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+#lang sicp
+(#%require (only racket/base print-as-expression print-mpair-curly-braces))
+(print-as-expression #f)
+(print-mpair-curly-braces #f)
+
+;; Chapter 5
+;; Computing with Register Machines
+
+;; 5.4
+;; The Explicit-Control Evaluator
+
+;; The Core of the Explicit-Control Evaluator
+
+(define eval-dispatch
+  '(eval-dispatch
+      (test (op self-evaluating?) (reg exp))
+      (branch (label ev-self-eval))
+      (test (op variable?) (reg exp))
+      (branch (label ev-variable))
+      (test (op quoted?) (reg exp))
+      (branch (label ev-quoted))
+      (test (op assignment?) (reg exp))
+      (branch (label ev-assignment))
+      (test (op definition?) (reg exp))
+      (branch (label ev-definition))
+      (test (op if?) (reg exp))
+      (branch (label ev-if))
+      (test (op lambda?) (reg exp))
+      (branch (label ev-lambda))
+      (test (op begin?) (reg exp))
+      (branch (label ev-begin))
+      (test (op application?) (reg exp))
+      (branch (label ev-application))
+      (goto (label unknown-expression-type))))
+
+(define ev-self-eval
+  '(ev-self-eval
+      (assign val (reg exp))
+      (goto (reg continue))))
+
+(define ev-variable
+  '(ev-variable
+      (assign val (op lookup-variable-value) (reg exp) (reg env))
+      (goto (reg continue))))
+
+(define ev-quoted
+  '(ev-quoted
+      (assign val (op text-of-quotation) (reg exp))
+      (goto (reg continue))))
+
+(define ev-lambda
+  '(ev-lambda
+      (assign unev (op lambda-parameters) (reg exp))
+      (assign exp (op lambda-body) (reg exp))
+      (assign val (op make-procedure) (reg unev) (reg exp) (reg env))
+      (goto (reg continue))))
+
+(define (empty-arglist) '())
+
+(define (adjoin-arg arg arglist)
+  (append arglist (list arg)))
+
+(define (last-operand? ops)
+  (null? (cdr ops)))
+
+(define ev-application
+  '(ev-application
+      (save continue)
+      (save env)
+      (assign unev (op operands) (reg exp))
+      (save unev)
+      (assign exp (op operator) (reg exp))
+      (assign continue (label ev-appl-did-operator))
+      (goto (label eval-dispatch))
+    ev-appl-did-operator
+      (restore unev)
+      (restore env)
+      (assign argl (op empty-arglist))
+      (assign proc (reg val))
+      (test (op no-operands?) (reg unev))
+      (branch (label apply-dispatch))
+      (save proc)
+    ev-appl-operand-loop
+      (save argl)
+      (assign exp (op first-operand) (reg unev))
+      (test (op last-operand?) (reg unev))
+      (branch (label ev-appl-last-arg))
+      (save env)
+      (save unev)
+      (assign continue (label ev-appl-accumulate-arg))
+      (goto (label eval-dispatch))
+    ev-appl-accumulate-arg
+      (restore unev)
+      (restore env)
+      (restore argl)
+      (assign argl (op adjoin-arg) (reg val) (reg argl))
+      (assign unev (op rest-operands) (reg unev))
+      (goto (label ev-appl-operand-loop))
+    ev-appl-last-arg
+      (assign continue (label appl-accum-last-arg))
+      (goto (label eval-dispatch))
+    ev-appl-accum-last-arg
+      (restore argl)
+      (assign argl (op adjoin-arg) (reg val) (reg argl))
+      (restore proc)
+      (goto (label apply-dispatch))))
+
+(define apply-dispatch
+  '(apply-dispatch
+      (test (op primitive-procedure?) (reg proc))
+      (branch (label primitive-apply))
+      (test (op compound-procedure?) (reg proc))
+      (branch (label compound-apply))
+      (goto (label unknown-procedure-type))
+    primitive-apply
