name))
+                        register-table)))
+        'register-allocated)
+      (define (lookup-register name)
+        (let ((val (assoc name register-table)))
+          (if val
+              (cadr val)
+              (error "Unknown register:" name))))
+      (define (execute)
+        (let ((insts (get-contents pc)))
+          (if (null? insts)
+              'done
+              (begin
+                ((instruction-execution-proc (car insts)))
+                (execute)))))
+      (define (dispatch message)
+        (cond ((eq? message 'start)
+               (set-contents! pc the-instruction-sequence)
+               (execute))
+              ((eq? message 'install-instruction-sequence)
+               (lambda (seq) (set! the-instruction-sequence seq)))
+              ((eq? message 'allocate-register) allocate-register)
+              ((eq? message 'get-register) lookup-register)
+              ((eq? message 'install-operations)
+               (lambda (ops) (set! the-ops (append the-ops ops))))
+              ((eq? message 'stack) stack)
+              ((eq? message 'operations) the-ops)
+              (else (error "Unknown request -- MACHINE" message))))
+      dispatch)))
+
+
+(define (start machine)
+  (machine 'start))
+
+(define (get-register-contents machine register-name)
+  (get-contents (get-register machine register-name)))
+
+(define (set-register-contents! machine register-name value)
+  (set-contents! (get-register machine register-name) value)
+  'done)
+
+(define (get-register machine reg-name)
+  ((machine 'get-register) reg-name))
+
+(define (assemble controller-text machine)
+  (extract-labels controller-text
+    (lambda (insts labels)
+      (update-insts! insts labels machine)
+      insts)))
+
+(define (extract-labels text receive)
+  (if (null? text)
+      (receive '() '())
+      (extract-labels (cdr text)
+       (lambda (insts labels)
+         (let ((next-inst (car text)))
+           (if (symbol? next-inst)
+               (receive insts
+                        (cons (make-label-entry next-inst
+                                                insts)
+                              labels))
+               (receive (cons (make-instruction next-inst)
+                              insts)
+                        labels)))))))
+
+(define (update-insts! insts labels machine)
+  (let ((pc (get-register machine 'pc))
+        (flag (get-register machine 'flag))
+        (stack (machine 'stack))
+        (ops (machine 'operations)))
+    (for-each
+     (lambda (inst)
+       (set-instruction-execution-proc! 
+        inst
+        (make-execution-procedure
+         (instruction-text inst) labels machine
+         pc flag stack ops)))
+     insts)))
+
+(define (make-instruction text)
+  (cons text '()))
+
+(define (instruction-text inst)
+  (car inst))
+
+(define (instruction-execution-proc inst)
+  (cdr inst))
+
+(define (set-instruction-execution-proc! inst proc)
+  (set-cdr! inst proc))
+
+(define (make-label-entry label-name insts)
+  (cons label-name insts))
+
+(define (lookup-label labels label-name)
+  (let ((val (assoc label-name labels)))
+    (if val
+        (cdr val)
+        (error "Undefined label -- ASSEMBLE" label-name))))
+
+
+(define (make-execution-procedure inst labels machine
+                                  pc flag stack ops)
+  (cond ((eq? (car inst) 'assign)
+         (make-assign inst machine labels ops pc))
+        ((eq? (car inst) 'test)
+         (make-test inst machine labels ops flag pc))
+        ((eq? (car inst) 'branch)
+         (make-branch inst machine labels flag pc))
+        ((eq? (car inst) 'goto)
+         (make-goto inst machine labels pc))
+        ((eq? (car inst) 'save)
+         (make-save inst machine stack pc))
+        ((eq? (car inst) 'restore)
+         (make-restore inst machine stack pc))
+        ((eq? (car inst) 'perform)
+         (make-perform inst machine labels ops pc))
+        (else (error "Unknown instruction type -- ASSEMBLE"
+                     inst))))
+
+
+(define (make-assign inst machine labels operations pc)
+  (let ((target
+         (get-register machine (assign-reg-name inst)))
+        (value-exp (assign-value-exp inst)))
+    (let ((value-proc
+           (if (operation-exp? value-exp)
+               (make-operation-exp
+                value-exp machine labels operations)
+               (make-primitive-exp
+                (car value-exp) machine labels))))
+      (lambda ()                ; execution procedure for assign
+        (set-contents! target (value-proc))
+        (advance-pc pc)))))
+
+(define (assign-reg-name assign-instruction)
+  (cadr assign-instruction))
