1 665c255d 2023-08-04 jrmu (define (eval exp env)
2 665c255d 2023-08-04 jrmu (cond ((self-evaluating? exp) exp)
3 665c255d 2023-08-04 jrmu ((variable? exp) (lookup-variable-value exp env))
4 665c255d 2023-08-04 jrmu ((quoted? exp) (text-of-quotation exp))
5 665c255d 2023-08-04 jrmu ((assignment? exp) (eval-assignment exp env))
6 665c255d 2023-08-04 jrmu ((definition? exp) (eval-definition exp env))
7 665c255d 2023-08-04 jrmu ((if? exp) (eval-if exp env))
8 665c255d 2023-08-04 jrmu ((and? exp) (eval-and exp env))
9 665c255d 2023-08-04 jrmu ((or? exp) (eval-or exp env))
10 665c255d 2023-08-04 jrmu ((lambda? exp)
11 665c255d 2023-08-04 jrmu (make-procedure (lambda-parameters exp)
12 665c255d 2023-08-04 jrmu (lambda-body exp)
14 665c255d 2023-08-04 jrmu ((begin? exp)
15 665c255d 2023-08-04 jrmu (eval-sequence (begin-actions exp) env))
16 665c255d 2023-08-04 jrmu ((cond? exp) (eval (cond->if exp) env))
17 665c255d 2023-08-04 jrmu ((let? exp) (eval (let->combination exp) env))
18 665c255d 2023-08-04 jrmu ((let*? exp) (eval (let*->nested-lets exp) env))
19 665c255d 2023-08-04 jrmu ((named-let? exp) (eval (named-let->combination exp) env))
20 665c255d 2023-08-04 jrmu ((do? exp) (eval (do->combination exp) env))
21 665c255d 2023-08-04 jrmu ((application? exp)
22 665c255d 2023-08-04 jrmu (apply (eval (operator exp) env)
23 665c255d 2023-08-04 jrmu (list-of-values (operands exp) env)))
25 665c255d 2023-08-04 jrmu (error "Unknown expression type -- EVAL" exp))))
26 665c255d 2023-08-04 jrmu (define (apply procedure arguments)
27 665c255d 2023-08-04 jrmu (cond ((primitive-procedure? procedure)
28 665c255d 2023-08-04 jrmu (apply-primitive-procedure procedure arguments))
29 665c255d 2023-08-04 jrmu ((compound-procedure? procedure)
30 665c255d 2023-08-04 jrmu (eval-sequence
31 665c255d 2023-08-04 jrmu (procedure-body procedure)
32 665c255d 2023-08-04 jrmu (extend-environment
33 665c255d 2023-08-04 jrmu (procedure-parameters procedure)
35 665c255d 2023-08-04 jrmu (procedure-environment procedure))))
38 665c255d 2023-08-04 jrmu "Unknown procedure type -- APPLY" procedure))))
40 665c255d 2023-08-04 jrmu (define (list-of-values exps env)
41 665c255d 2023-08-04 jrmu (if (no-operands? exps)
43 665c255d 2023-08-04 jrmu (cons (eval (first-operand exps) env)
44 665c255d 2023-08-04 jrmu (list-of-values (rest-operands exps) env))))
46 665c255d 2023-08-04 jrmu (define (tagged-list? exp tag)
47 665c255d 2023-08-04 jrmu (if (pair? exp)
48 665c255d 2023-08-04 jrmu (eq? (car exp) tag)
51 665c255d 2023-08-04 jrmu ;; self-evaluating/variable/quoted
52 665c255d 2023-08-04 jrmu (define (self-evaluating? exp)
53 665c255d 2023-08-04 jrmu (cond ((number? exp) true)
54 665c255d 2023-08-04 jrmu ((string? exp) true)
55 665c255d 2023-08-04 jrmu (else false)))
56 665c255d 2023-08-04 jrmu (define (variable? exp) (symbol? exp))
57 665c255d 2023-08-04 jrmu (define (quoted? exp)
58 665c255d 2023-08-04 jrmu (tagged-list? exp 'quote))
59 665c255d 2023-08-04 jrmu (define (text-of-quotation exp) (cadr exp))
61 665c255d 2023-08-04 jrmu ;; assignment/definition
62 665c255d 2023-08-04 jrmu (define (assignment? exp)
63 665c255d 2023-08-04 jrmu (tagged-list? exp 'set!))
