1 665c255d 2023-08-04 jrmu (define apply-in-underlying-scheme apply)
3 665c255d 2023-08-04 jrmu (define (eval exp env)
4 665c255d 2023-08-04 jrmu (cond ((self-evaluating? exp) exp)
5 665c255d 2023-08-04 jrmu ((variable? exp) (lookup-variable-value exp env))
6 665c255d 2023-08-04 jrmu ((quoted? exp) (text-of-quotation exp))
7 665c255d 2023-08-04 jrmu ((assignment? exp) (eval-assignment exp env))
8 665c255d 2023-08-04 jrmu ((definition? exp) (eval-definition exp env))
9 665c255d 2023-08-04 jrmu ((unbound? exp) (eval-unbound exp env))
10 665c255d 2023-08-04 jrmu ((if? exp) (eval-if exp env))
11 665c255d 2023-08-04 jrmu ((and? exp) (eval-and exp env))
12 665c255d 2023-08-04 jrmu ((or? exp) (eval-or exp env))
13 665c255d 2023-08-04 jrmu ((lambda? exp)
14 665c255d 2023-08-04 jrmu (make-procedure (lambda-parameters exp)
15 665c255d 2023-08-04 jrmu (lambda-body exp)
17 665c255d 2023-08-04 jrmu ((begin? exp)
18 665c255d 2023-08-04 jrmu (eval-sequence (begin-actions exp) env))
19 665c255d 2023-08-04 jrmu ((cond? exp) (eval (cond->if exp) env))
20 665c255d 2023-08-04 jrmu ((let? exp) (eval (let->combination exp) env))
21 665c255d 2023-08-04 jrmu ((let*? exp) (eval (let*->nested-lets exp) env))
22 665c255d 2023-08-04 jrmu ((named-let? exp) (eval (named-let->combination exp) env))
23 665c255d 2023-08-04 jrmu ((do? exp) (eval (do->combination exp) env))
24 665c255d 2023-08-04 jrmu ((application? exp)
25 665c255d 2023-08-04 jrmu (apply (eval (operator exp) env)
26 665c255d 2023-08-04 jrmu (list-of-values (operands exp) env)))
28 665c255d 2023-08-04 jrmu (error "Unknown expression type -- EVAL" exp))))
29 665c255d 2023-08-04 jrmu (define (apply procedure arguments)
30 665c255d 2023-08-04 jrmu (cond ((primitive-procedure? procedure)
31 665c255d 2023-08-04 jrmu (apply-primitive-procedure procedure arguments))
32 665c255d 2023-08-04 jrmu ((compound-procedure? procedure)
33 665c255d 2023-08-04 jrmu (eval-sequence
34 665c255d 2023-08-04 jrmu (procedure-body procedure)
35 665c255d 2023-08-04 jrmu (extend-environment
36 665c255d 2023-08-04 jrmu (procedure-parameters procedure)
38 665c255d 2023-08-04 jrmu (procedure-environment procedure))))
41 665c255d 2023-08-04 jrmu "Unknown procedure type -- APPLY" procedure))))
43 665c255d 2023-08-04 jrmu (define (list-of-values exps env)
44 665c255d 2023-08-04 jrmu (if (no-operands? exps)
46 665c255d 2023-08-04 jrmu (cons (eval (first-operand exps) env)
47 665c255d 2023-08-04 jrmu (list-of-values (rest-operands exps) env))))
49 665c255d 2023-08-04 jrmu (define (tagged-list? exp tag)
50 665c255d 2023-08-04 jrmu (if (pair? exp)
51 665c255d 2023-08-04 jrmu (eq? (car exp) tag)
54 665c255d 2023-08-04 jrmu ;; self-evaluating/variable/quoted
55 665c255d 2023-08-04 jrmu (define (self-evaluating? exp)
56 665c255d 2023-08-04 jrmu (cond ((number? exp) true)
57 665c255d 2023-08-04 jrmu ((string? exp) true)
58 665c255d 2023-08-04 jrmu (else false)))
59 665c255d 2023-08-04 jrmu (define (variable? exp) (symbol? exp))
60 665c255d 2023-08-04 jrmu (define (quoted? exp)
61 665c255d 2023-08-04 jrmu (tagged-list? exp 'quote))
62 665c255d 2023-08-04 jrmu (define (text-of-quotation exp) (cadr exp))
64 665c255d 2023-08-04 jrmu ;; assignment/definition
65 665c255d 2023-08-04 jrmu (define (assignment? exp)
66 665c255d 2023-08-04 jrmu (tagged-list? exp 'set!))
67 665c255d 2023-08-04 jrmu (define (assignment-variable exp) (cadr exp))
68 665c255d 2023-08-04 jrmu (define (assignment-value exp) (caddr exp))
69 665c255d 2023-08-04 jrmu (define (definition? exp)
70 665c255d 2023-08-04 jrmu (tagged-list? exp 'define))
71 665c255d 2023-08-04 jrmu (define (definition-variable exp)
72 665c255d 2023-08-04 jrmu (if (symbol? (cadr exp))
74 665c255d 2023-08-04 jrmu (caadr exp)))
75 665c255d 2023-08-04 jrmu (define (definition-value exp)
76 665c255d 2023-08-04 jrmu (if (symbol? (cadr exp))
78 665c255d 2023-08-04 jrmu (make-lambda (cdadr exp) ; formal parameters
79 665c255d 2023-08-04 jrmu (cddr exp)))) ; body
80 665c255d 2023-08-04 jrmu (define (eval-assignment exp env)
81 665c255d 2023-08-04 jrmu (set-variable-value! (assignment-variable exp)
82 665c255d 2023-08-04 jrmu (eval (assignment-value exp) env)
85 665c255d 2023-08-04 jrmu (define (eval-definition exp env)
86 665c255d 2023-08-04 jrmu (define-variable! (definition-variable exp)
87 665c255d 2023-08-04 jrmu (eval (definition-value exp) env)
90 665c255d 2023-08-04 jrmu (define (make-definition var val)
91 665c255d 2023-08-04 jrmu `(define ,var ,val))
93 665c255d 2023-08-04 jrmu ;; make-unbound!
