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 ((analyze exp) env))
7 665c255d 2023-08-04 jrmu (define (eval exp env)
8 665c255d 2023-08-04 jrmu (cond ((self-evaluating? exp) exp)
9 665c255d 2023-08-04 jrmu ((variable? exp) (lookup-variable-value exp env))
10 665c255d 2023-08-04 jrmu ((quoted? exp) (text-of-quotation exp))
11 665c255d 2023-08-04 jrmu ((assignment? exp) (eval-assignment exp env))
12 665c255d 2023-08-04 jrmu ((definition? exp) (eval-definition exp env))
13 665c255d 2023-08-04 jrmu ;; ((unbound? exp) (eval-unbound exp env))
14 665c255d 2023-08-04 jrmu ((if? exp) (eval-if exp env))
15 665c255d 2023-08-04 jrmu ((and? exp) (eval-and exp env))
16 665c255d 2023-08-04 jrmu ((or? exp) (eval-or exp env))
17 665c255d 2023-08-04 jrmu ((lambda? exp)
18 665c255d 2023-08-04 jrmu (make-procedure (lambda-parameters exp)
19 665c255d 2023-08-04 jrmu (lambda-body exp)
21 665c255d 2023-08-04 jrmu ((begin? exp)
22 665c255d 2023-08-04 jrmu (eval-sequence (begin-actions exp) env))
23 665c255d 2023-08-04 jrmu ((cond? exp) (eval (cond->if exp) env))
24 665c255d 2023-08-04 jrmu ((let? exp) (eval (let->combination exp) env))
25 665c255d 2023-08-04 jrmu ((let*? exp) (eval (let*->nested-lets exp) env))
26 665c255d 2023-08-04 jrmu ((named-let? exp) (eval (named-let->combination exp) env))
27 665c255d 2023-08-04 jrmu ((letrec? exp) (eval (letrec->let exp) env))
28 665c255d 2023-08-04 jrmu ((do? exp) (eval (do->combination exp) env))
29 665c255d 2023-08-04 jrmu ((application? exp)
30 665c255d 2023-08-04 jrmu (apply (eval (operator exp) env)
31 665c255d 2023-08-04 jrmu (list-of-values (operands exp) env)))
33 665c255d 2023-08-04 jrmu (error "Unknown expression type -- EVAL" exp))))
34 665c255d 2023-08-04 jrmu (define (apply procedure arguments)
35 665c255d 2023-08-04 jrmu (cond ((primitive-procedure? procedure)
36 665c255d 2023-08-04 jrmu (apply-primitive-procedure procedure arguments))
37 665c255d 2023-08-04 jrmu ((compound-procedure? procedure)
38 665c255d 2023-08-04 jrmu (eval-sequence
39 665c255d 2023-08-04 jrmu (procedure-body procedure)
40 665c255d 2023-08-04 jrmu (extend-environment
41 665c255d 2023-08-04 jrmu (procedure-parameters procedure)
43 665c255d 2023-08-04 jrmu (procedure-environment procedure))))
46 665c255d 2023-08-04 jrmu "Unknown procedure type -- APPLY" procedure))))
48 665c255d 2023-08-04 jrmu (define (list-of-values exps env)
49 665c255d 2023-08-04 jrmu (if (no-operands? exps)
51 665c255d 2023-08-04 jrmu (cons (eval (first-operand exps) env)
52 665c255d 2023-08-04 jrmu (list-of-values (rest-operands exps) env))))
54 665c255d 2023-08-04 jrmu (define (tagged-list? exp tag)
55 665c255d 2023-08-04 jrmu (if (pair? exp)
56 665c255d 2023-08-04 jrmu (eq? (car exp) tag)
59 665c255d 2023-08-04 jrmu ;; self-evaluating/variable/quoted
60 665c255d 2023-08-04 jrmu (define (self-evaluating? exp)
61 665c255d 2023-08-04 jrmu (cond ((number? exp) true)
62 665c255d 2023-08-04 jrmu ((string? exp) true)
63 665c255d 2023-08-04 jrmu (else false)))
64 665c255d 2023-08-04 jrmu (define (variable? exp) (symbol? exp))
65 665c255d 2023-08-04 jrmu (define (quoted? exp)
66 665c255d 2023-08-04 jrmu (tagged-list? exp 'quote))
67 665c255d 2023-08-04 jrmu (define (text-of-quotation exp) (cadr exp))
69 665c255d 2023-08-04 jrmu ;; assignment/definition
70 665c255d 2023-08-04 jrmu (define (assignment? exp)
71 665c255d 2023-08-04 jrmu (tagged-list? exp 'set!))