64 665c255d 2023-08-04 jrmu (define (assignment-variable exp) (cadr exp))
65 665c255d 2023-08-04 jrmu (define (assignment-value exp) (caddr exp))
66 665c255d 2023-08-04 jrmu (define (definition? exp)
67 665c255d 2023-08-04 jrmu (tagged-list? exp 'define))
68 665c255d 2023-08-04 jrmu (define (definition-variable exp)
69 665c255d 2023-08-04 jrmu (if (symbol? (cadr exp))
71 665c255d 2023-08-04 jrmu (caadr exp)))
72 665c255d 2023-08-04 jrmu (define (definition-value exp)
73 665c255d 2023-08-04 jrmu (if (symbol? (cadr exp))
75 665c255d 2023-08-04 jrmu (make-lambda (cdadr exp) ; formal parameters
76 665c255d 2023-08-04 jrmu (cddr exp)))) ; body
77 665c255d 2023-08-04 jrmu (define (eval-assignment exp env)
78 665c255d 2023-08-04 jrmu (set-variable-value! (assignment-variable exp)
79 665c255d 2023-08-04 jrmu (eval (assignment-value exp) env)
82 665c255d 2023-08-04 jrmu (define (eval-definition exp env)
83 665c255d 2023-08-04 jrmu (define-variable! (definition-variable exp)
84 665c255d 2023-08-04 jrmu (eval (definition-value exp) env)
87 665c255d 2023-08-04 jrmu (define (make-definition var val)
88 665c255d 2023-08-04 jrmu `(define ,var ,val))
91 665c255d 2023-08-04 jrmu ;; if/and/or
92 665c255d 2023-08-04 jrmu (define (if? exp) (tagged-list? exp 'if))
93 665c255d 2023-08-04 jrmu (define (if-predicate exp) (cadr exp))
94 665c255d 2023-08-04 jrmu (define (if-consequent exp) (caddr exp))
95 665c255d 2023-08-04 jrmu (define (if-alternative exp)
96 665c255d 2023-08-04 jrmu (if (not (null? (cdddr exp)))
97 665c255d 2023-08-04 jrmu (cadddr exp)
99 665c255d 2023-08-04 jrmu (define (make-if predicate consequent alternative)
100 665c255d 2023-08-04 jrmu (list 'if predicate consequent alternative))
101 665c255d 2023-08-04 jrmu (define (eval-if exp env)
102 665c255d 2023-08-04 jrmu (if (true? (eval (if-predicate exp) env))
103 665c255d 2023-08-04 jrmu (eval (if-consequent exp) env)
104 665c255d 2023-08-04 jrmu (eval (if-alternative exp) env)))
106 665c255d 2023-08-04 jrmu (define (and? exp)
107 665c255d 2023-08-04 jrmu (tagged-list? exp 'and))
108 665c255d 2023-08-04 jrmu (define (and-clauses exp)
110 665c255d 2023-08-04 jrmu (define (or? exp)
111 665c255d 2023-08-04 jrmu (tagged-list? exp 'or))
112 665c255d 2023-08-04 jrmu (define (or-clauses exp)
114 665c255d 2023-08-04 jrmu (define (eval-and exp env)
115 665c255d 2023-08-04 jrmu (define (eval-clauses clauses)
116 665c255d 2023-08-04 jrmu (cond ((null? clauses) true)
117 665c255d 2023-08-04 jrmu ((null? (cdr clauses)) (eval (car clauses) env))
118 665c255d 2023-08-04 jrmu (else (and (eval (car clauses) env)
119 665c255d 2023-08-04 jrmu (eval-clauses (cdr clauses))))))
120 665c255d 2023-08-04 jrmu (eval-clauses (and-clauses exp)))
121 665c255d 2023-08-04 jrmu (define (eval-or exp env)
122 665c255d 2023-08-04 jrmu (define (eval-clauses clauses)
123 665c255d 2023-08-04 jrmu (if (null? clauses)
125 665c255d 2023-08-04 jrmu (or (eval (car clauses) env)
126 665c255d 2023-08-04 jrmu (eval-clauses (cdr clauses)))))
127 665c255d 2023-08-04 jrmu (eval-clauses (or-clauses exp)))
130 665c255d 2023-08-04 jrmu ;; lambda/let/let*
131 665c255d 2023-08-04 jrmu (define (lambda? exp) (tagged-list? exp 'lambda))
132 665c255d 2023-08-04 jrmu (define (lambda-parameters exp) (cadr exp))
133 665c255d 2023-08-04 jrmu (define (lambda-body exp) (cddr exp))
134 665c255d 2023-08-04 jrmu (define (make-lambda parameters body)
135 665c255d 2023-08-04 jrmu (cons 'lambda (cons parameters body)))
137 665c255d 2023-08-04 jrmu (define (make-let vars vals body)
139 665c255d 2023-08-04 jrmu (cons (map list vars vals)
141 665c255d 2023-08-04 jrmu (define (let? exp)
142 665c255d 2023-08-04 jrmu (and (tagged-list? exp 'let)
143 665c255d 2023-08-04 jrmu (not (symbol? (cadr exp)))))
144 665c255d 2023-08-04 jrmu (define (let-vars exp)
145 665c255d 2023-08-04 jrmu (map car (cadr exp)))
146 665c255d 2023-08-04 jrmu (define (let-vals exp)
147 665c255d 2023-08-04 jrmu (map cadr (cadr exp)))
148 665c255d 2023-08-04 jrmu (define (let-body exp)