95 665c255d 2023-08-04 jrmu (define (unbound? exp)
96 665c255d 2023-08-04 jrmu (tagged-list? exp 'make-unbound!))
97 665c255d 2023-08-04 jrmu (define (unbound-var exp)
99 665c255d 2023-08-04 jrmu (define (eval-unbound exp env)
100 665c255d 2023-08-04 jrmu (remove-binding-from-frame! (unbound-var exp) (first-frame env)))
101 665c255d 2023-08-04 jrmu (define (remove-binding-from-frame! var frame)
102 665c255d 2023-08-04 jrmu (define (scan vars vals)
103 665c255d 2023-08-04 jrmu (cond ((null? (cdr vars))
104 665c255d 2023-08-04 jrmu (error "Binding not found -- REMOVE-BINDING-FROM-FRAME!" var))
105 665c255d 2023-08-04 jrmu ((eq? var (cadr vars))
106 665c255d 2023-08-04 jrmu (set-cdr! vars (cddr vars))
107 665c255d 2023-08-04 jrmu (set-cdr! vals (cddr vals)))
108 665c255d 2023-08-04 jrmu (else (scan (cdr vars) (cdr vals)))))
109 665c255d 2023-08-04 jrmu (let ((vars (frame-variables frame))
110 665c255d 2023-08-04 jrmu (vals (frame-values frame)))
111 665c255d 2023-08-04 jrmu (if (eq? var (car vars))
112 665c255d 2023-08-04 jrmu (begin (set-car! frame (cdr vars))
113 665c255d 2023-08-04 jrmu (set-cdr! frame (cdr vals)))
114 665c255d 2023-08-04 jrmu (scan vars vals))))
116 665c255d 2023-08-04 jrmu ;; if/and/or
117 665c255d 2023-08-04 jrmu (define (if? exp) (tagged-list? exp 'if))
118 665c255d 2023-08-04 jrmu (define (if-predicate exp) (cadr exp))
119 665c255d 2023-08-04 jrmu (define (if-consequent exp) (caddr exp))
120 665c255d 2023-08-04 jrmu (define (if-alternative exp)
121 665c255d 2023-08-04 jrmu (if (not (null? (cdddr exp)))
122 665c255d 2023-08-04 jrmu (cadddr exp)
124 665c255d 2023-08-04 jrmu (define (make-if predicate consequent alternative)
125 665c255d 2023-08-04 jrmu (list 'if predicate consequent alternative))
126 665c255d 2023-08-04 jrmu (define (eval-if exp env)
127 665c255d 2023-08-04 jrmu (if (true? (eval (if-predicate exp) env))
128 665c255d 2023-08-04 jrmu (eval (if-consequent exp) env)
129 665c255d 2023-08-04 jrmu (eval (if-alternative exp) env)))
131 665c255d 2023-08-04 jrmu (define (and? exp)
132 665c255d 2023-08-04 jrmu (tagged-list? exp 'and))
133 665c255d 2023-08-04 jrmu (define (and-clauses exp)
135 665c255d 2023-08-04 jrmu (define (or? exp)
136 665c255d 2023-08-04 jrmu (tagged-list? exp 'or))
137 665c255d 2023-08-04 jrmu (define (or-clauses exp)
139 665c255d 2023-08-04 jrmu (define (eval-and exp env)
140 665c255d 2023-08-04 jrmu (define (eval-clauses clauses)
141 665c255d 2023-08-04 jrmu (cond ((null? clauses) true)
142 665c255d 2023-08-04 jrmu ((null? (cdr clauses)) (eval (car clauses) env))
143 665c255d 2023-08-04 jrmu (else (and (eval (car clauses) env)
144 665c255d 2023-08-04 jrmu (eval-clauses (cdr clauses))))))
145 665c255d 2023-08-04 jrmu (eval-clauses (and-clauses exp)))
146 665c255d 2023-08-04 jrmu (define (eval-or exp env)
147 665c255d 2023-08-04 jrmu (define (eval-clauses clauses)
148 665c255d 2023-08-04 jrmu (if (null? clauses)
150 665c255d 2023-08-04 jrmu (or (eval (car clauses) env)
151 665c255d 2023-08-04 jrmu (eval-clauses (cdr clauses)))))
152 665c255d 2023-08-04 jrmu (eval-clauses (or-clauses exp)))
155 665c255d 2023-08-04 jrmu ;; lambda/let/let*
156 665c255d 2023-08-04 jrmu (define (lambda? exp) (tagged-list? exp 'lambda))
157 665c255d 2023-08-04 jrmu (define (lambda-parameters exp) (cadr exp))
158 665c255d 2023-08-04 jrmu (define (lambda-body exp) (cddr exp))
159 665c255d 2023-08-04 jrmu (define (make-lambda parameters body)
160 665c255d 2023-08-04 jrmu (cons 'lambda (cons parameters body)))
162 665c255d 2023-08-04 jrmu (define (make-let vars vals body)
164 665c255d 2023-08-04 jrmu (cons (map list vars vals)
166 665c255d 2023-08-04 jrmu (define (let? exp)
167 665c255d 2023-08-04 jrmu (and (tagged-list? exp 'let)
168 665c255d 2023-08-04 jrmu (not (symbol? (cadr exp)))))
169 665c255d 2023-08-04 jrmu (define (let-vars exp)
170 665c255d 2023-08-04 jrmu (map car (cadr exp)))
171 665c255d 2023-08-04 jrmu (define (let-vals exp)
172 665c255d 2023-08-04 jrmu (map cadr (cadr exp)))
173 665c255d 2023-08-04 jrmu (define (let-body exp)
174 665c255d 2023-08-04 jrmu (cddr exp))
175 665c255d 2023-08-04 jrmu (define (let->combination exp)
