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 ((letrec? exp) (eval (letrec->let exp) env))
24 665c255d 2023-08-04 jrmu ((do? exp) (eval (do->combination exp) env))
25 665c255d 2023-08-04 jrmu ((application? exp)
26 665c255d 2023-08-04 jrmu (apply (eval (operator exp) env)
27 665c255d 2023-08-04 jrmu (list-of-values (operands exp) env)))
29 665c255d 2023-08-04 jrmu (error "Unknown expression type -- EVAL" exp))))
30 665c255d 2023-08-04 jrmu (define (apply procedure arguments)
31 665c255d 2023-08-04 jrmu (cond ((primitive-procedure? procedure)
32 665c255d 2023-08-04 jrmu (apply-primitive-procedure procedure arguments))
33 665c255d 2023-08-04 jrmu ((compound-procedure? procedure)
34 665c255d 2023-08-04 jrmu (eval-sequence
35 665c255d 2023-08-04 jrmu (procedure-body procedure)
36 665c255d 2023-08-04 jrmu (extend-environment
37 665c255d 2023-08-04 jrmu (procedure-parameters procedure)
39 665c255d 2023-08-04 jrmu (procedure-environment procedure))))
42 665c255d 2023-08-04 jrmu "Unknown procedure type -- APPLY" procedure))))
44 665c255d 2023-08-04 jrmu (define (list-of-values exps env)
45 665c255d 2023-08-04 jrmu (if (no-operands? exps)
47 665c255d 2023-08-04 jrmu (cons (eval (first-operand exps) env)
48 665c255d 2023-08-04 jrmu (list-of-values (rest-operands exps) env))))
50 665c255d 2023-08-04 jrmu (define (tagged-list? exp tag)
51 665c255d 2023-08-04 jrmu (if (pair? exp)
52 665c255d 2023-08-04 jrmu (eq? (car exp) tag)
55 665c255d 2023-08-04 jrmu ;; self-evaluating/variable/quoted
56 665c255d 2023-08-04 jrmu (define (self-evaluating? exp)
57 665c255d 2023-08-04 jrmu (cond ((number? exp) true)
58 665c255d 2023-08-04 jrmu ((string? exp) true)
59 665c255d 2023-08-04 jrmu (else false)))
60 665c255d 2023-08-04 jrmu (define (variable? exp) (symbol? exp))
61 665c255d 2023-08-04 jrmu (define (quoted? exp)
62 665c255d 2023-08-04 jrmu (tagged-list? exp 'quote))
63 665c255d 2023-08-04 jrmu (define (text-of-quotation exp) (cadr exp))
65 665c255d 2023-08-04 jrmu ;; assignment/definition
66 665c255d 2023-08-04 jrmu (define (assignment? exp)
67 665c255d 2023-08-04 jrmu (tagged-list? exp 'set!))
68 665c255d 2023-08-04 jrmu (define (assignment-variable exp) (cadr exp))
69 665c255d 2023-08-04 jrmu (define (assignment-value exp) (caddr exp))
70 665c255d 2023-08-04 jrmu (define (make-assignment var val)
71 665c255d 2023-08-04 jrmu (list 'set! var val))
72 665c255d 2023-08-04 jrmu (define (definition? exp)
73 665c255d 2023-08-04 jrmu (tagged-list? exp 'define))
74 665c255d 2023-08-04 jrmu (define (definition-variable exp)
75 665c255d 2023-08-04 jrmu (if (symbol? (cadr exp))
77 665c255d 2023-08-04 jrmu (caadr exp)))
78 665c255d 2023-08-04 jrmu (define (definition-value exp)
79 665c255d 2023-08-04 jrmu (if (symbol? (cadr exp))
81 665c255d 2023-08-04 jrmu (make-lambda (cdadr exp) ; formal parameters
82 665c255d 2023-08-04 jrmu (cddr exp)))) ; body
83 665c255d 2023-08-04 jrmu (define (eval-assignment exp env)
84 665c255d 2023-08-04 jrmu (set-variable-value! (assignment-variable exp)
85 665c255d 2023-08-04 jrmu (eval (assignment-value exp) env)
88 665c255d 2023-08-04 jrmu (define (eval-definition exp env)
89 665c255d 2023-08-04 jrmu (define-variable! (definition-variable exp)
90 665c255d 2023-08-04 jrmu (eval (definition-value exp) env)
93 665c255d 2023-08-04 jrmu (define (make-definition var val)
94 665c255d 2023-08-04 jrmu `(define ,var ,val))
96 665c255d 2023-08-04 jrmu ;; make-unbound!
98 665c255d 2023-08-04 jrmu ;; (define (unbound? exp)
99 665c255d 2023-08-04 jrmu ;; (tagged-list? exp 'make-unbound!))