+      (assign val (op apply-primitive-procedure) (reg proc) (reg argl))
+      (restore continue)
+      (goto (reg continue))
+    compound-apply
+      (assign unev (op procedure-parameters) (reg proc))
+      (assign env (op procedure-environment) (reg proc))
+      (assign env (op extend-environment) (reg unev) (reg argl) (reg env))
+      (assign unev (op procedure-body) (reg proc))
+      (goto (label ev-sequence))))
+
+(define ev-begin
+  '(ev-begin
+      (assign unev (op begin-actions) (reg exp))
+      (save continue)
+      (goto (label ev-sequence))))
+
+;; Sequence Evaluation and Tail Recursion
+
+(define ev-sequence
+  '(ev-sequence
+      (assign exp (op first-exp) (reg unev))
+      (test (op last-exp?) (reg unev))
+      (branch (label ev-sequence-last-exp))
+      (save unev)
+      (save env)
+      (assign continue (label ev-sequence-continue))
+      (goto (label eval-dispatch))
+    ev-sequence-continue
+      (restore env)
+      (restore unev)
+      (assign unev (op rest-exps) (reg unev))
+      (goto (label ev-sequence))
+    ev-sequence-last-exp
+      (restore continue)
+      (goto (label eval-dispatch))))
+
+(define (no-more-exps? seq) (null? seq))
+
+(define ev-sequence-bad
+  '(ev-sequence
+      (test (op no-more-exps) (reg unev))
+      (branch (label ev-sequence-end))
+      (assign exp (op first-exp) (reg unev))
+      (save unev)
+      (save env)
+      (assign continue (label ev-sequence-continue))
+      (goto (label eval-dispatch))
+    ev-sequence-continue
+      (restore env)
+      (restore unev)
+      (assign unev (op rest-exps) (reg unev))
+      (goto (label ev-sequence))
+    ev-sequence-end
+      (restore continue)
+      (goto (label continue))))
+
+(#%provide count)
+(define (count n)
+  (newline)
+  (display n)
+  (count (+ n 1)))
+
+;; Conditionals, Assignments, and Definitions
+
+(define ev-if
+  '(ev-if
+      (save exp)
+      (save env)
+      (save continue)
+      (assign continue (label ev-if-decide))
+      (assign exp (op if-predicate) (reg exp))
+      (goto (label eval-dispatch))
+    ev-if-decide
+      (restore continue)
+      (restore env)
+      (test (op true?) (reg val))
+      (branch (label ev-if-consequent))
+    ev-if-alternative
+      (assign exp (op if-alternative) (reg exp))
+      (goto (label eval-dispatch))
+    ev-if-consequent
+      (assign exp (op if-consequent) (reg exp))
+      (goto (label eval-dispatch))))
+
+(define ev-assignment
+  '(ev-assignment
+      (assign unev (op assignment-variable) (reg exp))
+      (save unev)
+      (assign exp (op assignment-value) (reg exp))
+      (save env)
+      (save continue)
+      (assign continue (label ev-assignment-1))
+      (goto (label eval-dispatch))
+    ev-assignment-1
+      (restore continue)
+      (restore env)
+      (restore unev)
+      (perform (op set-variable-value!) (reg unev) (reg val) (reg env))
+      (assign val (const ok))
+      (goto (reg continue))))
+
+(define ev-definition
+  '(ev-definition
+      (assign unev (op definition-variable) (reg exp))
+      (save unev)
+      (assign exp (op definition-value) (reg exp))
+      (save env)
+      (save continue)
+      (assign continue (label ev-definition-1))
+    ev-definition-1
+      (restore continue)
+      (restore env)
+      (restore unev)
+      (perform (op define-variable!) (reg unev) (reg val) (reg env))
+      (assign val (const ok))
+      (goto (reg continue))))
+
+(define read-eval-print-loop
+  '(read-eval-print-loop
+      (perform (op initialize-stack))