72 665c255d 2023-08-04 jrmu (define (assignment-variable exp) (cadr exp))
73 665c255d 2023-08-04 jrmu (define (assignment-value exp) (caddr exp))
74 665c255d 2023-08-04 jrmu (define (make-assignment var val)
75 665c255d 2023-08-04 jrmu (list 'set! var val))
76 665c255d 2023-08-04 jrmu (define (definition? exp)
77 665c255d 2023-08-04 jrmu (tagged-list? exp 'define))
78 665c255d 2023-08-04 jrmu (define (definition-variable exp)
79 665c255d 2023-08-04 jrmu (if (symbol? (cadr exp))
81 665c255d 2023-08-04 jrmu (caadr exp)))
82 665c255d 2023-08-04 jrmu (define (definition-value exp)
83 665c255d 2023-08-04 jrmu (if (symbol? (cadr exp))
85 665c255d 2023-08-04 jrmu (make-lambda (cdadr exp) ; formal parameters
86 665c255d 2023-08-04 jrmu (cddr exp)))) ; body
87 665c255d 2023-08-04 jrmu (define (eval-assignment exp env)
88 665c255d 2023-08-04 jrmu (set-variable-value! (assignment-variable exp)
89 665c255d 2023-08-04 jrmu (eval (assignment-value exp) env)
92 665c255d 2023-08-04 jrmu (define (eval-definition exp env)
93 665c255d 2023-08-04 jrmu (define-variable! (definition-variable exp)
94 665c255d 2023-08-04 jrmu (eval (definition-value exp) env)
97 665c255d 2023-08-04 jrmu (define (make-definition var val)
98 665c255d 2023-08-04 jrmu `(define ,var ,val))
100 665c255d 2023-08-04 jrmu ;; make-unbound!
102 665c255d 2023-08-04 jrmu ;; (define (unbound? exp)
103 665c255d 2023-08-04 jrmu ;; (tagged-list? exp 'make-unbound!))
104 665c255d 2023-08-04 jrmu ;; (define (unbound-var exp)
105 665c255d 2023-08-04 jrmu ;; (cadr exp))
106 665c255d 2023-08-04 jrmu ;; (define (eval-unbound exp env)
107 665c255d 2023-08-04 jrmu ;; (remove-binding-from-frame! (unbound-var exp) (first-frame env)))
111 665c255d 2023-08-04 jrmu ;; if/and/or
112 665c255d 2023-08-04 jrmu (define (if? exp) (tagged-list? exp 'if))
113 665c255d 2023-08-04 jrmu (define (if-predicate exp) (cadr exp))
114 665c255d 2023-08-04 jrmu (define (if-consequent exp) (caddr exp))
115 665c255d 2023-08-04 jrmu (define (if-alternative exp)
116 665c255d 2023-08-04 jrmu (if (not (null? (cdddr exp)))
117 665c255d 2023-08-04 jrmu (cadddr exp)
119 665c255d 2023-08-04 jrmu (define (make-if predicate consequent alternative)
120 665c255d 2023-08-04 jrmu (list 'if predicate consequent alternative))
121 665c255d 2023-08-04 jrmu (define (eval-if exp env)
122 665c255d 2023-08-04 jrmu (if (true? (eval (if-predicate exp) env))
123 665c255d 2023-08-04 jrmu (eval (if-consequent exp) env)
124 665c255d 2023-08-04 jrmu (eval (if-alternative exp) env)))
126 665c255d 2023-08-04 jrmu (define (and? exp)
127 665c255d 2023-08-04 jrmu (tagged-list? exp 'and))
128 665c255d 2023-08-04 jrmu (define (and-clauses exp)
130 665c255d 2023-08-04 jrmu (define (or? exp)
131 665c255d 2023-08-04 jrmu (tagged-list? exp 'or))
132 665c255d 2023-08-04 jrmu (define (or-clauses exp)
134 665c255d 2023-08-04 jrmu (define (eval-and exp env)
135 665c255d 2023-08-04 jrmu (define (eval-clauses clauses)
136 665c255d 2023-08-04 jrmu (cond ((null? clauses) true)