149 665c255d 2023-08-04 jrmu (cddr exp))
150 665c255d 2023-08-04 jrmu (define (let->combination exp)
151 665c255d 2023-08-04 jrmu (make-application (make-lambda (let-vars exp) (let-body exp))
152 665c255d 2023-08-04 jrmu (let-vals exp)))
153 665c255d 2023-08-04 jrmu (define (named-let? exp)
154 665c255d 2023-08-04 jrmu (and (tagged-list? exp 'let)
155 665c255d 2023-08-04 jrmu (symbol? (cadr exp))))
156 665c255d 2023-08-04 jrmu (define (named-let-name exp)
157 665c255d 2023-08-04 jrmu (cadr exp))
158 665c255d 2023-08-04 jrmu (define (named-let-vars exp)
159 665c255d 2023-08-04 jrmu (map car (caddr exp)))
160 665c255d 2023-08-04 jrmu (define (named-let-vals exp)
161 665c255d 2023-08-04 jrmu (map cadr (caddr exp)))
162 665c255d 2023-08-04 jrmu (define (named-let-body exp)
163 665c255d 2023-08-04 jrmu (cdddr exp))
164 665c255d 2023-08-04 jrmu (define (named-let->combination exp)
165 665c255d 2023-08-04 jrmu (sequence->exp
166 665c255d 2023-08-04 jrmu (list (make-definition (named-let-name exp)
167 665c255d 2023-08-04 jrmu (make-lambda (named-let-vars exp)
168 665c255d 2023-08-04 jrmu (named-let-body exp)))
169 665c255d 2023-08-04 jrmu (make-application (named-let-name exp)
170 665c255d 2023-08-04 jrmu (named-let-vals exp)))))
171 665c255d 2023-08-04 jrmu (define (make-named-let name vars vals body)
174 665c255d 2023-08-04 jrmu (cons (map list vars vals)
177 665c255d 2023-08-04 jrmu (define (make-application op args)
178 665c255d 2023-08-04 jrmu (cons op args))
180 665c255d 2023-08-04 jrmu (define (let*? exp)
181 665c255d 2023-08-04 jrmu (tagged-list? exp 'let*))
182 665c255d 2023-08-04 jrmu (define let*-vars let-vars)
183 665c255d 2023-08-04 jrmu (define let*-vals let-vals)
184 665c255d 2023-08-04 jrmu (define let*-body let-body)
185 665c255d 2023-08-04 jrmu (define (let*->nested-lets exp)
186 665c255d 2023-08-04 jrmu (define (expand-lets vars vals)
187 665c255d 2023-08-04 jrmu (if (null? (cdr vars))
188 665c255d 2023-08-04 jrmu (make-let (list (car vars))
189 665c255d 2023-08-04 jrmu (list (car vals))
190 665c255d 2023-08-04 jrmu (let*-body exp))
191 665c255d 2023-08-04 jrmu (make-let (list (car vars))
192 665c255d 2023-08-04 jrmu (list (car vals))
193 665c255d 2023-08-04 jrmu (list (expand-lets (cdr vars) (cdr vals))))))
194 665c255d 2023-08-04 jrmu (let ((vars (let*-vars exp))
195 665c255d 2023-08-04 jrmu (vals (let*-vals exp)))
196 665c255d 2023-08-04 jrmu (if (null? vars)
197 665c255d 2023-08-04 jrmu (sequence->exp (let*-body exp))
198 665c255d 2023-08-04 jrmu (expand-lets vars vals))))
201 665c255d 2023-08-04 jrmu (define (do? exp)
202 665c255d 2023-08-04 jrmu (tagged-list? exp 'do))
203 665c255d 2023-08-04 jrmu (define (do-vars exp)
204 665c255d 2023-08-04 jrmu (map car (cadr exp)))
205 665c255d 2023-08-04 jrmu (define (do-inits exp)
206 665c255d 2023-08-04 jrmu (map cadr (cadr exp)))
207 665c255d 2023-08-04 jrmu (define (do-steps exp)
208 665c255d 2023-08-04 jrmu (map (lambda (var-init-step)
209 665c255d 2023-08-04 jrmu (if (null? (cddr var-init-step))
210 665c255d 2023-08-04 jrmu (car var-init-step)
211 665c255d 2023-08-04 jrmu (caddr var-init-step)))
212 665c255d 2023-08-04 jrmu (cadr exp)))
213 665c255d 2023-08-04 jrmu (define (do-test exp)
214 665c255d 2023-08-04 jrmu (caaddr exp))
215 665c255d 2023-08-04 jrmu (define (do-expressions exp)
216 665c255d 2023-08-04 jrmu (if (null? (cdaddr exp))
217 665c255d 2023-08-04 jrmu (caddr exp)
218 665c255d 2023-08-04 jrmu (cdaddr exp)))
219 665c255d 2023-08-04 jrmu (define (do-commands exp)
220 665c255d 2023-08-04 jrmu (cdddr exp))
221 665c255d 2023-08-04 jrmu (define (do->combination exp)
222 665c255d 2023-08-04 jrmu (make-named-let
224 665c255d 2023-08-04 jrmu (do-vars exp)
225 665c255d 2023-08-04 jrmu (do-inits exp)
228 665c255d 2023-08-04 jrmu (do-test exp)
229 665c255d 2023-08-04 jrmu (sequence->exp (do-expressions exp))
230 665c255d 2023-08-04 jrmu (sequence->exp
231 665c255d 2023-08-04 jrmu (append (do-commands exp)
232 665c255d 2023-08-04 jrmu (list (make-application