100 665c255d 2023-08-04 jrmu ;; (define (unbound-var exp)
101 665c255d 2023-08-04 jrmu ;; (cadr exp))
102 665c255d 2023-08-04 jrmu ;; (define (eval-unbound exp env)
103 665c255d 2023-08-04 jrmu ;; (remove-binding-from-frame! (unbound-var exp) (first-frame env)))
107 665c255d 2023-08-04 jrmu ;; if/and/or
108 665c255d 2023-08-04 jrmu (define (if? exp) (tagged-list? exp 'if))
109 665c255d 2023-08-04 jrmu (define (if-predicate exp) (cadr exp))
110 665c255d 2023-08-04 jrmu (define (if-consequent exp) (caddr exp))
111 665c255d 2023-08-04 jrmu (define (if-alternative exp)
112 665c255d 2023-08-04 jrmu (if (not (null? (cdddr exp)))
113 665c255d 2023-08-04 jrmu (cadddr exp)
115 665c255d 2023-08-04 jrmu (define (make-if predicate consequent alternative)
116 665c255d 2023-08-04 jrmu (list 'if predicate consequent alternative))
117 665c255d 2023-08-04 jrmu (define (eval-if exp env)
118 665c255d 2023-08-04 jrmu (if (true? (eval (if-predicate exp) env))
119 665c255d 2023-08-04 jrmu (eval (if-consequent exp) env)
120 665c255d 2023-08-04 jrmu (eval (if-alternative exp) env)))
122 665c255d 2023-08-04 jrmu (define (and? exp)
123 665c255d 2023-08-04 jrmu (tagged-list? exp 'and))
124 665c255d 2023-08-04 jrmu (define (and-clauses exp)
126 665c255d 2023-08-04 jrmu (define (or? exp)
127 665c255d 2023-08-04 jrmu (tagged-list? exp 'or))
128 665c255d 2023-08-04 jrmu (define (or-clauses exp)
130 665c255d 2023-08-04 jrmu (define (eval-and exp env)
131 665c255d 2023-08-04 jrmu (define (eval-clauses clauses)
132 665c255d 2023-08-04 jrmu (cond ((null? clauses) true)
133 665c255d 2023-08-04 jrmu ((null? (cdr clauses)) (eval (car clauses) env))
134 665c255d 2023-08-04 jrmu (else (and (eval (car clauses) env)
135 665c255d 2023-08-04 jrmu (eval-clauses (cdr clauses))))))
136 665c255d 2023-08-04 jrmu (eval-clauses (and-clauses exp)))
137 665c255d 2023-08-04 jrmu (define (eval-or exp env)
138 665c255d 2023-08-04 jrmu (define (eval-clauses clauses)
139 665c255d 2023-08-04 jrmu (if (null? clauses)
141 665c255d 2023-08-04 jrmu (or (eval (car clauses) env)
142 665c255d 2023-08-04 jrmu (eval-clauses (cdr clauses)))))
143 665c255d 2023-08-04 jrmu (eval-clauses (or-clauses exp)))
146 665c255d 2023-08-04 jrmu ;; lambda/let/let*/letrec
147 665c255d 2023-08-04 jrmu (define (lambda? exp) (tagged-list? exp 'lambda))
148 665c255d 2023-08-04 jrmu (define (lambda-parameters exp) (cadr exp))
149 665c255d 2023-08-04 jrmu (define (lambda-body exp) (cddr exp))
150 665c255d 2023-08-04 jrmu (define (make-lambda parameters body)
151 665c255d 2023-08-04 jrmu (cons 'lambda (cons parameters body)))
153 665c255d 2023-08-04 jrmu (define (make-let vars vals body)
155 665c255d 2023-08-04 jrmu (cons (map list vars vals)
157 665c255d 2023-08-04 jrmu (define (let? exp)
158 665c255d 2023-08-04 jrmu (and (tagged-list? exp 'let)
159 665c255d 2023-08-04 jrmu (not (symbol? (cadr exp)))))
160 665c255d 2023-08-04 jrmu (define (let-vars exp)
161 665c255d 2023-08-04 jrmu (map car (cadr exp)))
162 665c255d 2023-08-04 jrmu (define (let-vals exp)
163 665c255d 2023-08-04 jrmu (map cadr (cadr exp)))
164 665c255d 2023-08-04 jrmu (define (let-body exp)
165 665c255d 2023-08-04 jrmu (cddr exp))
166 665c255d 2023-08-04 jrmu (define (let->combination exp)
167 665c255d 2023-08-04 jrmu (make-application (make-lambda (let-vars exp) (let-body exp))
168 665c255d 2023-08-04 jrmu (let-vals exp)))
169 665c255d 2023-08-04 jrmu (define (named-let? exp)
170 665c255d 2023-08-04 jrmu (and (tagged-list? exp 'let)
171 665c255d 2023-08-04 jrmu (symbol? (cadr exp))))
172 665c255d 2023-08-04 jrmu (define (named-let-name exp)
173 665c255d 2023-08-04 jrmu (cadr exp))
174 665c255d 2023-08-04 jrmu (define (named-let-vars exp)
175 665c255d 2023-08-04 jrmu (map car (caddr exp)))
176 665c255d 2023-08-04 jrmu (define (named-let-vals exp)
177 665c255d 2023-08-04 jrmu (map cadr (caddr exp)))
178 665c255d 2023-08-04 jrmu (define (named-let-body exp)
179 665c255d 2023-08-04 jrmu (cdddr exp))
180 665c255d 2023-08-04 jrmu (define (named-let->combination exp)
181 665c255d 2023-08-04 jrmu (sequence->exp
182 665c255d 2023-08-04 jrmu (list (make-definition (named-let-name exp)
183 665c255d 2023-08-04 jrmu (make-lambda (named-let-vars exp)
184 665c255d 2023-08-04 jrmu (named-let-body exp)))
185 665c255d 2023-08-04 jrmu (make-application (named-let-name exp)
186 665c255d 2023-08-04 jrmu (named-let-vals exp)))))
187 665c255d 2023-08-04 jrmu (define (make-named-let name vars vals body)
190 665c255d 2023-08-04 jrmu (cons (map list vars vals)
193 665c255d 2023-08-04 jrmu (define (letrec? exp)
194 665c255d 2023-08-04 jrmu (tagged-list? exp 'letrec))