137 665c255d 2023-08-04 jrmu ((null? (cdr clauses)) (eval (car clauses) env))
138 665c255d 2023-08-04 jrmu (else (and (eval (car clauses) env)
139 665c255d 2023-08-04 jrmu (eval-clauses (cdr clauses))))))
140 665c255d 2023-08-04 jrmu (eval-clauses (and-clauses exp)))
141 665c255d 2023-08-04 jrmu (define (eval-or exp env)
142 665c255d 2023-08-04 jrmu (define (eval-clauses clauses)
143 665c255d 2023-08-04 jrmu (if (null? clauses)
145 665c255d 2023-08-04 jrmu (or (eval (car clauses) env)
146 665c255d 2023-08-04 jrmu (eval-clauses (cdr clauses)))))
147 665c255d 2023-08-04 jrmu (eval-clauses (or-clauses exp)))
150 665c255d 2023-08-04 jrmu ;; lambda/let/let*/letrec
151 665c255d 2023-08-04 jrmu (define (lambda? exp) (tagged-list? exp 'lambda))
152 665c255d 2023-08-04 jrmu (define (lambda-parameters exp) (cadr exp))
153 665c255d 2023-08-04 jrmu (define (lambda-body exp) (cddr exp))
154 665c255d 2023-08-04 jrmu (define (make-lambda parameters body)
155 665c255d 2023-08-04 jrmu (cons 'lambda (cons parameters body)))
157 665c255d 2023-08-04 jrmu (define (make-let vars vals body)
159 665c255d 2023-08-04 jrmu (cons (map list vars vals)
161 665c255d 2023-08-04 jrmu (define (let? exp)
162 665c255d 2023-08-04 jrmu (and (tagged-list? exp 'let)
163 665c255d 2023-08-04 jrmu (not (symbol? (cadr exp)))))
164 665c255d 2023-08-04 jrmu (define (let-vars exp)
165 665c255d 2023-08-04 jrmu (map car (cadr exp)))
166 665c255d 2023-08-04 jrmu (define (let-vals exp)
167 665c255d 2023-08-04 jrmu (map cadr (cadr exp)))
168 665c255d 2023-08-04 jrmu (define (let-body exp)
169 665c255d 2023-08-04 jrmu (cddr exp))
170 665c255d 2023-08-04 jrmu (define (let->combination exp)
171 665c255d 2023-08-04 jrmu (make-application (make-lambda (let-vars exp) (let-body exp))
172 665c255d 2023-08-04 jrmu (let-vals exp)))
173 665c255d 2023-08-04 jrmu (define (named-let? exp)
174 665c255d 2023-08-04 jrmu (and (tagged-list? exp 'let)
175 665c255d 2023-08-04 jrmu (symbol? (cadr exp))))
176 665c255d 2023-08-04 jrmu (define (named-let-name exp)
177 665c255d 2023-08-04 jrmu (cadr exp))
178 665c255d 2023-08-04 jrmu (define (named-let-vars exp)
179 665c255d 2023-08-04 jrmu (map car (caddr exp)))
180 665c255d 2023-08-04 jrmu (define (named-let-vals exp)
181 665c255d 2023-08-04 jrmu (map cadr (caddr exp)))
182 665c255d 2023-08-04 jrmu (define (named-let-body exp)
183 665c255d 2023-08-04 jrmu (cdddr exp))
184 665c255d 2023-08-04 jrmu (define (named-let->combination exp)
185 665c255d 2023-08-04 jrmu (sequence->exp
186 665c255d 2023-08-04 jrmu (list (make-definition (named-let-name exp)
187 665c255d 2023-08-04 jrmu (make-lambda (named-let-vars exp)
188 665c255d 2023-08-04 jrmu (named-let-body exp)))
189 665c255d 2023-08-04 jrmu (make-application (named-let-name exp)
190 665c255d 2023-08-04 jrmu (named-let-vals exp)))))
191 665c255d 2023-08-04 jrmu (define (make-named-let name vars vals body)
194 665c255d 2023-08-04 jrmu (cons (map list vars vals)
197 665c255d 2023-08-04 jrmu (define (letrec? exp)