+
+(define (assign-value-exp assign-instruction)
+  (cddr assign-instruction))
+
+(define (advance-pc pc)
+  (set-contents! pc (cdr (get-contents pc))))
+
+(define (make-test inst machine labels operations flag pc)
+  (let ((condition (test-condition inst)))
+    (if (operation-exp? condition)
+        (let ((condition-proc
+               (make-operation-exp
+                condition machine labels operations)))
+          (lambda ()
+            (set-contents! flag (condition-proc))
+            (advance-pc pc)))
+        (error "Bad TEST instruction -- ASSEMBLE" inst))))
+
+(define (test-condition test-instruction)
+  (cdr test-instruction))
+
+
+(define (make-branch inst machine labels flag pc)
+  (let ((dest (branch-dest inst)))
+    (if (label-exp? dest)
+        (let ((insts
+               (lookup-label labels (label-exp-label dest))))
+          (lambda ()
+            (if (get-contents flag)
+                (set-contents! pc insts)
+                (advance-pc pc))))
+        (error "Bad BRANCH instruction -- ASSEMBLE" inst))))
+
+(define (branch-dest branch-instruction)
+  (cadr branch-instruction))
+
+
+(define (make-goto inst machine labels pc)
+  (let ((dest (goto-dest inst)))
+    (cond ((label-exp? dest)
+           (let ((insts
+                  (lookup-label labels
+                                (label-exp-label dest))))
+             (lambda () (set-contents! pc insts))))
+          ((register-exp? dest)
+           (let ((reg
+                  (get-register machine
+                                (register-exp-reg dest))))
+             (lambda ()
+               (set-contents! pc (get-contents reg)))))
+          (else (error "Bad GOTO instruction -- ASSEMBLE"
+                       inst)))))
+
+(define (goto-dest goto-instruction)
+  (cadr goto-instruction))
+
+(define (make-save inst machine stack pc)
+  (let ((reg (get-register machine
+                           (stack-inst-reg-name inst))))
+    (lambda ()
+      (push stack (get-contents reg))
+      (advance-pc pc))))
+
+(define (make-restore inst machine stack pc)
+  (let ((reg (get-register machine
+                           (stack-inst-reg-name inst))))
+    (lambda ()
+      (set-contents! reg (pop stack))    
+      (advance-pc pc))))
+
+(define (stack-inst-reg-name stack-instruction)
+  (cadr stack-instruction))
+
+(define (make-perform inst machine labels operations pc)
+  (let ((action (perform-action inst)))
+    (if (operation-exp? action)
+        (let ((action-proc
+               (make-operation-exp
+                action machine labels operations)))
+          (lambda ()
+            (action-proc)
+            (advance-pc pc)))
+        (error "Bad PERFORM instruction -- ASSEMBLE" inst))))
+
+(define (perform-action inst) (cdr inst))
+
+(define (make-primitive-exp exp machine labels)
+  (cond ((constant-exp? exp)
+         (let ((c (constant-exp-value exp)))
+           (lambda () c)))
+        ((label-exp? exp)
+         (let ((insts
+                (lookup-label labels
+                              (label-exp-label exp))))
+           (lambda () insts)))
+        ((register-exp? exp)
+         (let ((r (get-register machine
+                                (register-exp-reg exp))))
+           (lambda () (get-contents r))))
+        (else
+         (error "Unknown expression type -- ASSEMBLE" exp))))
+
+(define (register-exp? exp) (tagged-list? exp 'reg))
+
+(define (register-exp-reg exp) (cadr exp))
+
+(define (constant-exp? exp) (tagged-list? exp 'const))
+
+(define (constant-exp-value exp) (cadr exp))
+
+(define (label-exp? exp) (tagged-list? exp 'label))
+
+(define (label-exp-label exp) (cadr exp))
+
+
+(define (make-operation-exp exp machine labels operations)
+  (let ((op (lookup-prim (operation-exp-op exp) operations))
+        (aprocs
+         (map (lambda (e)
+                (make-primitive-exp e machine labels))
+              (operation-exp-operands exp))))
+    (lambda ()
+      (apply op (map (lambda (p) (p)) aprocs)))))
+
+(define (operation-exp? exp)
+  (and (pair? exp) (tagged-list? (car exp) 'op)))
+(define (operation-exp-op operation-exp)
+  (cadr (car operation-exp)))
+(define (operation-exp-operands operation-exp)
+  (cdr operation-exp))
+
+
+(define (lookup-prim symbol operations)
+  (let ((val (assoc symbol operations)))
+    (if val
+        (cadr val)
+        (error "Unknown operation -- ASSEMBLE" symbol))))
+
+;; from 4.1
+(define (tagged-list? exp tag)
+  (if (pair? exp)
+      (eq? (car exp) tag)
+      false))
+
+'(REGISTER SIMULATOR LOADED)

shared/ch5-syntax.scm

@@ -0,0 +1,120 @@
+;;;;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