196 665c255d 2023-08-04 jrmu (define (letrec-vars exp)
197 665c255d 2023-08-04 jrmu (map car (cadr exp)))
198 665c255d 2023-08-04 jrmu (define (letrec-vals exp)
199 665c255d 2023-08-04 jrmu (map cadr (cadr exp)))
200 665c255d 2023-08-04 jrmu (define (letrec-body exp)
201 665c255d 2023-08-04 jrmu (cddr exp))
202 665c255d 2023-08-04 jrmu (define (letrec->let exp)
203 665c255d 2023-08-04 jrmu (let* ((vars (letrec-vars exp))
204 665c255d 2023-08-04 jrmu (unassigneds (map (lambda (var) ''*unassigned*)
206 665c255d 2023-08-04 jrmu (vals (letrec-vals exp))
207 665c255d 2023-08-04 jrmu (assignments (map (lambda (var val)
208 665c255d 2023-08-04 jrmu (make-assignment var val))
211 665c255d 2023-08-04 jrmu (body (letrec-body exp)))
212 665c255d 2023-08-04 jrmu (make-let vars
213 665c255d 2023-08-04 jrmu unassigneds
214 665c255d 2023-08-04 jrmu (append assignments body))))
219 665c255d 2023-08-04 jrmu (define (make-application op args)
220 665c255d 2023-08-04 jrmu (cons op args))
222 665c255d 2023-08-04 jrmu (define (let*? exp)
223 665c255d 2023-08-04 jrmu (tagged-list? exp 'let*))
224 665c255d 2023-08-04 jrmu (define let*-vars let-vars)
225 665c255d 2023-08-04 jrmu (define let*-vals let-vals)
226 665c255d 2023-08-04 jrmu (define let*-body let-body)
227 665c255d 2023-08-04 jrmu (define (let*->nested-lets exp)
228 665c255d 2023-08-04 jrmu (define (expand-lets vars vals)
229 665c255d 2023-08-04 jrmu (if (null? (cdr vars))
230 665c255d 2023-08-04 jrmu (make-let (list (car vars))
231 665c255d 2023-08-04 jrmu (list (car vals))
232 665c255d 2023-08-04 jrmu (let*-body exp))
233 665c255d 2023-08-04 jrmu (make-let (list (car vars))
234 665c255d 2023-08-04 jrmu (list (car vals))
235 665c255d 2023-08-04 jrmu (list (expand-lets (cdr vars) (cdr vals))))))
236 665c255d 2023-08-04 jrmu (let ((vars (let*-vars exp))
237 665c255d 2023-08-04 jrmu (vals (let*-vals exp)))
238 665c255d 2023-08-04 jrmu (if (null? vars)
239 665c255d 2023-08-04 jrmu (sequence->exp (let*-body exp))
240 665c255d 2023-08-04 jrmu (expand-lets vars vals))))
243 665c255d 2023-08-04 jrmu (define (do? exp)
244 665c255d 2023-08-04 jrmu (tagged-list? exp 'do))
245 665c255d 2023-08-04 jrmu (define (do-vars exp)
246 665c255d 2023-08-04 jrmu (map car (cadr exp)))
247 665c255d 2023-08-04 jrmu (define (do-inits exp)
248 665c255d 2023-08-04 jrmu (map cadr (cadr exp)))
249 665c255d 2023-08-04 jrmu (define (do-steps exp)
250 665c255d 2023-08-04 jrmu (map (lambda (var-init-step)
251 665c255d 2023-08-04 jrmu (if (null? (cddr var-init-step))
252 665c255d 2023-08-04 jrmu (car var-init-step)
253 665c255d 2023-08-04 jrmu (caddr var-init-step)))
254 665c255d 2023-08-04 jrmu (cadr exp)))
255 665c255d 2023-08-04 jrmu (define (do-test exp)
256 665c255d 2023-08-04 jrmu (caaddr exp))
257 665c255d 2023-08-04 jrmu (define (do-expressions exp)
258 665c255d 2023-08-04 jrmu (if (null? (cdaddr exp))
259 665c255d 2023-08-04 jrmu (caddr exp)
260 665c255d 2023-08-04 jrmu (cdaddr exp)))
261 665c255d 2023-08-04 jrmu (define (do-commands exp)
262 665c255d 2023-08-04 jrmu (cdddr exp))
263 665c255d 2023-08-04 jrmu (define (do->combination exp)
264 665c255d 2023-08-04 jrmu (make-named-let
266 665c255d 2023-08-04 jrmu (do-vars exp)
267 665c255d 2023-08-04 jrmu (do-inits exp)
270 665c255d 2023-08-04 jrmu (do-test exp)
271 665c255d 2023-08-04 jrmu (sequence->exp (do-expressions exp))
272 665c255d 2023-08-04 jrmu (sequence->exp
273 665c255d 2023-08-04 jrmu (append (do-commands exp)
274 665c255d 2023-08-04 jrmu (list (make-application
276 665c255d 2023-08-04 jrmu (do-steps exp)))))))))
279 665c255d 2023-08-04 jrmu ;; begin/sequence
280 665c255d 2023-08-04 jrmu (define (begin? exp) (tagged-list? exp 'begin))
281 665c255d 2023-08-04 jrmu (define (begin-actions exp) (cdr exp))
282 665c255d 2023-08-04 jrmu (define (last-exp? seq) (null? (cdr seq)))
283 665c255d 2023-08-04 jrmu (define (first-exp seq) (car seq))
284 665c255d 2023-08-04 jrmu (define (rest-exps seq) (cdr seq))
285 665c255d 2023-08-04 jrmu (define (sequence->exp seq)
286 665c255d 2023-08-04 jrmu (cond ((null? seq) seq)
287 665c255d 2023-08-04 jrmu ((last-exp? seq) (first-exp seq))
288 665c255d 2023-08-04 jrmu (else (make-begin seq))))
289 665c255d 2023-08-04 jrmu (define (make-begin seq) (cons 'begin seq))
290 665c255d 2023-08-04 jrmu (define (eval-sequence exps env)
291 665c255d 2023-08-04 jrmu (cond ((last-exp? exps) (eval (first-exp exps) env))
292 665c255d 2023-08-04 jrmu (else (eval (first-exp exps) env)
293 665c255d 2023-08-04 jrmu (eval-sequence (rest-exps exps) env))))
295 665c255d 2023-08-04 jrmu ;; application
296 665c255d 2023-08-04 jrmu (define (application? exp) (pair? exp))