176 665c255d 2023-08-04 jrmu (make-application (make-lambda (let-vars exp) (let-body exp))
177 665c255d 2023-08-04 jrmu (let-vals exp)))
178 665c255d 2023-08-04 jrmu (define (named-let? exp)
179 665c255d 2023-08-04 jrmu (and (tagged-list? exp 'let)
180 665c255d 2023-08-04 jrmu (symbol? (cadr exp))))
181 665c255d 2023-08-04 jrmu (define (named-let-name exp)
182 665c255d 2023-08-04 jrmu (cadr exp))
183 665c255d 2023-08-04 jrmu (define (named-let-vars exp)
184 665c255d 2023-08-04 jrmu (map car (caddr exp)))
185 665c255d 2023-08-04 jrmu (define (named-let-vals exp)
186 665c255d 2023-08-04 jrmu (map cadr (caddr exp)))
187 665c255d 2023-08-04 jrmu (define (named-let-body exp)
188 665c255d 2023-08-04 jrmu (cdddr exp))
189 665c255d 2023-08-04 jrmu (define (named-let->combination exp)
190 665c255d 2023-08-04 jrmu (sequence->exp
191 665c255d 2023-08-04 jrmu (list (make-definition (named-let-name exp)
192 665c255d 2023-08-04 jrmu (make-lambda (named-let-vars exp)
193 665c255d 2023-08-04 jrmu (named-let-body exp)))
194 665c255d 2023-08-04 jrmu (make-application (named-let-name exp)
195 665c255d 2023-08-04 jrmu (named-let-vals exp)))))
196 665c255d 2023-08-04 jrmu (define (make-named-let name vars vals body)
199 665c255d 2023-08-04 jrmu (cons (map list vars vals)
202 665c255d 2023-08-04 jrmu (define (make-application op args)
203 665c255d 2023-08-04 jrmu (cons op args))
205 665c255d 2023-08-04 jrmu (define (let*? exp)
206 665c255d 2023-08-04 jrmu (tagged-list? exp 'let*))
207 665c255d 2023-08-04 jrmu (define let*-vars let-vars)
208 665c255d 2023-08-04 jrmu (define let*-vals let-vals)
209 665c255d 2023-08-04 jrmu (define let*-body let-body)
210 665c255d 2023-08-04 jrmu (define (let*->nested-lets exp)
211 665c255d 2023-08-04 jrmu (define (expand-lets vars vals)
212 665c255d 2023-08-04 jrmu (if (null? (cdr vars))
213 665c255d 2023-08-04 jrmu (make-let (list (car vars))
214 665c255d 2023-08-04 jrmu (list (car vals))
215 665c255d 2023-08-04 jrmu (let*-body exp))
216 665c255d 2023-08-04 jrmu (make-let (list (car vars))
217 665c255d 2023-08-04 jrmu (list (car vals))
218 665c255d 2023-08-04 jrmu (list (expand-lets (cdr vars) (cdr vals))))))
219 665c255d 2023-08-04 jrmu (let ((vars (let*-vars exp))
220 665c255d 2023-08-04 jrmu (vals (let*-vals exp)))
221 665c255d 2023-08-04 jrmu (if (null? vars)
222 665c255d 2023-08-04 jrmu (sequence->exp (let*-body exp))
223 665c255d 2023-08-04 jrmu (expand-lets vars vals))))
226 665c255d 2023-08-04 jrmu (define (do? exp)
227 665c255d 2023-08-04 jrmu (tagged-list? exp 'do))
228 665c255d 2023-08-04 jrmu (define (do-vars exp)
229 665c255d 2023-08-04 jrmu (map car (cadr exp)))
230 665c255d 2023-08-04 jrmu (define (do-inits exp)
231 665c255d 2023-08-04 jrmu (map cadr (cadr exp)))
232 665c255d 2023-08-04 jrmu (define (do-steps exp)
233 665c255d 2023-08-04 jrmu (map (lambda (var-init-step)
234 665c255d 2023-08-04 jrmu (if (null? (cddr var-init-step))
235 665c255d 2023-08-04 jrmu (car var-init-step)
236 665c255d 2023-08-04 jrmu (caddr var-init-step)))
237 665c255d 2023-08-04 jrmu (cadr exp)))
238 665c255d 2023-08-04 jrmu (define (do-test exp)
239 665c255d 2023-08-04 jrmu (caaddr exp))
240 665c255d 2023-08-04 jrmu (define (do-expressions exp)
241 665c255d 2023-08-04 jrmu (if (null? (cdaddr exp))
242 665c255d 2023-08-04 jrmu (caddr exp)
243 665c255d 2023-08-04 jrmu (cdaddr exp)))
244 665c255d 2023-08-04 jrmu (define (do-commands exp)
245 665c255d 2023-08-04 jrmu (cdddr exp))
246 665c255d 2023-08-04 jrmu (define (do->combination exp)
247 665c255d 2023-08-04 jrmu (make-named-let
249 665c255d 2023-08-04 jrmu (do-vars exp)
250 665c255d 2023-08-04 jrmu (do-inits exp)
253 665c255d 2023-08-04 jrmu (do-test exp)
254 665c255d 2023-08-04 jrmu (sequence->exp (do-expressions exp))
255 665c255d 2023-08-04 jrmu (sequence->exp
256 665c255d 2023-08-04 jrmu (append (do-commands exp)
257 665c255d 2023-08-04 jrmu (list (make-application
259 665c255d 2023-08-04 jrmu (do-steps exp)))))))))
262 665c255d 2023-08-04 jrmu ;; begin/sequence
263 665c255d 2023-08-04 jrmu (define (begin? exp) (tagged-list? exp 'begin))
264 665c255d 2023-08-04 jrmu (define (begin-actions exp) (cdr exp))