234 665c255d 2023-08-04 jrmu (do-steps exp)))))))))
237 665c255d 2023-08-04 jrmu ;; begin/sequence
238 665c255d 2023-08-04 jrmu (define (begin? exp) (tagged-list? exp 'begin))
239 665c255d 2023-08-04 jrmu (define (begin-actions exp) (cdr exp))
240 665c255d 2023-08-04 jrmu (define (last-exp? seq) (null? (cdr seq)))
241 665c255d 2023-08-04 jrmu (define (first-exp seq) (car seq))
242 665c255d 2023-08-04 jrmu (define (rest-exps seq) (cdr seq))
243 665c255d 2023-08-04 jrmu (define (sequence->exp seq)
244 665c255d 2023-08-04 jrmu (cond ((null? seq) seq)
245 665c255d 2023-08-04 jrmu ((last-exp? seq) (first-exp seq))
246 665c255d 2023-08-04 jrmu (else (make-begin seq))))
247 665c255d 2023-08-04 jrmu (define (make-begin seq) (cons 'begin seq))
248 665c255d 2023-08-04 jrmu (define (eval-sequence exps env)
249 665c255d 2023-08-04 jrmu (cond ((last-exp? exps) (eval (first-exp exps) env))
250 665c255d 2023-08-04 jrmu (else (eval (first-exp exps) env)
251 665c255d 2023-08-04 jrmu (eval-sequence (rest-exps exps) env))))
253 665c255d 2023-08-04 jrmu ;; application
254 665c255d 2023-08-04 jrmu (define (application? exp) (pair? exp))
255 665c255d 2023-08-04 jrmu (define (operator exp) (car exp))
256 665c255d 2023-08-04 jrmu (define (operands exp) (cdr exp))
257 665c255d 2023-08-04 jrmu (define (no-operands? ops) (null? ops))
258 665c255d 2023-08-04 jrmu (define (first-operand ops) (car ops))
259 665c255d 2023-08-04 jrmu (define (rest-operands ops) (cdr ops))
262 665c255d 2023-08-04 jrmu (define (cond? exp) (tagged-list? exp 'cond))
263 665c255d 2023-08-04 jrmu (define (cond-clauses exp) (cdr exp))
264 665c255d 2023-08-04 jrmu (define (cond-else-clause? clause)
265 665c255d 2023-08-04 jrmu (eq? (cond-predicate clause) 'else))
266 665c255d 2023-08-04 jrmu (define (cond-predicate clause) (car clause))
267 665c255d 2023-08-04 jrmu (define (cond-actions clause) (cdr clause))
268 665c255d 2023-08-04 jrmu (define (cond-extended-clause? clause)
269 665c255d 2023-08-04 jrmu (and (not (null? (cdr clause))) (eq? (cadr clause) '=>)))
270 665c255d 2023-08-04 jrmu (define (cond-extended-proc clause)
271 665c255d 2023-08-04 jrmu (caddr clause))
272 665c255d 2023-08-04 jrmu (define (cond->if exp)
273 665c255d 2023-08-04 jrmu (expand-clauses (cond-clauses exp)))
274 665c255d 2023-08-04 jrmu (define (expand-clauses clauses)
275 665c255d 2023-08-04 jrmu (if (null? clauses)
276 665c255d 2023-08-04 jrmu 'false ; no else clause
277 665c255d 2023-08-04 jrmu (let ((first (car clauses))
278 665c255d 2023-08-04 jrmu (rest (cdr clauses)))
279 665c255d 2023-08-04 jrmu (if (cond-else-clause? first)
280 665c255d 2023-08-04 jrmu (if (null? rest)
281 665c255d 2023-08-04 jrmu (sequence->exp (cond-actions first))
282 665c255d 2023-08-04 jrmu (error "ELSE clause isn't last -- COND->IF"
284 665c255d 2023-08-04 jrmu (if (cond-extended-clause? first)
285 665c255d 2023-08-04 jrmu (make-if (cond-predicate first)
286 665c255d 2023-08-04 jrmu (make-application
287 665c255d 2023-08-04 jrmu (cond-extended-proc first)
288 665c255d 2023-08-04 jrmu (list (cond-predicate first)))
289 665c255d 2023-08-04 jrmu (expand-clauses rest))
290 665c255d 2023-08-04 jrmu (make-if (cond-predicate first)
291 665c255d 2023-08-04 jrmu (sequence->exp (cond-actions first))
292 665c255d 2023-08-04 jrmu (expand-clauses rest)))))))
293 665c255d 2023-08-04 jrmu (define (true? x)
294 665c255d 2023-08-04 jrmu (not (eq? x false)))
295 665c255d 2023-08-04 jrmu (define (false? x)
296 665c255d 2023-08-04 jrmu (eq? x false))
298 665c255d 2023-08-04 jrmu ;; procedure
299 665c255d 2023-08-04 jrmu (define (make-procedure parameters body env)
300 665c255d 2023-08-04 jrmu (list 'procedure parameters body env))
301 665c255d 2023-08-04 jrmu (define (compound-procedure? p)
302 665c255d 2023-08-04 jrmu (tagged-list? p 'procedure))
303 665c255d 2023-08-04 jrmu (define (procedure-parameters p) (cadr p))
304 665c255d 2023-08-04 jrmu (define (procedure-body p) (caddr p))
305 665c255d 2023-08-04 jrmu (define (procedure-environment p) (cadddr p))