297 665c255d 2023-08-04 jrmu (define (operator exp) (car exp))
298 665c255d 2023-08-04 jrmu (define (operands exp) (cdr exp))
299 665c255d 2023-08-04 jrmu (define (no-operands? ops) (null? ops))
300 665c255d 2023-08-04 jrmu (define (first-operand ops) (car ops))
301 665c255d 2023-08-04 jrmu (define (rest-operands ops) (cdr ops))
304 665c255d 2023-08-04 jrmu (define (cond? exp) (tagged-list? exp 'cond))
305 665c255d 2023-08-04 jrmu (define (cond-clauses exp) (cdr exp))
306 665c255d 2023-08-04 jrmu (define (cond-else-clause? clause)
307 665c255d 2023-08-04 jrmu (eq? (cond-predicate clause) 'else))
308 665c255d 2023-08-04 jrmu (define (cond-predicate clause) (car clause))
309 665c255d 2023-08-04 jrmu (define (cond-actions clause) (cdr clause))
310 665c255d 2023-08-04 jrmu (define (cond-extended-clause? clause)
311 665c255d 2023-08-04 jrmu (and (not (null? (cdr clause))) (eq? (cadr clause) '=>)))
312 665c255d 2023-08-04 jrmu (define (cond-extended-proc clause)
313 665c255d 2023-08-04 jrmu (caddr clause))
314 665c255d 2023-08-04 jrmu (define (cond->if exp)
315 665c255d 2023-08-04 jrmu (expand-clauses (cond-clauses exp)))
316 665c255d 2023-08-04 jrmu (define (expand-clauses clauses)
317 665c255d 2023-08-04 jrmu (if (null? clauses)
318 665c255d 2023-08-04 jrmu 'false ; no else clause
319 665c255d 2023-08-04 jrmu (let ((first (car clauses))
320 665c255d 2023-08-04 jrmu (rest (cdr clauses)))
321 665c255d 2023-08-04 jrmu (if (cond-else-clause? first)
322 665c255d 2023-08-04 jrmu (if (null? rest)
323 665c255d 2023-08-04 jrmu (sequence->exp (cond-actions first))
324 665c255d 2023-08-04 jrmu (error "ELSE clause isn't last -- COND->IF"
326 665c255d 2023-08-04 jrmu (if (cond-extended-clause? first)
327 665c255d 2023-08-04 jrmu (make-if (cond-predicate first)
328 665c255d 2023-08-04 jrmu (make-application
329 665c255d 2023-08-04 jrmu (cond-extended-proc first)
330 665c255d 2023-08-04 jrmu (list (cond-predicate first)))
331 665c255d 2023-08-04 jrmu (expand-clauses rest))
332 665c255d 2023-08-04 jrmu (make-if (cond-predicate first)
333 665c255d 2023-08-04 jrmu (sequence->exp (cond-actions first))
334 665c255d 2023-08-04 jrmu (expand-clauses rest)))))))
335 665c255d 2023-08-04 jrmu (define (true? x)
336 665c255d 2023-08-04 jrmu (not (eq? x false)))
337 665c255d 2023-08-04 jrmu (define (false? x)
338 665c255d 2023-08-04 jrmu (eq? x false))
340 665c255d 2023-08-04 jrmu ;; procedure
341 665c255d 2023-08-04 jrmu (define (make-procedure parameters body env)
342 665c255d 2023-08-04 jrmu (list 'procedure parameters body env))
343 665c255d 2023-08-04 jrmu ;; (define (scan-out-defines body)
344 665c255d 2023-08-04 jrmu ;; (let* ((definitions (filter definition? body))
345 665c255d 2023-08-04 jrmu ;; (vars (map definition-variable definitions))
346 665c255d 2023-08-04 jrmu ;; (unassigneds (map (lambda (var) ''*unassigned*)
348 665c255d 2023-08-04 jrmu ;; (vals (map definition-value definitions))
349 665c255d 2023-08-04 jrmu ;; (assignments
350 665c255d 2023-08-04 jrmu ;; (map (lambda (var val)
351 665c255d 2023-08-04 jrmu ;; (make-assignment var val))
352 665c255d 2023-08-04 jrmu ;; vars vals))
353 665c255d 2023-08-04 jrmu ;; (exps (remove definition? body)))
354 665c255d 2023-08-04 jrmu ;; (if (null? definitions)
357 665c255d 2023-08-04 jrmu ;; (make-let vars
358 665c255d 2023-08-04 jrmu ;; unassigneds
359 665c255d 2023-08-04 jrmu ;; (append assignments exps))))))
360 665c255d 2023-08-04 jrmu (define (compound-procedure? p)
361 665c255d 2023-08-04 jrmu (tagged-list? p 'procedure))
362 665c255d 2023-08-04 jrmu (define (procedure-parameters p) (cadr p))
363 665c255d 2023-08-04 jrmu (define (procedure-body p) (caddr p))
364 665c255d 2023-08-04 jrmu (define (procedure-environment p) (cadddr p))
366 665c255d 2023-08-04 jrmu ;; environment
367 665c255d 2023-08-04 jrmu (define (enclosing-environment env) (cdr env))
368 665c255d 2023-08-04 jrmu (define (first-frame env) (car env))
369 665c255d 2023-08-04 jrmu (define the-empty-environment '())
370 665c255d 2023-08-04 jrmu (define (make-frame variables values)
371 665c255d 2023-08-04 jrmu (cons variables values))
372 665c255d 2023-08-04 jrmu (define (frame-variables frame) (car frame))
373 665c255d 2023-08-04 jrmu (define (frame-values frame) (cdr frame))
374 665c255d 2023-08-04 jrmu (define (add-binding-to-frame! var val frame)
375 665c255d 2023-08-04 jrmu (set-car! frame (cons var (car frame)))
376 665c255d 2023-08-04 jrmu (set-cdr! frame (cons val (cdr frame))))
377 665c255d 2023-08-04 jrmu (define (extend-environment vars vals base-env)
378 665c255d 2023-08-04 jrmu (if (= (length vars) (length vals))
379 665c255d 2023-08-04 jrmu (cons (make-frame vars vals) base-env)