+      (perform (op prompt-for-input) (const ";;; EC-Eval input:"))
+      (assign exp (op read))
+      (assign env (op get-global-environment))
+      (assign continue (label print-result))
+      (goto (label eval-dispatch))
+    print-result
+      (perform (op announce-output) (const ";;; EC-Eval value:"))
+      (perform (op user-print) (reg val))
+      (goto (label read-eval-print-loop))))
+
+(define errors
+  '(unknown-expression-type
+      (assign val (const unknown-expression-type-error))
+      (goto (label signal-error))
+    unknown-procedure-type
+      (restore continue)
+      (assign val (const unknown-procedure-type-error))
+      (goto (label signal-error))
+    signal-error
+      (perform (op user-print) (reg val))
+      (goto (label read-eval-print-loop))))
+
+(define (flatten xss)
+  (if (null? xss)
+    '()
+    (append
+      (car xss)
+      (flatten (cdr xss)))))
+
+(#%provide ec-eval-controller)
+(define ec-eval-controller
+  (flatten
+    (list
+      eval-dispatch
+      ev-self-eval
+      ev-variable
+      ev-quoted
+      ev-lambda
+      ev-application
+      apply-dispatch
+      ev-begin
+      ev-sequence
+      ev-sequence-bad
+      ev-if
+      ev-assignment
+      ev-definition
+      read-eval-print-loop
+      errors)))
+
+#| 5.23 |#
+#| 5.24 |#
+#| 5.25 |#
+
+;; Running the Evaluator
+
+#| 5.26 |#
+#| 5.27 |#
+#| 5.28 |#
+#| 5.29 |#
+#| 5.30 |#
+
+(define (self-evaluating? exp)
+  (cond
+    ((number? exp) true)
+    ((string? exp) true)
+    (else false)))
+
+(define (variable? exp) (symbol? exp))
+
+(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 (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-predicate clause)
+  (car clause))
+
+(define (cond-else-clause? clause)
+  (eq? (cond-predicate clause) 'else))
+
+(define (cond-actions clause) (cdr clause))
+
+(define (cond->if exp)
+  (expand-clauses (cond-clauses exp)))
+
+(define (expand-clauses clauses)
+  (if (null? clauses)
+    'false
+    (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))))))
+
+(define (let? exp) (tagged-list? exp 'let))
+
+(define (binding-var binding)
+  (car binding))
+
+(define (binding-exp binding)
+  (cadr binding))
+
+(define (let-bindings exp)
+  (cadr exp))
+
+(define (let-body exp)
+  (cddr exp))
+
+(define (let->combination exp)
+  (if (null? (let-bindings exp))
+    (if (null? (cdr (let-body exp)))
+      (car (let-body exp))
+      (cons 'begin (let-body exp)))
+    (cons
+      (cons
+        'lambda
+        (cons
+          (map binding-var (let-bindings exp))
+          (let-body exp)))
+      (map binding-exp (let-bindings exp)))))
+
+(define (true? x)
+  (not (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" 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))))
+
+(define (get-value binding)
+  (cdr binding))
+
+(define (set-value! val)
+  (lambda (binding)
+    (set-cdr! binding val)))
+
+(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 'cdr cdr)
+    (list 'cons cons)
+    (list 'null? null?)
+    (list '+ +)
+    (list '- -)
+    (list '* *)
+    (list '/ /)
+    (list '> >)
+    (list '< <)
+    (list '= =)
+    (list '<= <=)
+    (list '>= >=)))
+
+(define (primitive-procedure-names)
+  (map car primitive-procedures))
+
+(define (primitive-procedure-objects)
+  (map
+    (lambda (proc) (list 'primitive (cadr proc)))
+    primitive-procedures))
+
+(define (apply-primitive-procedure proc args)
+  (apply
+    (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)))