265 665c255d 2023-08-04 jrmu (define (last-exp? seq) (null? (cdr seq)))
266 665c255d 2023-08-04 jrmu (define (first-exp seq) (car seq))
267 665c255d 2023-08-04 jrmu (define (rest-exps seq) (cdr seq))
268 665c255d 2023-08-04 jrmu (define (sequence->exp seq)
269 665c255d 2023-08-04 jrmu (cond ((null? seq) seq)
270 665c255d 2023-08-04 jrmu ((last-exp? seq) (first-exp seq))
271 665c255d 2023-08-04 jrmu (else (make-begin seq))))
272 665c255d 2023-08-04 jrmu (define (make-begin seq) (cons 'begin seq))
273 665c255d 2023-08-04 jrmu (define (eval-sequence exps env)
274 665c255d 2023-08-04 jrmu (cond ((last-exp? exps) (eval (first-exp exps) env))
275 665c255d 2023-08-04 jrmu (else (eval (first-exp exps) env)
276 665c255d 2023-08-04 jrmu (eval-sequence (rest-exps exps) env))))
278 665c255d 2023-08-04 jrmu ;; application
279 665c255d 2023-08-04 jrmu (define (application? exp) (pair? exp))
280 665c255d 2023-08-04 jrmu (define (operator exp) (car exp))
281 665c255d 2023-08-04 jrmu (define (operands exp) (cdr exp))
282 665c255d 2023-08-04 jrmu (define (no-operands? ops) (null? ops))
283 665c255d 2023-08-04 jrmu (define (first-operand ops) (car ops))
284 665c255d 2023-08-04 jrmu (define (rest-operands ops) (cdr ops))
287 665c255d 2023-08-04 jrmu (define (cond? exp) (tagged-list? exp 'cond))
288 665c255d 2023-08-04 jrmu (define (cond-clauses exp) (cdr exp))
289 665c255d 2023-08-04 jrmu (define (cond-else-clause? clause)
290 665c255d 2023-08-04 jrmu (eq? (cond-predicate clause) 'else))
291 665c255d 2023-08-04 jrmu (define (cond-predicate clause) (car clause))
292 665c255d 2023-08-04 jrmu (define (cond-actions clause) (cdr clause))
293 665c255d 2023-08-04 jrmu (define (cond-extended-clause? clause)
294 665c255d 2023-08-04 jrmu (and (not (null? (cdr clause))) (eq? (cadr clause) '=>)))
295 665c255d 2023-08-04 jrmu (define (cond-extended-proc clause)
296 665c255d 2023-08-04 jrmu (caddr clause))
297 665c255d 2023-08-04 jrmu (define (cond->if exp)
298 665c255d 2023-08-04 jrmu (expand-clauses (cond-clauses exp)))
299 665c255d 2023-08-04 jrmu (define (expand-clauses clauses)
300 665c255d 2023-08-04 jrmu (if (null? clauses)
301 665c255d 2023-08-04 jrmu 'false ; no else clause
302 665c255d 2023-08-04 jrmu (let ((first (car clauses))
303 665c255d 2023-08-04 jrmu (rest (cdr clauses)))
304 665c255d 2023-08-04 jrmu (if (cond-else-clause? first)
305 665c255d 2023-08-04 jrmu (if (null? rest)
306 665c255d 2023-08-04 jrmu (sequence->exp (cond-actions first))
307 665c255d 2023-08-04 jrmu (error "ELSE clause isn't last -- COND->IF"
309 665c255d 2023-08-04 jrmu (if (cond-extended-clause? first)
310 665c255d 2023-08-04 jrmu (make-if (cond-predicate first)
311 665c255d 2023-08-04 jrmu (make-application
312 665c255d 2023-08-04 jrmu (cond-extended-proc first)
313 665c255d 2023-08-04 jrmu (list (cond-predicate first)))
314 665c255d 2023-08-04 jrmu (expand-clauses rest))
315 665c255d 2023-08-04 jrmu (make-if (cond-predicate first)
316 665c255d 2023-08-04 jrmu (sequence->exp (cond-actions first))
317 665c255d 2023-08-04 jrmu (expand-clauses rest)))))))
318 665c255d 2023-08-04 jrmu (define (true? x)
319 665c255d 2023-08-04 jrmu (not (eq? x false)))
320 665c255d 2023-08-04 jrmu (define (false? x)
321 665c255d 2023-08-04 jrmu (eq? x false))
323 665c255d 2023-08-04 jrmu ;; procedure
324 665c255d 2023-08-04 jrmu (define (make-procedure parameters body env)
325 665c255d 2023-08-04 jrmu (list 'procedure parameters body env))
326 665c255d 2023-08-04 jrmu (define (compound-procedure? p)
327 665c255d 2023-08-04 jrmu (tagged-list? p 'procedure))
328 665c255d 2023-08-04 jrmu (define (procedure-parameters p) (cadr p))
329 665c255d 2023-08-04 jrmu (define (procedure-body p) (caddr p))
330 665c255d 2023-08-04 jrmu (define (procedure-environment p) (cadddr p))
332 665c255d 2023-08-04 jrmu ;; environment
333 665c255d 2023-08-04 jrmu (define (enclosing-environment env) (cdr env))
334 665c255d 2023-08-04 jrmu (define (first-frame env) (car env))
335 665c255d 2023-08-04 jrmu (define the-empty-environment '())
336 665c255d 2023-08-04 jrmu (define (make-frame variables values)
337 665c255d 2023-08-04 jrmu (cons variables values))