380 665c255d 2023-08-04 jrmu (if (< (length vars) (length vals))
381 665c255d 2023-08-04 jrmu (error "Too many arguments supplied" vars vals)
382 665c255d 2023-08-04 jrmu (error "Too few arguments supplied" vars vals))))
383 665c255d 2023-08-04 jrmu (define (lookup-variable-value var env)
384 665c255d 2023-08-04 jrmu (define (env-loop env)
385 665c255d 2023-08-04 jrmu (define (scan vars vals)
386 665c255d 2023-08-04 jrmu (cond ((null? vars)
387 665c255d 2023-08-04 jrmu (env-loop (enclosing-environment env)))
388 665c255d 2023-08-04 jrmu ((eq? var (car vars))
389 665c255d 2023-08-04 jrmu (let ((val (car vals)))
390 665c255d 2023-08-04 jrmu (if (eq? val '*unassigned*)
391 665c255d 2023-08-04 jrmu (error "Var not yet defined -- LOOKUP-VARIABLE-VALUE" var)
393 665c255d 2023-08-04 jrmu (else (scan (cdr vars) (cdr vals)))))
394 665c255d 2023-08-04 jrmu (if (eq? env the-empty-environment)
395 665c255d 2023-08-04 jrmu (error "Unbound variable" var)
396 665c255d 2023-08-04 jrmu (let ((frame (first-frame env)))
397 665c255d 2023-08-04 jrmu (scan (frame-variables frame)
398 665c255d 2023-08-04 jrmu (frame-values frame)))))
399 665c255d 2023-08-04 jrmu (env-loop env))
400 665c255d 2023-08-04 jrmu (define (set-variable-value! var val env)
401 665c255d 2023-08-04 jrmu (define (env-loop env)
402 665c255d 2023-08-04 jrmu (define (scan vars vals)
403 665c255d 2023-08-04 jrmu (cond ((null? vars)
404 665c255d 2023-08-04 jrmu (env-loop (enclosing-environment env)))
405 665c255d 2023-08-04 jrmu ((eq? var (car vars))
406 665c255d 2023-08-04 jrmu (set-car! vals val))
407 665c255d 2023-08-04 jrmu (else (scan (cdr vars) (cdr vals)))))
408 665c255d 2023-08-04 jrmu (if (eq? env the-empty-environment)
409 665c255d 2023-08-04 jrmu (error "Unbound variable -- SET!" var)
410 665c255d 2023-08-04 jrmu (let ((frame (first-frame env)))
411 665c255d 2023-08-04 jrmu (scan (frame-variables frame)
412 665c255d 2023-08-04 jrmu (frame-values frame)))))
413 665c255d 2023-08-04 jrmu (env-loop env))
414 665c255d 2023-08-04 jrmu (define (define-variable! var val env)
415 665c255d 2023-08-04 jrmu (let ((frame (first-frame env)))
416 665c255d 2023-08-04 jrmu (define (scan vars vals)
417 665c255d 2023-08-04 jrmu (cond ((null? vars)
418 665c255d 2023-08-04 jrmu (add-binding-to-frame! var val frame))
419 665c255d 2023-08-04 jrmu ((eq? var (car vars))
420 665c255d 2023-08-04 jrmu (set-car! vals val))
421 665c255d 2023-08-04 jrmu (else (scan (cdr vars) (cdr vals)))))
422 665c255d 2023-08-04 jrmu (scan (frame-variables frame)
423 665c255d 2023-08-04 jrmu (frame-values frame))))
425 665c255d 2023-08-04 jrmu (define (remove-binding-from-frame! var frame)
426 665c255d 2023-08-04 jrmu (define (scan vars vals)
427 665c255d 2023-08-04 jrmu (cond ((null? (cdr vars))
428 665c255d 2023-08-04 jrmu (error "Binding not found -- REMOVE-BINDING-FROM-FRAME!" var))
429 665c255d 2023-08-04 jrmu ((eq? var (cadr vars))
430 665c255d 2023-08-04 jrmu (set-cdr! vars (cddr vars))
431 665c255d 2023-08-04 jrmu (set-cdr! vals (cddr vals)))
432 665c255d 2023-08-04 jrmu (else (scan (cdr vars) (cdr vals)))))
433 665c255d 2023-08-04 jrmu (let ((vars (frame-variables frame))
434 665c255d 2023-08-04 jrmu (vals (frame-values frame)))
435 665c255d 2023-08-04 jrmu (if (eq? var (car vars))
436 665c255d 2023-08-04 jrmu (begin (set-car! frame (cdr vars))
437 665c255d 2023-08-04 jrmu (set-cdr! frame (cdr vals)))
438 665c255d 2023-08-04 jrmu (scan vars vals))))
440 665c255d 2023-08-04 jrmu ;; primitives
441 665c255d 2023-08-04 jrmu (define (primitive-procedure? proc)
442 665c255d 2023-08-04 jrmu (tagged-list? proc 'primitive))
443 665c255d 2023-08-04 jrmu (define (primitive-implementation proc) (cadr proc))
444 665c255d 2023-08-04 jrmu (define primitive-procedures
445 665c255d 2023-08-04 jrmu (list (list 'car car)
446 665c255d 2023-08-04 jrmu (list 'cdr cdr)
447 665c255d 2023-08-04 jrmu (list 'caar caar)
448 665c255d 2023-08-04 jrmu (list 'cadr cadr)
449 665c255d 2023-08-04 jrmu (list 'cddr cddr)
450 665c255d 2023-08-04 jrmu (list 'cons cons)
451 665c255d 2023-08-04 jrmu (list 'null? null?)
452 665c255d 2023-08-04 jrmu (list '* *)
453 665c255d 2023-08-04 jrmu (list '/ /)
454 665c255d 2023-08-04 jrmu (list '+ +)
455 665c255d 2023-08-04 jrmu (list '- -)
456 665c255d 2023-08-04 jrmu (list '= =)
457 665c255d 2023-08-04 jrmu (list '< <)
458 665c255d 2023-08-04 jrmu (list '> >)
459 665c255d 2023-08-04 jrmu (list '<= <=)
460 665c255d 2023-08-04 jrmu (list '>= >=)
461 665c255d 2023-08-04 jrmu (list 'remainder remainder)
462 665c255d 2023-08-04 jrmu (list 'eq? eq?)
463 665c255d 2023-08-04 jrmu (list 'equal? equal?)