307 665c255d 2023-08-04 jrmu ;; environment
308 665c255d 2023-08-04 jrmu (define (enclosing-environment env) (cdr env))
309 665c255d 2023-08-04 jrmu (define (first-frame env) (car env))
310 665c255d 2023-08-04 jrmu (define the-empty-environment '())
311 665c255d 2023-08-04 jrmu (define (make-frame variables values)
312 665c255d 2023-08-04 jrmu (cons variables values))
313 665c255d 2023-08-04 jrmu (define (frame-variables frame) (car frame))
314 665c255d 2023-08-04 jrmu (define (frame-values frame) (cdr frame))
315 665c255d 2023-08-04 jrmu (define (add-binding-to-frame! var val frame)
316 665c255d 2023-08-04 jrmu (set-car! frame (cons var (car frame)))
317 665c255d 2023-08-04 jrmu (set-cdr! frame (cons val (cdr frame))))
318 665c255d 2023-08-04 jrmu (define (extend-environment vars vals base-env)
319 665c255d 2023-08-04 jrmu (if (= (length vars) (length vals))
320 665c255d 2023-08-04 jrmu (cons (make-frame vars vals) base-env)
321 665c255d 2023-08-04 jrmu (if (< (length vars) (length vals))
322 665c255d 2023-08-04 jrmu (error "Too many arguments supplied" vars vals)
323 665c255d 2023-08-04 jrmu (error "Too few arguments supplied" vars vals))))
324 665c255d 2023-08-04 jrmu (define (lookup-variable-value var env)
325 665c255d 2023-08-04 jrmu (define (env-loop env)
326 665c255d 2023-08-04 jrmu (define (scan vars vals)
327 665c255d 2023-08-04 jrmu (cond ((null? vars)
328 665c255d 2023-08-04 jrmu (env-loop (enclosing-environment env)))
329 665c255d 2023-08-04 jrmu ((eq? var (car vars))
330 665c255d 2023-08-04 jrmu (car vals))
331 665c255d 2023-08-04 jrmu (else (scan (cdr vars) (cdr vals)))))
332 665c255d 2023-08-04 jrmu (if (eq? env the-empty-environment)
333 665c255d 2023-08-04 jrmu (error "Unbound variable" var)
334 665c255d 2023-08-04 jrmu (let ((frame (first-frame env)))
335 665c255d 2023-08-04 jrmu (scan (frame-variables frame)
336 665c255d 2023-08-04 jrmu (frame-values frame)))))
337 665c255d 2023-08-04 jrmu (env-loop env))
338 665c255d 2023-08-04 jrmu (define (set-variable-value! var val env)
339 665c255d 2023-08-04 jrmu (define (env-loop env)
340 665c255d 2023-08-04 jrmu (define (scan vars vals)
341 665c255d 2023-08-04 jrmu (cond ((null? vars)
342 665c255d 2023-08-04 jrmu (env-loop (enclosing-environment env)))
343 665c255d 2023-08-04 jrmu ((eq? var (car vars))
344 665c255d 2023-08-04 jrmu (set-car! vals val))
345 665c255d 2023-08-04 jrmu (else (scan (cdr vars) (cdr vals)))))
346 665c255d 2023-08-04 jrmu (if (eq? env the-empty-environment)
347 665c255d 2023-08-04 jrmu (error "Unbound variable -- SET!" var)
348 665c255d 2023-08-04 jrmu (let ((frame (first-frame env)))
349 665c255d 2023-08-04 jrmu (scan (frame-variables frame)
350 665c255d 2023-08-04 jrmu (frame-values frame)))))
351 665c255d 2023-08-04 jrmu (env-loop env))
352 665c255d 2023-08-04 jrmu (define (define-variable! var val env)
353 665c255d 2023-08-04 jrmu (let ((frame (first-frame env)))
354 665c255d 2023-08-04 jrmu (define (scan vars vals)
355 665c255d 2023-08-04 jrmu (cond ((null? vars)
356 665c255d 2023-08-04 jrmu (add-binding-to-frame! var val frame))
357 665c255d 2023-08-04 jrmu ((eq? var (car vars))
358 665c255d 2023-08-04 jrmu (set-car! vals val))
359 665c255d 2023-08-04 jrmu (else (scan (cdr vars) (cdr vals)))))
360 665c255d 2023-08-04 jrmu (scan (frame-variables frame)
361 665c255d 2023-08-04 jrmu (frame-values frame))))
363 665c255d 2023-08-04 jrmu ;; primitives
364 665c255d 2023-08-04 jrmu (define (primitive-procedure? proc)
365 665c255d 2023-08-04 jrmu (tagged-list? proc 'primitive))
366 665c255d 2023-08-04 jrmu (define (primitive-implementation proc) (cadr proc))
367 665c255d 2023-08-04 jrmu (define primitive-procedures
368 665c255d 2023-08-04 jrmu (list (list 'car car)
369 665c255d 2023-08-04 jrmu (list 'cdr cdr)
370 665c255d 2023-08-04 jrmu (list 'caar caar)
371 665c255d 2023-08-04 jrmu (list 'cadr cadr)
372 665c255d 2023-08-04 jrmu (list 'cddr cddr)
373 665c255d 2023-08-04 jrmu (list 'cons cons)
374 665c255d 2023-08-04 jrmu (list 'null? null?)