198 665c255d 2023-08-04 jrmu (tagged-list? exp 'letrec))
200 665c255d 2023-08-04 jrmu (define (letrec-vars exp)
201 665c255d 2023-08-04 jrmu (map car (cadr exp)))
202 665c255d 2023-08-04 jrmu (define (letrec-vals exp)
203 665c255d 2023-08-04 jrmu (map cadr (cadr exp)))
204 665c255d 2023-08-04 jrmu (define (letrec-body exp)
205 665c255d 2023-08-04 jrmu (cddr exp))
206 665c255d 2023-08-04 jrmu (define (letrec->let exp)
207 665c255d 2023-08-04 jrmu (let* ((vars (letrec-vars exp))
208 665c255d 2023-08-04 jrmu (unassigneds (map (lambda (var) ''*unassigned*)
210 665c255d 2023-08-04 jrmu (vals (letrec-vals exp))
211 665c255d 2023-08-04 jrmu (assignments (map (lambda (var val)
212 665c255d 2023-08-04 jrmu (make-assignment var val))
215 665c255d 2023-08-04 jrmu (body (letrec-body exp)))
216 665c255d 2023-08-04 jrmu (make-let vars
217 665c255d 2023-08-04 jrmu unassigneds
218 665c255d 2023-08-04 jrmu (append assignments body))))
223 665c255d 2023-08-04 jrmu (define (make-application op args)
224 665c255d 2023-08-04 jrmu (cons op args))
226 665c255d 2023-08-04 jrmu (define (let*? exp)
227 665c255d 2023-08-04 jrmu (tagged-list? exp 'let*))
228 665c255d 2023-08-04 jrmu (define let*-vars let-vars)
229 665c255d 2023-08-04 jrmu (define let*-vals let-vals)
230 665c255d 2023-08-04 jrmu (define let*-body let-body)
231 665c255d 2023-08-04 jrmu (define (let*->nested-lets exp)
232 665c255d 2023-08-04 jrmu (define (expand-lets vars vals)
233 665c255d 2023-08-04 jrmu (if (null? (cdr vars))
234 665c255d 2023-08-04 jrmu (make-let (list (car vars))
235 665c255d 2023-08-04 jrmu (list (car vals))
236 665c255d 2023-08-04 jrmu (let*-body exp))
237 665c255d 2023-08-04 jrmu (make-let (list (car vars))
238 665c255d 2023-08-04 jrmu (list (car vals))
239 665c255d 2023-08-04 jrmu (list (expand-lets (cdr vars) (cdr vals))))))
240 665c255d 2023-08-04 jrmu (let ((vars (let*-vars exp))
241 665c255d 2023-08-04 jrmu (vals (let*-vals exp)))
242 665c255d 2023-08-04 jrmu (if (null? vars)
243 665c255d 2023-08-04 jrmu (sequence->exp (let*-body exp))
244 665c255d 2023-08-04 jrmu (expand-lets vars vals))))
247 665c255d 2023-08-04 jrmu (define (do? exp)
248 665c255d 2023-08-04 jrmu (tagged-list? exp 'do))
249 665c255d 2023-08-04 jrmu (define (do-vars exp)
250 665c255d 2023-08-04 jrmu (map car (cadr exp)))
251 665c255d 2023-08-04 jrmu (define (do-inits exp)
252 665c255d 2023-08-04 jrmu (map cadr (cadr exp)))
253 665c255d 2023-08-04 jrmu (define (do-steps exp)
254 665c255d 2023-08-04 jrmu (map (lambda (var-init-step)
255 665c255d 2023-08-04 jrmu (if (null? (cddr var-init-step))
256 665c255d 2023-08-04 jrmu (car var-init-step)
257 665c255d 2023-08-04 jrmu (caddr var-init-step)))
258 665c255d 2023-08-04 jrmu (cadr exp)))
259 665c255d 2023-08-04 jrmu (define (do-test exp)
260 665c255d 2023-08-04 jrmu (caaddr exp))
261 665c255d 2023-08-04 jrmu (define (do-expressions exp)
262 665c255d 2023-08-04 jrmu (if (null? (cdaddr exp))
263 665c255d 2023-08-04 jrmu (caddr exp)