464 665c255d 2023-08-04 jrmu (list 'display display)))
465 665c255d 2023-08-04 jrmu (define (primitive-procedure-names)
467 665c255d 2023-08-04 jrmu primitive-procedures))
468 665c255d 2023-08-04 jrmu (define (primitive-procedure-objects)
469 665c255d 2023-08-04 jrmu (map (lambda (proc) (list 'primitive (cadr proc)))
470 665c255d 2023-08-04 jrmu primitive-procedures))
471 665c255d 2023-08-04 jrmu (define (apply-primitive-procedure proc args)
472 665c255d 2023-08-04 jrmu (apply-in-underlying-scheme
473 665c255d 2023-08-04 jrmu (primitive-implementation proc) args))
475 665c255d 2023-08-04 jrmu ;; driver-loop
476 665c255d 2023-08-04 jrmu (define input-prompt ";;; M-Eval input:")
477 665c255d 2023-08-04 jrmu (define output-prompt ";;; M-Eval value:")
478 665c255d 2023-08-04 jrmu (define (driver-loop)
479 665c255d 2023-08-04 jrmu (prompt-for-input input-prompt)
480 665c255d 2023-08-04 jrmu (let ((input (read)))
481 665c255d 2023-08-04 jrmu (let ((output (eval input the-global-environment)))
482 665c255d 2023-08-04 jrmu (announce-output output-prompt)
483 665c255d 2023-08-04 jrmu (user-print output)))
484 665c255d 2023-08-04 jrmu (driver-loop))
485 665c255d 2023-08-04 jrmu (define (prompt-for-input string)
486 665c255d 2023-08-04 jrmu (newline) (newline) (display string) (newline))
488 665c255d 2023-08-04 jrmu (define (announce-output string)
489 665c255d 2023-08-04 jrmu (newline) (display string) (newline))
490 665c255d 2023-08-04 jrmu (define (user-print object)
491 665c255d 2023-08-04 jrmu (if (compound-procedure? object)
492 665c255d 2023-08-04 jrmu (display (list 'compound-procedure
493 665c255d 2023-08-04 jrmu (procedure-parameters object)
494 665c255d 2023-08-04 jrmu (procedure-body object)
495 665c255d 2023-08-04 jrmu '<procedure-env>))
496 665c255d 2023-08-04 jrmu (display object)))
497 665c255d 2023-08-04 jrmu (define (setup-environment)
498 665c255d 2023-08-04 jrmu (let ((initial-env
499 665c255d 2023-08-04 jrmu (extend-environment (primitive-procedure-names)
500 665c255d 2023-08-04 jrmu (primitive-procedure-objects)
501 665c255d 2023-08-04 jrmu the-empty-environment)))
502 665c255d 2023-08-04 jrmu (define-variable! 'true true initial-env)
503 665c255d 2023-08-04 jrmu (define-variable! 'false false initial-env)
504 665c255d 2023-08-04 jrmu initial-env))
505 665c255d 2023-08-04 jrmu (define the-global-environment (setup-environment))
507 665c255d 2023-08-04 jrmu ;; auxiliary
508 665c255d 2023-08-04 jrmu (define (test-case actual expected)
510 665c255d 2023-08-04 jrmu (display "Actual: ")
511 665c255d 2023-08-04 jrmu (display actual)
513 665c255d 2023-08-04 jrmu (display "Expected: ")
514 665c255d 2023-08-04 jrmu (display expected)
516 665c255d 2023-08-04 jrmu (define (geval exp) ;; eval globally
517 665c255d 2023-08-04 jrmu (eval exp the-global-environment))
518 665c255d 2023-08-04 jrmu (define (test-eval exp expected)
519 665c255d 2023-08-04 jrmu (test-case (geval exp) expected))
523 665c255d 2023-08-04 jrmu ;; test-suite
525 665c255d 2023-08-04 jrmu ;; procedure definitions
528 665c255d 2023-08-04 jrmu '(define (assoc key records)
529 665c255d 2023-08-04 jrmu (cond ((null? records) false)
530 665c255d 2023-08-04 jrmu ((equal? key (caar records)) (car records))
531 665c255d 2023-08-04 jrmu (else (assoc key (cdr records))))))
534 665c255d 2023-08-04 jrmu '(define (map proc list)
535 665c255d 2023-08-04 jrmu (if (null? list)
537 665c255d 2023-08-04 jrmu (cons (proc (car list))
538 665c255d 2023-08-04 jrmu (map proc (cdr list))))))
541 665c255d 2023-08-04 jrmu '(define (accumulate op initial sequence)
542 665c255d 2023-08-04 jrmu (if (null? sequence)
544 665c255d 2023-08-04 jrmu (op (car sequence)
545 665c255d 2023-08-04 jrmu (accumulate op initial (cdr sequence))))))
547 665c255d 2023-08-04 jrmu ;; all special forms
548 665c255d 2023-08-04 jrmu (test-eval '(begin 5 6) 6)
549 665c255d 2023-08-04 jrmu (test-eval '10 10)
550 665c255d 2023-08-04 jrmu (geval '(define x 3))
551 665c255d 2023-08-04 jrmu (test-eval 'x 3)
552 665c255d 2023-08-04 jrmu (test-eval '(set! x -25) 'ok)
553 665c255d 2023-08-04 jrmu (test-eval 'x -25)
554 665c255d 2023-08-04 jrmu (geval '(define z (lambda (x y) (+ x (* x y)))))
555 665c255d 2023-08-04 jrmu (test-eval '(z 3 4) 15)
556 665c255d 2023-08-04 jrmu (test-eval '(cond ((= x -2) 'x=-2)
557 665c255d 2023-08-04 jrmu ((= x -25) 'x=-25)
558 665c255d 2023-08-04 jrmu (else 'failed))
560 665c255d 2023-08-04 jrmu (test-eval '(if true false true) false)
563 665c255d 2023-08-04 jrmu '(let ((x 4) (y 7))
564 665c255d 2023-08-04 jrmu (+ x y (* x y)))
565 665c255d 2023-08-04 jrmu (+ 4 7 (* 4 7)))
569 665c255d 2023-08-04 jrmu (geval '(define x (+ 3 8)))
570 665c255d 2023-08-04 jrmu (test-eval '(and 0 true x) 11)
571 665c255d 2023-08-04 jrmu (test-eval '(and 0 true x false) false)
572 665c255d 2023-08-04 jrmu (test-eval '(and 0 true x (set! x -2) false) false)
573 665c255d 2023-08-04 jrmu (test-eval 'x -2)
574 665c255d 2023-08-04 jrmu (test-eval '(and 0 true x false (set! x -5)) false)