375 665c255d 2023-08-04 jrmu (list '* *)
376 665c255d 2023-08-04 jrmu (list '/ /)
377 665c255d 2023-08-04 jrmu (list '+ +)
378 665c255d 2023-08-04 jrmu (list '- -)
379 665c255d 2023-08-04 jrmu (list '= =)
380 665c255d 2023-08-04 jrmu (list '< <)
381 665c255d 2023-08-04 jrmu (list '> >)
382 665c255d 2023-08-04 jrmu (list '<= <=)
383 665c255d 2023-08-04 jrmu (list '>= >=)
384 665c255d 2023-08-04 jrmu (list 'remainder remainder)
385 665c255d 2023-08-04 jrmu (list 'eq? eq?)
386 665c255d 2023-08-04 jrmu (list 'equal? equal?)
387 665c255d 2023-08-04 jrmu (list 'display display)))
388 665c255d 2023-08-04 jrmu (define (primitive-procedure-names)
390 665c255d 2023-08-04 jrmu primitive-procedures))
391 665c255d 2023-08-04 jrmu (define (primitive-procedure-objects)
392 665c255d 2023-08-04 jrmu (map (lambda (proc) (list 'primitive (cadr proc)))
393 665c255d 2023-08-04 jrmu primitive-procedures))
394 665c255d 2023-08-04 jrmu (define (apply-primitive-procedure proc args)
395 665c255d 2023-08-04 jrmu (apply-in-underlying-scheme
396 665c255d 2023-08-04 jrmu (primitive-implementation proc) args))
398 665c255d 2023-08-04 jrmu ;; driver-loop
399 665c255d 2023-08-04 jrmu (define input-prompt ";;; M-Eval input:")
400 665c255d 2023-08-04 jrmu (define output-prompt ";;; M-Eval value:")
401 665c255d 2023-08-04 jrmu (define (driver-loop)
402 665c255d 2023-08-04 jrmu (prompt-for-input input-prompt)
403 665c255d 2023-08-04 jrmu (let ((input (read)))
404 665c255d 2023-08-04 jrmu (let ((output (eval input the-global-environment)))
405 665c255d 2023-08-04 jrmu (announce-output output-prompt)
406 665c255d 2023-08-04 jrmu (user-print output)))
407 665c255d 2023-08-04 jrmu (driver-loop))
408 665c255d 2023-08-04 jrmu (define (prompt-for-input string)
409 665c255d 2023-08-04 jrmu (newline) (newline) (display string) (newline))
411 665c255d 2023-08-04 jrmu (define (announce-output string)
412 665c255d 2023-08-04 jrmu (newline) (display string) (newline))
413 665c255d 2023-08-04 jrmu (define (user-print object)
414 665c255d 2023-08-04 jrmu (if (compound-procedure? object)
415 665c255d 2023-08-04 jrmu (display (list 'compound-procedure
416 665c255d 2023-08-04 jrmu (procedure-parameters object)
417 665c255d 2023-08-04 jrmu (procedure-body object)
418 665c255d 2023-08-04 jrmu '<procedure-env>))
419 665c255d 2023-08-04 jrmu (display object)))
420 665c255d 2023-08-04 jrmu (define (setup-environment)
421 665c255d 2023-08-04 jrmu (let ((initial-env
422 665c255d 2023-08-04 jrmu (extend-environment (primitive-procedure-names)
423 665c255d 2023-08-04 jrmu (primitive-procedure-objects)
424 665c255d 2023-08-04 jrmu the-empty-environment)))
425 665c255d 2023-08-04 jrmu (define-variable! 'true true initial-env)
426 665c255d 2023-08-04 jrmu (define-variable! 'false false initial-env)
427 665c255d 2023-08-04 jrmu initial-env))
428 665c255d 2023-08-04 jrmu (define the-global-environment (setup-environment))
430 665c255d 2023-08-04 jrmu ;; auxiliary
431 665c255d 2023-08-04 jrmu (define (test-case actual expected)
433 665c255d 2023-08-04 jrmu (display "Actual: ")
434 665c255d 2023-08-04 jrmu (display actual)
436 665c255d 2023-08-04 jrmu (display "Expected: ")
437 665c255d 2023-08-04 jrmu (display expected)
439 665c255d 2023-08-04 jrmu (define (geval exp) ;; eval globally
440 665c255d 2023-08-04 jrmu (eval exp the-global-environment))
441 665c255d 2023-08-04 jrmu (define (test-eval exp expected)
442 665c255d 2023-08-04 jrmu (test-case (geval exp) expected))
444 665c255d 2023-08-04 jrmu ;; Exercise 4.9. Many languages support a variety of iteration constructs, such as do, for, while, and until. In Scheme, iterative processes can be expressed in terms of ordinary procedure calls, so special iteration constructs provide no essential gain in computational power. On the other hand, such constructs are often convenient. Design some iteration constructs, give examples of their use, and show how to implement them as derived expressions.