338 665c255d 2023-08-04 jrmu (define (frame-variables frame) (car frame))
339 665c255d 2023-08-04 jrmu (define (frame-values frame) (cdr frame))
340 665c255d 2023-08-04 jrmu (define (add-binding-to-frame! var val frame)
341 665c255d 2023-08-04 jrmu (set-car! frame (cons var (car frame)))
342 665c255d 2023-08-04 jrmu (set-cdr! frame (cons val (cdr frame))))
343 665c255d 2023-08-04 jrmu (define (extend-environment vars vals base-env)
344 665c255d 2023-08-04 jrmu (if (= (length vars) (length vals))
345 665c255d 2023-08-04 jrmu (cons (make-frame vars vals) base-env)
346 665c255d 2023-08-04 jrmu (if (< (length vars) (length vals))
347 665c255d 2023-08-04 jrmu (error "Too many arguments supplied" vars vals)
348 665c255d 2023-08-04 jrmu (error "Too few arguments supplied" vars vals))))
349 665c255d 2023-08-04 jrmu (define (lookup-variable-value var env)
350 665c255d 2023-08-04 jrmu (define (env-loop env)
351 665c255d 2023-08-04 jrmu (define (scan vars vals)
352 665c255d 2023-08-04 jrmu (cond ((null? vars)
353 665c255d 2023-08-04 jrmu (env-loop (enclosing-environment env)))
354 665c255d 2023-08-04 jrmu ((eq? var (car vars))
355 665c255d 2023-08-04 jrmu (car vals))
356 665c255d 2023-08-04 jrmu (else (scan (cdr vars) (cdr vals)))))
357 665c255d 2023-08-04 jrmu (if (eq? env the-empty-environment)
358 665c255d 2023-08-04 jrmu (error "Unbound variable" var)
359 665c255d 2023-08-04 jrmu (let ((frame (first-frame env)))
360 665c255d 2023-08-04 jrmu (scan (frame-variables frame)
361 665c255d 2023-08-04 jrmu (frame-values frame)))))
362 665c255d 2023-08-04 jrmu (env-loop env))
363 665c255d 2023-08-04 jrmu (define (set-variable-value! var val env)
364 665c255d 2023-08-04 jrmu (define (env-loop env)
365 665c255d 2023-08-04 jrmu (define (scan vars vals)
366 665c255d 2023-08-04 jrmu (cond ((null? vars)
367 665c255d 2023-08-04 jrmu (env-loop (enclosing-environment env)))
368 665c255d 2023-08-04 jrmu ((eq? var (car vars))
369 665c255d 2023-08-04 jrmu (set-car! vals val))
370 665c255d 2023-08-04 jrmu (else (scan (cdr vars) (cdr vals)))))
371 665c255d 2023-08-04 jrmu (if (eq? env the-empty-environment)
372 665c255d 2023-08-04 jrmu (error "Unbound variable -- SET!" var)
373 665c255d 2023-08-04 jrmu (let ((frame (first-frame env)))
374 665c255d 2023-08-04 jrmu (scan (frame-variables frame)
375 665c255d 2023-08-04 jrmu (frame-values frame)))))
376 665c255d 2023-08-04 jrmu (env-loop env))
377 665c255d 2023-08-04 jrmu (define (define-variable! var val env)
378 665c255d 2023-08-04 jrmu (let ((frame (first-frame env)))
379 665c255d 2023-08-04 jrmu (define (scan vars vals)
380 665c255d 2023-08-04 jrmu (cond ((null? vars)
381 665c255d 2023-08-04 jrmu (add-binding-to-frame! var val frame))
382 665c255d 2023-08-04 jrmu ((eq? var (car vars))
383 665c255d 2023-08-04 jrmu (set-car! vals val))
384 665c255d 2023-08-04 jrmu (else (scan (cdr vars) (cdr vals)))))
385 665c255d 2023-08-04 jrmu (scan (frame-variables frame)
386 665c255d 2023-08-04 jrmu (frame-values frame))))
388 665c255d 2023-08-04 jrmu ;; primitives
389 665c255d 2023-08-04 jrmu (define (primitive-procedure? proc)
390 665c255d 2023-08-04 jrmu (tagged-list? proc 'primitive))
391 665c255d 2023-08-04 jrmu (define (primitive-implementation proc) (cadr proc))
392 665c255d 2023-08-04 jrmu (define primitive-procedures
393 665c255d 2023-08-04 jrmu (list (list 'car car)
394 665c255d 2023-08-04 jrmu (list 'cdr cdr)
395 665c255d 2023-08-04 jrmu (list 'caar caar)
396 665c255d 2023-08-04 jrmu (list 'cadr cadr)
397 665c255d 2023-08-04 jrmu (list 'cddr cddr)
398 665c255d 2023-08-04 jrmu (list 'cons cons)
399 665c255d 2023-08-04 jrmu (list 'null? null?)
400 665c255d 2023-08-04 jrmu (list '* *)
401 665c255d 2023-08-04 jrmu (list '/ /)
402 665c255d 2023-08-04 jrmu (list '+ +)
403 665c255d 2023-08-04 jrmu (list '- -)
404 665c255d 2023-08-04 jrmu (list '= =)
405 665c255d 2023-08-04 jrmu (list '< <)
406 665c255d 2023-08-04 jrmu (list '> >)
407 665c255d 2023-08-04 jrmu (list '<= <=)
408 665c255d 2023-08-04 jrmu (list '>= >=)
409 665c255d 2023-08-04 jrmu (list 'remainder remainder)
410 665c255d 2023-08-04 jrmu (list 'eq? eq?)
411 665c255d 2023-08-04 jrmu (list 'equal? equal?)