575 665c255d 2023-08-04 jrmu (test-eval 'x -2)
576 665c255d 2023-08-04 jrmu (test-eval '(or false (set! x 25)) 'ok)
577 665c255d 2023-08-04 jrmu (test-eval 'x 25)
578 665c255d 2023-08-04 jrmu (test-eval '(or (set! x 2) (set! x 4)) 'ok)
579 665c255d 2023-08-04 jrmu (test-eval 'x 2)
580 665c255d 2023-08-04 jrmu (test-eval '(or false (set! x 25) true false) 'ok)
581 665c255d 2023-08-04 jrmu (test-eval 'x 25)
582 665c255d 2023-08-04 jrmu (test-eval '(or ((lambda (x) x) 5)) 5)
583 665c255d 2023-08-04 jrmu (test-eval '(or (begin (set! x (+ x 1)) x)) 26)
589 665c255d 2023-08-04 jrmu '(cond ((assoc 'b '((a 1) (b 2))) => cadr)
590 665c255d 2023-08-04 jrmu (else false))
594 665c255d 2023-08-04 jrmu '(cond ((= 3 4) 'not-true)
595 665c255d 2023-08-04 jrmu ((= (* 2 4) 3) 'also-false)
596 665c255d 2023-08-04 jrmu ((map (lambda (x)
597 665c255d 2023-08-04 jrmu (* x (+ x 1)))
598 665c255d 2023-08-04 jrmu '(2 4 1 9))
600 665c255d 2023-08-04 jrmu (lambda (x)
601 665c255d 2023-08-04 jrmu (accumulate + 0 x)))
602 665c255d 2023-08-04 jrmu (else 'never-reach))
604 665c255d 2023-08-04 jrmu ;; '(6 20 2 90)
607 665c255d 2023-08-04 jrmu ;; procedure definition and application
609 665c255d 2023-08-04 jrmu '(define (factorial n)
610 665c255d 2023-08-04 jrmu (if (= n 0)
612 665c255d 2023-08-04 jrmu (* n (factorial (- n 1))))))
613 665c255d 2023-08-04 jrmu (test-eval '(factorial 5) 120)
618 665c255d 2023-08-04 jrmu '(map (lambda (x)
619 665c255d 2023-08-04 jrmu (* x (+ x 1)))
620 665c255d 2023-08-04 jrmu '(2 1 4 2 8 3))
621 665c255d 2023-08-04 jrmu '(6 2 20 6 72 12))
622 665c255d 2023-08-04 jrmu ;; accumulate
625 665c255d 2023-08-04 jrmu '(accumulate + 0 '(1 2 3 4 5))
628 665c255d 2023-08-04 jrmu ;; make-let
630 665c255d 2023-08-04 jrmu (make-let '(x y) '(3 5) '((+ x y)))
637 665c255d 2023-08-04 jrmu '(let ((x 3))
641 665c255d 2023-08-04 jrmu '(let ((x 3)
646 665c255d 2023-08-04 jrmu '(let ((x 3)
648 665c255d 2023-08-04 jrmu (+ (let ((x (+ y 2))
652 665c255d 2023-08-04 jrmu (+ (* 4 3) 3 2))
654 665c255d 2023-08-04 jrmu '(let ((x 6)
655 665c255d 2023-08-04 jrmu (y (let ((x 2))
657 665c255d 2023-08-04 jrmu (z (let ((a (* 3 2)))
666 665c255d 2023-08-04 jrmu '(let* ((x 3)
667 665c255d 2023-08-04 jrmu (y (+ x 2))
668 665c255d 2023-08-04 jrmu (z (+ x y 5)))
677 665c255d 2023-08-04 jrmu '(let* ((x 3))
678 665c255d 2023-08-04 jrmu (let* ((y 5))
683 665c255d 2023-08-04 jrmu '(let* ((x 3)
684 665c255d 2023-08-04 jrmu (y (+ x 1)))
685 665c255d 2023-08-04 jrmu (+ (let* ((x (+ y 2))
689 665c255d 2023-08-04 jrmu (+ (* 6 6) 3 4))
691 665c255d 2023-08-04 jrmu '(let* ((x 6)
692 665c255d 2023-08-04 jrmu (y (let* ((x 2)
693 665c255d 2023-08-04 jrmu (a (let* ((x (* 3 x)))
696 665c255d 2023-08-04 jrmu (z (+ x y)))
700 665c255d 2023-08-04 jrmu ;; named-let
703 665c255d 2023-08-04 jrmu '(let eight ()
709 665c255d 2023-08-04 jrmu '(let loop ((count 0))
710 665c255d 2023-08-04 jrmu (if (= 100 count)
712 665c255d 2023-08-04 jrmu (loop (+ count 1))))
715 665c255d 2023-08-04 jrmu '(define (prime? x)
716 665c255d 2023-08-04 jrmu (let prime-iter ((i 2))
717 665c255d 2023-08-04 jrmu (cond ((> (* i i) x) true)
718 665c255d 2023-08-04 jrmu ((= (remainder x i) 0) false)
719 665c255d 2023-08-04 jrmu (else (prime-iter (+ i 1)))))))
721 665c255d 2023-08-04 jrmu '(let primes ((x 2)
723 665c255d 2023-08-04 jrmu (cond ((= n 0) '())
724 665c255d 2023-08-04 jrmu ((prime? x)
726 665c255d 2023-08-04 jrmu (primes (+ x 1) (- n 1))))
727 665c255d 2023-08-04 jrmu (else (primes (+ x 1) n))))
728 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))
731 665c255d 2023-08-04 jrmu '(define (fib n)
732 665c255d 2023-08-04 jrmu (let fib-iter ((a 1)
735 665c255d 2023-08-04 jrmu (if (= count 0)
737 665c255d 2023-08-04 jrmu (fib-iter (+ a b) a (- count 1))))))
738 665c255d 2023-08-04 jrmu (test-eval '(fib 19) 4181)
742 665c255d 2023-08-04 jrmu '(let ((y 0))
743 665c255d 2023-08-04 jrmu (do ((x 0 (+ x 1)))
744 665c255d 2023-08-04 jrmu ((= x 5) y)
745 665c255d 2023-08-04 jrmu (set! y (+ y 1))))
756 665c255d 2023-08-04 jrmu '(let ((y 0))
758 665c255d 2023-08-04 jrmu ((= y 5) y)
759 665c255d 2023-08-04 jrmu (set! y (+ y 1))))
763 665c255d 2023-08-04 jrmu '(do ((y '(1 2 3 4)))
764 665c255d 2023-08-04 jrmu ((null? y))
765 665c255d 2023-08-04 jrmu (set! y (cdr y)))
768 665c255d 2023-08-04 jrmu '(let ((y 0))
769 665c255d 2023-08-04 jrmu (do ((x 0 (+ x 1)))
770 665c255d 2023-08-04 jrmu ((= x 5) y)
771 665c255d 2023-08-04 jrmu (set! y (+ y 1))))
774 665c255d 2023-08-04 jrmu '(let ((x '(1 3 5 7 9)))
775 665c255d 2023-08-04 jrmu (do ((x x (cdr x))
776 665c255d 2023-08-04 jrmu (sum 0 (+ sum (car x))))
777 665c255d 2023-08-04 jrmu ((null? x) sum)))
780 665c255d 2023-08-04 jrmu '(let ((z '()))
781 665c255d 2023-08-04 jrmu (do ((x '(1 2 3 4) (cdr x))
782 665c255d 2023-08-04 jrmu (y '(1 2 3 4 5 6 7 8) (cddr y)))
783 665c255d 2023-08-04 jrmu ((null? x) y x z)
784 665c255d 2023-08-04 jrmu (set! z (cons (car x) z))))
785 665c255d 2023-08-04 jrmu '(4 3 2 1))
789 665c255d 2023-08-04 jrmu ;; make-unbound!