446 665c255d 2023-08-04 jrmu ;; Implemented according to this spec:
447 665c255d 2023-08-04 jrmu ;; http://www.gnu.org/software/mit-scheme/documentation/mit-scheme-ref/Iteration.html
451 665c255d 2023-08-04 jrmu ;; test-suite
453 665c255d 2023-08-04 jrmu ;; procedure definitions
456 665c255d 2023-08-04 jrmu '(define (assoc key records)
457 665c255d 2023-08-04 jrmu (cond ((null? records) false)
458 665c255d 2023-08-04 jrmu ((equal? key (caar records)) (car records))
459 665c255d 2023-08-04 jrmu (else (assoc key (cdr records))))))
462 665c255d 2023-08-04 jrmu '(define (map proc list)
463 665c255d 2023-08-04 jrmu (if (null? list)
465 665c255d 2023-08-04 jrmu (cons (proc (car list))
466 665c255d 2023-08-04 jrmu (map proc (cdr list))))))
469 665c255d 2023-08-04 jrmu '(define (accumulate op initial sequence)
470 665c255d 2023-08-04 jrmu (if (null? sequence)
472 665c255d 2023-08-04 jrmu (op (car sequence)
473 665c255d 2023-08-04 jrmu (accumulate op initial (cdr sequence))))))
475 665c255d 2023-08-04 jrmu ;; all special forms
476 665c255d 2023-08-04 jrmu (test-eval '(begin 5 6) 6)
477 665c255d 2023-08-04 jrmu (test-eval '10 10)
478 665c255d 2023-08-04 jrmu (geval '(define x 3))
479 665c255d 2023-08-04 jrmu (test-eval 'x 3)
480 665c255d 2023-08-04 jrmu (test-eval '(set! x -25) 'ok)
481 665c255d 2023-08-04 jrmu (test-eval 'x -25)
482 665c255d 2023-08-04 jrmu (geval '(define z (lambda (x y) (+ x (* x y)))))
483 665c255d 2023-08-04 jrmu (test-eval '(z 3 4) 15)
484 665c255d 2023-08-04 jrmu (test-eval '(cond ((= x -2) 'x=-2)
485 665c255d 2023-08-04 jrmu ((= x -25) 'x=-25)
486 665c255d 2023-08-04 jrmu (else 'failed))
488 665c255d 2023-08-04 jrmu (test-eval '(if true false true) false)
490 665c255d 2023-08-04 jrmu '(let ((x 4) (y 7))
491 665c255d 2023-08-04 jrmu (+ x y (* x y)))
492 665c255d 2023-08-04 jrmu (+ 4 7 (* 4 7)))
496 665c255d 2023-08-04 jrmu (geval '(define x (+ 3 8)))
497 665c255d 2023-08-04 jrmu (test-eval '(and 0 true x) 11)
498 665c255d 2023-08-04 jrmu (test-eval '(and 0 true x false) false)
499 665c255d 2023-08-04 jrmu (test-eval '(and 0 true x (set! x -2) false) false)
500 665c255d 2023-08-04 jrmu (test-eval 'x -2)
501 665c255d 2023-08-04 jrmu (test-eval '(and 0 true x false (set! x -5)) false)
502 665c255d 2023-08-04 jrmu (test-eval 'x -2)
503 665c255d 2023-08-04 jrmu (test-eval '(or false (set! x 25)) 'ok)
504 665c255d 2023-08-04 jrmu (test-eval 'x 25)
505 665c255d 2023-08-04 jrmu (test-eval '(or (set! x 2) (set! x 4)) 'ok)
506 665c255d 2023-08-04 jrmu (test-eval 'x 2)
507 665c255d 2023-08-04 jrmu (test-eval '(or false (set! x 25) true false) 'ok)
508 665c255d 2023-08-04 jrmu (test-eval 'x 25)
509 665c255d 2023-08-04 jrmu (test-eval '(or ((lambda (x) x) 5)) 5)
510 665c255d 2023-08-04 jrmu (test-eval '(or (begin (set! x (+ x 1)) x)) 26)
516 665c255d 2023-08-04 jrmu '(cond ((assoc 'b '((a 1) (b 2))) => cadr)
517 665c255d 2023-08-04 jrmu (else false))
521 665c255d 2023-08-04 jrmu '(cond ((= 3 4) 'not-true)
522 665c255d 2023-08-04 jrmu ((= (* 2 4) 3) 'also-false)
523 665c255d 2023-08-04 jrmu ((map (lambda (x)
524 665c255d 2023-08-04 jrmu (* x (+ x 1)))
525 665c255d 2023-08-04 jrmu '(2 4 1 9))
527 665c255d 2023-08-04 jrmu (lambda (x)
528 665c255d 2023-08-04 jrmu (accumulate + 0 x)))
529 665c255d 2023-08-04 jrmu (else 'never-reach))
531 665c255d 2023-08-04 jrmu ;; '(6 20 2 90)
534 665c255d 2023-08-04 jrmu ;; procedure definition and application
536 665c255d 2023-08-04 jrmu '(define (factorial n)
537 665c255d 2023-08-04 jrmu (if (= n 0)
539 665c255d 2023-08-04 jrmu (* n (factorial (- n 1))))))
540 665c255d 2023-08-04 jrmu (test-eval '(factorial 5) 120)