412 665c255d 2023-08-04 jrmu (list 'display display)))
413 665c255d 2023-08-04 jrmu (define (primitive-procedure-names)
415 665c255d 2023-08-04 jrmu primitive-procedures))
416 665c255d 2023-08-04 jrmu (define (primitive-procedure-objects)
417 665c255d 2023-08-04 jrmu (map (lambda (proc) (list 'primitive (cadr proc)))
418 665c255d 2023-08-04 jrmu primitive-procedures))
419 665c255d 2023-08-04 jrmu (define (apply-primitive-procedure proc args)
420 665c255d 2023-08-04 jrmu (apply-in-underlying-scheme
421 665c255d 2023-08-04 jrmu (primitive-implementation proc) args))
423 665c255d 2023-08-04 jrmu ;; driver-loop
424 665c255d 2023-08-04 jrmu (define input-prompt ";;; M-Eval input:")
425 665c255d 2023-08-04 jrmu (define output-prompt ";;; M-Eval value:")
426 665c255d 2023-08-04 jrmu (define (driver-loop)
427 665c255d 2023-08-04 jrmu (prompt-for-input input-prompt)
428 665c255d 2023-08-04 jrmu (let ((input (read)))
429 665c255d 2023-08-04 jrmu (let ((output (eval input the-global-environment)))
430 665c255d 2023-08-04 jrmu (announce-output output-prompt)
431 665c255d 2023-08-04 jrmu (user-print output)))
432 665c255d 2023-08-04 jrmu (driver-loop))
433 665c255d 2023-08-04 jrmu (define (prompt-for-input string)
434 665c255d 2023-08-04 jrmu (newline) (newline) (display string) (newline))
436 665c255d 2023-08-04 jrmu (define (announce-output string)
437 665c255d 2023-08-04 jrmu (newline) (display string) (newline))
438 665c255d 2023-08-04 jrmu (define (user-print object)
439 665c255d 2023-08-04 jrmu (if (compound-procedure? object)
440 665c255d 2023-08-04 jrmu (display (list 'compound-procedure
441 665c255d 2023-08-04 jrmu (procedure-parameters object)
442 665c255d 2023-08-04 jrmu (procedure-body object)
443 665c255d 2023-08-04 jrmu '<procedure-env>))
444 665c255d 2023-08-04 jrmu (display object)))
445 665c255d 2023-08-04 jrmu (define (setup-environment)
446 665c255d 2023-08-04 jrmu (let ((initial-env
447 665c255d 2023-08-04 jrmu (extend-environment (primitive-procedure-names)
448 665c255d 2023-08-04 jrmu (primitive-procedure-objects)
449 665c255d 2023-08-04 jrmu the-empty-environment)))
450 665c255d 2023-08-04 jrmu (define-variable! 'true true initial-env)
451 665c255d 2023-08-04 jrmu (define-variable! 'false false initial-env)
452 665c255d 2023-08-04 jrmu initial-env))
453 665c255d 2023-08-04 jrmu (define the-global-environment (setup-environment))
455 665c255d 2023-08-04 jrmu ;; auxiliary
456 665c255d 2023-08-04 jrmu (define (test-case actual expected)
458 665c255d 2023-08-04 jrmu (display "Actual: ")
459 665c255d 2023-08-04 jrmu (display actual)
461 665c255d 2023-08-04 jrmu (display "Expected: ")
462 665c255d 2023-08-04 jrmu (display expected)
464 665c255d 2023-08-04 jrmu (define (geval exp) ;; eval globally
465 665c255d 2023-08-04 jrmu (eval exp the-global-environment))
466 665c255d 2023-08-04 jrmu (define (test-eval exp expected)
467 665c255d 2023-08-04 jrmu (test-case (geval exp) expected))
469 665c255d 2023-08-04 jrmu ;; Exercise 4.15. Given a one-argument procedure p and an object a, p is said to ``halt'' on a if evaluating the expression (p a) returns a value (as opposed to terminating with an error message or running forever). Show that it is impossible to write a procedure halts? that correctly determines whether p halts on a for any procedure p and object a. Use the following reasoning: If you had such a procedure halts?, you could implement the following program:
471 665c255d 2023-08-04 jrmu (define (run-forever) (run-forever))
473 665c255d 2023-08-04 jrmu (define (try p)
474 665c255d 2023-08-04 jrmu (if (halts? p p)
475 665c255d 2023-08-04 jrmu (run-forever)
478 665c255d 2023-08-04 jrmu ;; Now consider evaluating the expression (try try) and show that any possible outcome (either halting or running forever) violates the intended behavior of halts?.23
480 665c255d 2023-08-04 jrmu If (try try)
482 665c255d 2023-08-04 jrmu ;; test-suite
484 665c255d 2023-08-04 jrmu ;; procedure definitions
487 665c255d 2023-08-04 jrmu '(define (assoc key records)
488 665c255d 2023-08-04 jrmu (cond ((null? records) false)