790 665c255d 2023-08-04 jrmu ;; broken now due to scan-out-defines
792 665c255d 2023-08-04 jrmu ;; (test-eval
793 665c255d 2023-08-04 jrmu ;; '(let ((x 3))
794 665c255d 2023-08-04 jrmu ;; (let ((x 5))
795 665c255d 2023-08-04 jrmu ;; (make-unbound! x)
796 665c255d 2023-08-04 jrmu ;; (* x x)))
799 665c255d 2023-08-04 jrmu ;; (test-eval
800 665c255d 2023-08-04 jrmu ;; '(let ((x 3))
801 665c255d 2023-08-04 jrmu ;; (let ((x 5))
802 665c255d 2023-08-04 jrmu ;; (define y x)
803 665c255d 2023-08-04 jrmu ;; (make-unbound! x)
804 665c255d 2023-08-04 jrmu ;; (* y x)))
807 665c255d 2023-08-04 jrmu ;; (test-eval
808 665c255d 2023-08-04 jrmu ;; '(let ((y -1) (x 3))
809 665c255d 2023-08-04 jrmu ;; (let ((y 0.5) (x 5))
810 665c255d 2023-08-04 jrmu ;; (define a x)
811 665c255d 2023-08-04 jrmu ;; (define b y)
812 665c255d 2023-08-04 jrmu ;; (make-unbound! x)
813 665c255d 2023-08-04 jrmu ;; (make-unbound! y)
814 665c255d 2023-08-04 jrmu ;; (* a b x y)))
815 665c255d 2023-08-04 jrmu ;; (* 5 3 -1 0.5))
817 665c255d 2023-08-04 jrmu ;; (test-eval
818 665c255d 2023-08-04 jrmu ;; '(let ((x 3) (y 4))
819 665c255d 2023-08-04 jrmu ;; (let ((x 5))
820 665c255d 2023-08-04 jrmu ;; (make-unbound! x)
821 665c255d 2023-08-04 jrmu ;; (+ x 4)))
824 665c255d 2023-08-04 jrmu ;; (test-eval
825 665c255d 2023-08-04 jrmu ;; '(let ((a 1) (b 2) (c 3) (d 4))
826 665c255d 2023-08-04 jrmu ;; (make-unbound! b)
827 665c255d 2023-08-04 jrmu ;; (+ a c d))
828 665c255d 2023-08-04 jrmu ;; (+ 1 3 4))
830 665c255d 2023-08-04 jrmu ;; (test-eval
831 665c255d 2023-08-04 jrmu ;; '(let ((x 4) (y 5))
832 665c255d 2023-08-04 jrmu ;; (let ((a 1) (b 2) (c 3))
833 665c255d 2023-08-04 jrmu ;; (let ((x (+ a b)) (y (+ c a)))
834 665c255d 2023-08-04 jrmu ;; (make-unbound! x)
835 665c255d 2023-08-04 jrmu ;; (let ((a x) (b (+ x y)))
836 665c255d 2023-08-04 jrmu ;; (define z b)
837 665c255d 2023-08-04 jrmu ;; (make-unbound! b)
838 665c255d 2023-08-04 jrmu ;; (* (+ a z)
839 665c255d 2023-08-04 jrmu ;; (+ a b y))))))
840 665c255d 2023-08-04 jrmu ;; (* (+ 4 8)
841 665c255d 2023-08-04 jrmu ;; (+ 4 2 4)))
843 665c255d 2023-08-04 jrmu ;; x 3 -- y 4
844 665c255d 2023-08-04 jrmu ;; x 4 -- y 4
845 665c255d 2023-08-04 jrmu ;; a 4 -- b 4
846 665c255d 2023-08-04 jrmu ;; a 4 -- b 2
848 665c255d 2023-08-04 jrmu ;; scan-out-defines
851 665c255d 2023-08-04 jrmu '(define (f x)
852 665c255d 2023-08-04 jrmu (define (even? n)
853 665c255d 2023-08-04 jrmu (if (= n 0)
855 665c255d 2023-08-04 jrmu (odd? (- n 1))))
856 665c255d 2023-08-04 jrmu (define (odd? n)
857 665c255d 2023-08-04 jrmu (if (= n 0)
859 665c255d 2023-08-04 jrmu (even? (- n 1))))
860 665c255d 2023-08-04 jrmu (even? x)))
861 665c255d 2023-08-04 jrmu (test-eval '(f 5) false)
862 665c255d 2023-08-04 jrmu (test-eval '(f 10) true)
865 665c255d 2023-08-04 jrmu ;; '(let ((x 5))
866 665c255d 2023-08-04 jrmu ;; (define y x)
867 665c255d 2023-08-04 jrmu ;; (define x 3)
868 665c255d 2023-08-04 jrmu ;; (+ x y)))
869 665c255d 2023-08-04 jrmu ;; signal an error because x is undefined if variables are scanned out
874 665c255d 2023-08-04 jrmu '(define (f x)
875 665c255d 2023-08-04 jrmu (letrec ((even?
876 665c255d 2023-08-04 jrmu (lambda (n)
877 665c255d 2023-08-04 jrmu (if (= n 0)
879 665c255d 2023-08-04 jrmu (odd? (- n 1)))))
881 665c255d 2023-08-04 jrmu (lambda (n)
882 665c255d 2023-08-04 jrmu (if (= n 0)
884 665c255d 2023-08-04 jrmu (even? (- n 1))))))
885 665c255d 2023-08-04 jrmu (even? x))))
886 665c255d 2023-08-04 jrmu (test-eval '(f 11) false)
887 665c255d 2023-08-04 jrmu (test-eval '(f 16) true)
890 665c255d 2023-08-04 jrmu '(letrec ((fact
891 665c255d 2023-08-04 jrmu (lambda (n)
892 665c255d 2023-08-04 jrmu (if (= n 1)
894 665c255d 2023-08-04 jrmu (* n (fact (- n 1)))))))