545 665c255d 2023-08-04 jrmu '(map (lambda (x)
546 665c255d 2023-08-04 jrmu (* x (+ x 1)))
547 665c255d 2023-08-04 jrmu '(2 1 4 2 8 3))
548 665c255d 2023-08-04 jrmu '(6 2 20 6 72 12))
549 665c255d 2023-08-04 jrmu ;; accumulate
552 665c255d 2023-08-04 jrmu '(accumulate + 0 '(1 2 3 4 5))
555 665c255d 2023-08-04 jrmu ;; make-let
557 665c255d 2023-08-04 jrmu (make-let '(x y) '(3 5) '((+ x y)))
564 665c255d 2023-08-04 jrmu '(let ((x 3))
568 665c255d 2023-08-04 jrmu '(let ((x 3)
573 665c255d 2023-08-04 jrmu '(let ((x 3)
575 665c255d 2023-08-04 jrmu (+ (let ((x (+ y 2))
579 665c255d 2023-08-04 jrmu (+ (* 4 3) 3 2))
581 665c255d 2023-08-04 jrmu '(let ((x 6)
582 665c255d 2023-08-04 jrmu (y (let ((x 2))
584 665c255d 2023-08-04 jrmu (z (let ((a (* 3 2)))
593 665c255d 2023-08-04 jrmu '(let* ((x 3)
594 665c255d 2023-08-04 jrmu (y (+ x 2))
595 665c255d 2023-08-04 jrmu (z (+ x y 5)))
604 665c255d 2023-08-04 jrmu '(let* ((x 3))
605 665c255d 2023-08-04 jrmu (let* ((y 5))
610 665c255d 2023-08-04 jrmu '(let* ((x 3)
611 665c255d 2023-08-04 jrmu (y (+ x 1)))
612 665c255d 2023-08-04 jrmu (+ (let* ((x (+ y 2))
616 665c255d 2023-08-04 jrmu (+ (* 6 6) 3 4))
618 665c255d 2023-08-04 jrmu '(let* ((x 6)
619 665c255d 2023-08-04 jrmu (y (let* ((x 2)
620 665c255d 2023-08-04 jrmu (a (let* ((x (* 3 x)))
623 665c255d 2023-08-04 jrmu (z (+ x y)))
627 665c255d 2023-08-04 jrmu ;; named-let
630 665c255d 2023-08-04 jrmu '(let eight ()
636 665c255d 2023-08-04 jrmu '(let loop ((count 0))
637 665c255d 2023-08-04 jrmu (if (= 100 count)
639 665c255d 2023-08-04 jrmu (loop (+ count 1))))
642 665c255d 2023-08-04 jrmu '(define (prime? x)
643 665c255d 2023-08-04 jrmu (let prime-iter ((i 2))
644 665c255d 2023-08-04 jrmu (cond ((> (* i i) x) true)
645 665c255d 2023-08-04 jrmu ((= (remainder x i) 0) false)
646 665c255d 2023-08-04 jrmu (else (prime-iter (+ i 1)))))))
648 665c255d 2023-08-04 jrmu '(let primes ((x 2)
650 665c255d 2023-08-04 jrmu (cond ((= n 0) '())
651 665c255d 2023-08-04 jrmu ((prime? x)
653 665c255d 2023-08-04 jrmu (primes (+ x 1) (- n 1))))
654 665c255d 2023-08-04 jrmu (else (primes (+ x 1) n))))
655 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))
658 665c255d 2023-08-04 jrmu '(define (fib n)
659 665c255d 2023-08-04 jrmu (let fib-iter ((a 1)
662 665c255d 2023-08-04 jrmu (if (= count 0)
664 665c255d 2023-08-04 jrmu (fib-iter (+ a b) a (- count 1))))))
665 665c255d 2023-08-04 jrmu (test-eval '(fib 19) 4181)
669 665c255d 2023-08-04 jrmu '(let ((y 0))
670 665c255d 2023-08-04 jrmu (do ((x 0 (+ x 1)))
671 665c255d 2023-08-04 jrmu ((= x 5) y)
672 665c255d 2023-08-04 jrmu (set! y (+ y 1))))
683 665c255d 2023-08-04 jrmu '(let ((y 0))
685 665c255d 2023-08-04 jrmu ((= y 5) y)
686 665c255d 2023-08-04 jrmu (set! y (+ y 1))))
690 665c255d 2023-08-04 jrmu '(do ((y '(1 2 3 4)))
691 665c255d 2023-08-04 jrmu ((null? y))
692 665c255d 2023-08-04 jrmu (set! y (cdr y)))
695 665c255d 2023-08-04 jrmu '(let ((y 0))
696 665c255d 2023-08-04 jrmu (do ((x 0 (+ x 1)))
697 665c255d 2023-08-04 jrmu ((= x 5) y)
698 665c255d 2023-08-04 jrmu (set! y (+ y 1))))
701 665c255d 2023-08-04 jrmu '(let ((x '(1 3 5 7 9)))
702 665c255d 2023-08-04 jrmu (do ((x x (cdr x))
703 665c255d 2023-08-04 jrmu (sum 0 (+ sum (car x))))
704 665c255d 2023-08-04 jrmu ((null? x) sum)))
707 665c255d 2023-08-04 jrmu '(let ((z '()))
708 665c255d 2023-08-04 jrmu (do ((x '(1 2 3 4) (cdr x))
709 665c255d 2023-08-04 jrmu (y '(1 2 3 4 5 6 7 8) (cddr y)))
710 665c255d 2023-08-04 jrmu ((null? x) y x z)
711 665c255d 2023-08-04 jrmu (set! z (cons (car x) z))))
712 665c255d 2023-08-04 jrmu '(4 3 2 1))