489 665c255d 2023-08-04 jrmu ((equal? key (caar records)) (car records))
490 665c255d 2023-08-04 jrmu (else (assoc key (cdr records))))))
493 665c255d 2023-08-04 jrmu '(define (map proc list)
494 665c255d 2023-08-04 jrmu (if (null? list)
496 665c255d 2023-08-04 jrmu (cons (proc (car list))
497 665c255d 2023-08-04 jrmu (map proc (cdr list))))))
500 665c255d 2023-08-04 jrmu '(define (accumulate op initial sequence)
501 665c255d 2023-08-04 jrmu (if (null? sequence)
503 665c255d 2023-08-04 jrmu (op (car sequence)
504 665c255d 2023-08-04 jrmu (accumulate op initial (cdr sequence))))))
506 665c255d 2023-08-04 jrmu ;; all special forms
507 665c255d 2023-08-04 jrmu (test-eval '(begin 5 6) 6)
508 665c255d 2023-08-04 jrmu (test-eval '10 10)
509 665c255d 2023-08-04 jrmu (geval '(define x 3))
510 665c255d 2023-08-04 jrmu (test-eval 'x 3)
511 665c255d 2023-08-04 jrmu (test-eval '(set! x -25) 'ok)
512 665c255d 2023-08-04 jrmu (test-eval 'x -25)
513 665c255d 2023-08-04 jrmu (geval '(define z (lambda (x y) (+ x (* x y)))))
514 665c255d 2023-08-04 jrmu (test-eval '(z 3 4) 15)
515 665c255d 2023-08-04 jrmu (test-eval '(cond ((= x -2) 'x=-2)
516 665c255d 2023-08-04 jrmu ((= x -25) 'x=-25)
517 665c255d 2023-08-04 jrmu (else 'failed))
519 665c255d 2023-08-04 jrmu (test-eval '(if true false true) false)
521 665c255d 2023-08-04 jrmu '(let ((x 4) (y 7))
522 665c255d 2023-08-04 jrmu (+ x y (* x y)))
523 665c255d 2023-08-04 jrmu (+ 4 7 (* 4 7)))
527 665c255d 2023-08-04 jrmu (geval '(define x (+ 3 8)))
528 665c255d 2023-08-04 jrmu (test-eval '(and 0 true x) 11)
529 665c255d 2023-08-04 jrmu (test-eval '(and 0 true x false) false)
530 665c255d 2023-08-04 jrmu (test-eval '(and 0 true x (set! x -2) false) false)
531 665c255d 2023-08-04 jrmu (test-eval 'x -2)
532 665c255d 2023-08-04 jrmu (test-eval '(and 0 true x false (set! x -5)) false)
533 665c255d 2023-08-04 jrmu (test-eval 'x -2)
534 665c255d 2023-08-04 jrmu (test-eval '(or false (set! x 25)) 'ok)
535 665c255d 2023-08-04 jrmu (test-eval 'x 25)
536 665c255d 2023-08-04 jrmu (test-eval '(or (set! x 2) (set! x 4)) 'ok)
537 665c255d 2023-08-04 jrmu (test-eval 'x 2)
538 665c255d 2023-08-04 jrmu (test-eval '(or false (set! x 25) true false) 'ok)
539 665c255d 2023-08-04 jrmu (test-eval 'x 25)
540 665c255d 2023-08-04 jrmu (test-eval '(or ((lambda (x) x) 5)) 5)
541 665c255d 2023-08-04 jrmu (test-eval '(or (begin (set! x (+ x 1)) x)) 26)
547 665c255d 2023-08-04 jrmu '(cond ((assoc 'b '((a 1) (b 2))) => cadr)
548 665c255d 2023-08-04 jrmu (else false))
552 665c255d 2023-08-04 jrmu '(cond ((= 3 4) 'not-true)
553 665c255d 2023-08-04 jrmu ((= (* 2 4) 3) 'also-false)
554 665c255d 2023-08-04 jrmu ((map (lambda (x)
555 665c255d 2023-08-04 jrmu (* x (+ x 1)))
556 665c255d 2023-08-04 jrmu '(2 4 1 9))
558 665c255d 2023-08-04 jrmu (lambda (x)
559 665c255d 2023-08-04 jrmu (accumulate + 0 x)))
560 665c255d 2023-08-04 jrmu (else 'never-reach))
562 665c255d 2023-08-04 jrmu ;; '(6 20 2 90)
565 665c255d 2023-08-04 jrmu ;; procedure definition and application
567 665c255d 2023-08-04 jrmu '(define (factorial n)
568 665c255d 2023-08-04 jrmu (if (= n 0)
570 665c255d 2023-08-04 jrmu (* n (factorial (- n 1))))))
571 665c255d 2023-08-04 jrmu (test-eval '(factorial 5) 120)
576 665c255d 2023-08-04 jrmu '(map (lambda (x)
577 665c255d 2023-08-04 jrmu (* x (+ x 1)))
578 665c255d 2023-08-04 jrmu '(2 1 4 2 8 3))
579 665c255d 2023-08-04 jrmu '(6 2 20 6 72 12))
580 665c255d 2023-08-04 jrmu ;; accumulate
583 665c255d 2023-08-04 jrmu '(accumulate + 0 '(1 2 3 4 5))
586 665c255d 2023-08-04 jrmu ;; make-let
588 665c255d 2023-08-04 jrmu (make-let '(x y) '(3 5) '((+ x y)))
595 665c255d 2023-08-04 jrmu '(let ((x 3))
599 665c255d 2023-08-04 jrmu '(let ((x 3)
604 665c255d 2023-08-04 jrmu '(let ((x 3)
606 665c255d 2023-08-04 jrmu (+ (let ((x (+ y 2))
610 665c255d 2023-08-04 jrmu (+ (* 4 3) 3 2))
612 665c255d 2023-08-04 jrmu '(let ((x 6)
613 665c255d 2023-08-04 jrmu (y (let ((x 2))
615 665c255d 2023-08-04 jrmu (z (let ((a (* 3 2)))
624 665c255d 2023-08-04 jrmu '(let* ((x 3)
625 665c255d 2023-08-04 jrmu (y (+ x 2))
626 665c255d 2023-08-04 jrmu (z (+ x y 5)))