264 665c255d 2023-08-04 jrmu (cdaddr exp)))
265 665c255d 2023-08-04 jrmu (define (do-commands exp)
266 665c255d 2023-08-04 jrmu (cdddr exp))
267 665c255d 2023-08-04 jrmu (define (do->combination exp)
268 665c255d 2023-08-04 jrmu (make-named-let
270 665c255d 2023-08-04 jrmu (do-vars exp)
271 665c255d 2023-08-04 jrmu (do-inits exp)
274 665c255d 2023-08-04 jrmu (do-test exp)
275 665c255d 2023-08-04 jrmu (sequence->exp (do-expressions exp))
276 665c255d 2023-08-04 jrmu (sequence->exp
277 665c255d 2023-08-04 jrmu (append (do-commands exp)
278 665c255d 2023-08-04 jrmu (list (make-application
280 665c255d 2023-08-04 jrmu (do-steps exp)))))))))
283 665c255d 2023-08-04 jrmu ;; begin/sequence
284 665c255d 2023-08-04 jrmu (define (begin? exp) (tagged-list? exp 'begin))
285 665c255d 2023-08-04 jrmu (define (begin-actions exp) (cdr exp))
286 665c255d 2023-08-04 jrmu (define (last-exp? seq) (null? (cdr seq)))
287 665c255d 2023-08-04 jrmu (define (first-exp seq) (car seq))
288 665c255d 2023-08-04 jrmu (define (rest-exps seq) (cdr seq))
289 665c255d 2023-08-04 jrmu (define (sequence->exp seq)
290 665c255d 2023-08-04 jrmu (cond ((null? seq) seq)
291 665c255d 2023-08-04 jrmu ((last-exp? seq) (first-exp seq))
292 665c255d 2023-08-04 jrmu (else (make-begin seq))))
293 665c255d 2023-08-04 jrmu (define (make-begin seq) (cons 'begin seq))
294 665c255d 2023-08-04 jrmu (define (eval-sequence exps env)
295 665c255d 2023-08-04 jrmu (cond ((last-exp? exps) (eval (first-exp exps) env))
296 665c255d 2023-08-04 jrmu (else (eval (first-exp exps) env)
297 665c255d 2023-08-04 jrmu (eval-sequence (rest-exps exps) env))))
299 665c255d 2023-08-04 jrmu ;; application
300 665c255d 2023-08-04 jrmu (define (application? exp) (pair? exp))
301 665c255d 2023-08-04 jrmu (define (operator exp) (car exp))
302 665c255d 2023-08-04 jrmu (define (operands exp) (cdr exp))
303 665c255d 2023-08-04 jrmu (define (no-operands? ops) (null? ops))
304 665c255d 2023-08-04 jrmu (define (first-operand ops) (car ops))
305 665c255d 2023-08-04 jrmu (define (rest-operands ops) (cdr ops))
308 665c255d 2023-08-04 jrmu (define (cond? exp) (tagged-list? exp 'cond))
309 665c255d 2023-08-04 jrmu (define (cond-clauses exp) (cdr exp))
310 665c255d 2023-08-04 jrmu (define (cond-else-clause? clause)
311 665c255d 2023-08-04 jrmu (eq? (cond-predicate clause) 'else))
312 665c255d 2023-08-04 jrmu (define (cond-predicate clause) (car clause))
313 665c255d 2023-08-04 jrmu (define (cond-actions clause) (cdr clause))
314 665c255d 2023-08-04 jrmu (define (cond-extended-clause? clause)
315 665c255d 2023-08-04 jrmu (and (not (null? (cdr clause))) (eq? (cadr clause) '=>)))
316 665c255d 2023-08-04 jrmu (define (cond-extended-proc clause)
317 665c255d 2023-08-04 jrmu (caddr clause))
318 665c255d 2023-08-04 jrmu (define (cond->if exp)
319 665c255d 2023-08-04 jrmu (expand-clauses (cond-clauses exp)))
320 665c255d 2023-08-04 jrmu (define (expand-clauses clauses)
321 665c255d 2023-08-04 jrmu (if (null? clauses)