635 665c255d 2023-08-04 jrmu '(let* ((x 3))
636 665c255d 2023-08-04 jrmu (let* ((y 5))
641 665c255d 2023-08-04 jrmu '(let* ((x 3)
642 665c255d 2023-08-04 jrmu (y (+ x 1)))
643 665c255d 2023-08-04 jrmu (+ (let* ((x (+ y 2))
647 665c255d 2023-08-04 jrmu (+ (* 6 6) 3 4))
649 665c255d 2023-08-04 jrmu '(let* ((x 6)
650 665c255d 2023-08-04 jrmu (y (let* ((x 2)
651 665c255d 2023-08-04 jrmu (a (let* ((x (* 3 x)))
654 665c255d 2023-08-04 jrmu (z (+ x y)))
658 665c255d 2023-08-04 jrmu ;; named-let
661 665c255d 2023-08-04 jrmu '(let eight ()
667 665c255d 2023-08-04 jrmu '(let loop ((count 0))
668 665c255d 2023-08-04 jrmu (if (= 100 count)
670 665c255d 2023-08-04 jrmu (loop (+ count 1))))
673 665c255d 2023-08-04 jrmu '(define (prime? x)
674 665c255d 2023-08-04 jrmu (let prime-iter ((i 2))
675 665c255d 2023-08-04 jrmu (cond ((> (* i i) x) true)
676 665c255d 2023-08-04 jrmu ((= (remainder x i) 0) false)
677 665c255d 2023-08-04 jrmu (else (prime-iter (+ i 1)))))))
679 665c255d 2023-08-04 jrmu '(let primes ((x 2)
681 665c255d 2023-08-04 jrmu (cond ((= n 0) '())
682 665c255d 2023-08-04 jrmu ((prime? x)
684 665c255d 2023-08-04 jrmu (primes (+ x 1) (- n 1))))
685 665c255d 2023-08-04 jrmu (else (primes (+ x 1) n))))
686 665c255d 2023-08-04 jrmu '(2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71))
689 665c255d 2023-08-04 jrmu '(define (fib n)
690 665c255d 2023-08-04 jrmu (let fib-iter ((a 1)
693 665c255d 2023-08-04 jrmu (if (= count 0)
695 665c255d 2023-08-04 jrmu (fib-iter (+ a b) a (- count 1))))))
696 665c255d 2023-08-04 jrmu (test-eval '(fib 19) 4181)
700 665c255d 2023-08-04 jrmu '(let ((y 0))
701 665c255d 2023-08-04 jrmu (do ((x 0 (+ x 1)))
702 665c255d 2023-08-04 jrmu ((= x 5) y)
703 665c255d 2023-08-04 jrmu (set! y (+ y 1))))
714 665c255d 2023-08-04 jrmu '(let ((y 0))
716 665c255d 2023-08-04 jrmu ((= y 5) y)
717 665c255d 2023-08-04 jrmu (set! y (+ y 1))))
721 665c255d 2023-08-04 jrmu '(do ((y '(1 2 3 4)))
722 665c255d 2023-08-04 jrmu ((null? y))
723 665c255d 2023-08-04 jrmu (set! y (cdr y)))
726 665c255d 2023-08-04 jrmu '(let ((y 0))
727 665c255d 2023-08-04 jrmu (do ((x 0 (+ x 1)))
728 665c255d 2023-08-04 jrmu ((= x 5) y)
729 665c255d 2023-08-04 jrmu (set! y (+ y 1))))
732 665c255d 2023-08-04 jrmu '(let ((x '(1 3 5 7 9)))
733 665c255d 2023-08-04 jrmu (do ((x x (cdr x))
734 665c255d 2023-08-04 jrmu (sum 0 (+ sum (car x))))
735 665c255d 2023-08-04 jrmu ((null? x) sum)))
738 665c255d 2023-08-04 jrmu '(let ((z '()))
739 665c255d 2023-08-04 jrmu (do ((x '(1 2 3 4) (cdr x))
740 665c255d 2023-08-04 jrmu (y '(1 2 3 4 5 6 7 8) (cddr y)))
741 665c255d 2023-08-04 jrmu ((null? x) y x z)
742 665c255d 2023-08-04 jrmu (set! z (cons (car x) z))))
743 665c255d 2023-08-04 jrmu '(4 3 2 1))
745 665c255d 2023-08-04 jrmu ;; make-unbound!
748 665c255d 2023-08-04 jrmu '(let ((x 3))
749 665c255d 2023-08-04 jrmu (let ((x 5))
750 665c255d 2023-08-04 jrmu (make-unbound! x)
755 665c255d 2023-08-04 jrmu '(let ((x 3))
756 665c255d 2023-08-04 jrmu (let ((x 5))
757 665c255d 2023-08-04 jrmu (define y x)
758 665c255d 2023-08-04 jrmu (make-unbound! x)
763 665c255d 2023-08-04 jrmu '(let ((y -1) (x 3))
764 665c255d 2023-08-04 jrmu (let ((y 0.5) (x 5))
765 665c255d 2023-08-04 jrmu (define a x)
766 665c255d 2023-08-04 jrmu (define b y)
767 665c255d 2023-08-04 jrmu (make-unbound! x)
768 665c255d 2023-08-04 jrmu (make-unbound! y)
769 665c255d 2023-08-04 jrmu (* a b x y)))
770 665c255d 2023-08-04 jrmu (* 5 3 -1 0.5))
773 665c255d 2023-08-04 jrmu '(let ((x 3) (y 4))
774 665c255d 2023-08-04 jrmu (let ((x 5))
775 665c255d 2023-08-04 jrmu (make-unbound! x)
780 665c255d 2023-08-04 jrmu '(let ((a 1) (b 2) (c 3) (d 4))
781 665c255d 2023-08-04 jrmu (make-unbound! b)
786 665c255d 2023-08-04 jrmu '(let ((x 4) (y 5))
787 665c255d 2023-08-04 jrmu (let ((a 1) (b 2) (c 3))
788 665c255d 2023-08-04 jrmu (let ((x (+ a b)) (y (+ c a)))
789 665c255d 2023-08-04 jrmu (make-unbound! x)
790 665c255d 2023-08-04 jrmu (let ((a x) (b (+ x y)))
791 665c255d 2023-08-04 jrmu (define z b)
792 665c255d 2023-08-04 jrmu (make-unbound! b)
794 665c255d 2023-08-04 jrmu (+ a b y))))))
796 665c255d 2023-08-04 jrmu (+ 4 2 4)))