322 665c255d 2023-08-04 jrmu 'false ; no else clause
323 665c255d 2023-08-04 jrmu (let ((first (car clauses))
324 665c255d 2023-08-04 jrmu (rest (cdr clauses)))
325 665c255d 2023-08-04 jrmu (if (cond-else-clause? first)
326 665c255d 2023-08-04 jrmu (if (null? rest)
327 665c255d 2023-08-04 jrmu (sequence->exp (cond-actions first))
328 665c255d 2023-08-04 jrmu (error "ELSE clause isn't last -- COND->IF"
330 665c255d 2023-08-04 jrmu (if (cond-extended-clause? first)
331 665c255d 2023-08-04 jrmu (make-if (cond-predicate first)
332 665c255d 2023-08-04 jrmu (make-application
333 665c255d 2023-08-04 jrmu (cond-extended-proc first)
334 665c255d 2023-08-04 jrmu (list (cond-predicate first)))
335 665c255d 2023-08-04 jrmu (expand-clauses rest))
336 665c255d 2023-08-04 jrmu (make-if (cond-predicate first)
337 665c255d 2023-08-04 jrmu (sequence->exp (cond-actions first))
338 665c255d 2023-08-04 jrmu (expand-clauses rest)))))))
339 665c255d 2023-08-04 jrmu (define (true? x)
340 665c255d 2023-08-04 jrmu (not (eq? x false)))
341 665c255d 2023-08-04 jrmu (define (false? x)
342 665c255d 2023-08-04 jrmu (eq? x false))
344 665c255d 2023-08-04 jrmu ;; procedure
345 665c255d 2023-08-04 jrmu (define (make-procedure parameters body env)
346 665c255d 2023-08-04 jrmu (list 'procedure parameters (scan-out-defines body) env))
347 665c255d 2023-08-04 jrmu (define (scan-out-defines body)
348 665c255d 2023-08-04 jrmu (let* ((definitions (filter definition? body))
349 665c255d 2023-08-04 jrmu (vars (map definition-variable definitions))
350 665c255d 2023-08-04 jrmu (unassigneds (map (lambda (var) ''*unassigned*)
352 665c255d 2023-08-04 jrmu (vals (map definition-value definitions))
353 665c255d 2023-08-04 jrmu (assignments
354 665c255d 2023-08-04 jrmu (map (lambda (var val)
355 665c255d 2023-08-04 jrmu (make-assignment var val))
356 665c255d 2023-08-04 jrmu vars vals))
357 665c255d 2023-08-04 jrmu (exps (remove definition? body)))
358 665c255d 2023-08-04 jrmu (if (null? definitions)
361 665c255d 2023-08-04 jrmu (make-let vars
362 665c255d 2023-08-04 jrmu unassigneds
363 665c255d 2023-08-04 jrmu (append assignments exps))))))
364 665c255d 2023-08-04 jrmu (define (compound-procedure? p)
365 665c255d 2023-08-04 jrmu (tagged-list? p 'procedure))
366 665c255d 2023-08-04 jrmu (define (procedure-parameters p) (cadr p))
367 665c255d 2023-08-04 jrmu (define (procedure-body p) (caddr p))
368 665c255d 2023-08-04 jrmu (define (procedure-environment p) (cadddr p))
370 665c255d 2023-08-04 jrmu ;; environment
371 665c255d 2023-08-04 jrmu (define (enclosing-environment env) (cdr env))
372 665c255d 2023-08-04 jrmu (define (first-frame env) (car env))
373 665c255d 2023-08-04 jrmu (define the-empty-environment '())
374 665c255d 2023-08-04 jrmu (define (make-frame variables values)
375 665c255d 2023-08-04 jrmu (cons variables values))
376 665c255d 2023-08-04 jrmu (define (frame-variables frame) (car frame))
377 665c255d 2023-08-04 jrmu (define (frame-values frame) (cdr frame))
378 665c255d 2023-08-04 jrmu (define (add-binding-to-frame! var val frame)
379 665c255d 2023-08-04 jrmu (set-car! frame (cons var (car frame)))
380 665c255d 2023-08-04 jrmu (set-cdr! frame (cons val (cdr frame))))
381 665c255d 2023-08-04 jrmu (define (extend-environment vars vals base-env)
382 665c255d 2023-08-04 jrmu (if (= (length vars) (length vals))
383 665c255d 2023-08-04 jrmu (cons (make-frame vars vals) base-env)
384 665c255d 2023-08-04 jrmu (if (< (length vars) (length vals))
385 665c255d 2023-08-04 jrmu (error "Too many arguments supplied" vars vals)
386 665c255d 2023-08-04 jrmu (error "Too few arguments supplied" vars vals))))
387 665c255d 2023-08-04 jrmu (define (lookup-variable-value var env)
388 665c255d 2023-08-04 jrmu (define (env-loop env)
389 665c255d 2023-08-04 jrmu (define (scan vars vals)
390 665c255d 2023-08-04 jrmu (cond ((null? vars)
391 665c255d 2023-08-04 jrmu (env-loop (enclosing-environment env)))
392 665c255d 2023-08-04 jrmu ((eq? var (car vars))
393 665c255d 2023-08-04 jrmu (let ((val (car vals)))
394 665c255d 2023-08-04 jrmu (if (eq? val '*unassigned*)
395 665c255d 2023-08-04 jrmu (error "Var not yet defined -- LOOKUP-VARIABLE-VALUE" var)
397 665c255d 2023-08-04 jrmu (else (scan (cdr vars) (cdr vals)))))
398 665c255d 2023-08-04 jrmu (if (eq? env the-empty-environment)
399 665c255d 2023-08-04 jrmu (error "Unbound variable" var)
400 665c255d 2023-08-04 jrmu (let ((frame (first-frame env)))
401 665c255d 2023-08-04 jrmu (scan (frame-variables frame)
402 665c255d 2023-08-04 jrmu (frame-values frame)))))
403 665c255d 2023-08-04 jrmu (env-loop env))
404 665c255d 2023-08-04 jrmu (define (set-variable-value! var val env)
405 665c255d 2023-08-04 jrmu (define (env-loop env)
406 665c255d 2023-08-04 jrmu (define (scan vars vals)
407 665c255d 2023-08-04 jrmu (cond ((null? vars)
408 665c255d 2023-08-04 jrmu (env-loop (enclosing-environment env)))
409 665c255d 2023-08-04 jrmu ((eq? var (car vars))
410 665c255d 2023-08-04 jrmu (set-car! vals val))
411 665c255d 2023-08-04 jrmu (else (scan (cdr vars) (cdr vals)))))
412 665c255d 2023-08-04 jrmu (if (eq? env the-empty-environment)
413 665c255d 2023-08-04 jrmu (error "Unbound variable -- SET!" var)
414 665c255d 2023-08-04 jrmu (let ((frame (first-frame env)))
415 665c255d 2023-08-04 jrmu (scan (frame-variables frame)
416 665c255d 2023-08-04 jrmu (frame-values frame)))))
417 665c255d 2023-08-04 jrmu (env-loop env))
418 665c255d 2023-08-04 jrmu (define (define-variable! var val env)
419 665c255d 2023-08-04 jrmu (let ((frame (first-frame env)))
420 665c255d 2023-08-04 jrmu (define (scan vars vals)
421 665c255d 2023-08-04 jrmu (cond ((null? vars)
422 665c255d 2023-08-04 jrmu (add-binding-to-frame! var val frame))
423 665c255d 2023-08-04 jrmu ((eq? var (car vars))
424 665c255d 2023-08-04 jrmu (set-car! vals val))
425 665c255d 2023-08-04 jrmu (else (scan (cdr vars) (cdr vals)))))
426 665c255d 2023-08-04 jrmu (scan (frame-variables frame)
427 665c255d 2023-08-04 jrmu (frame-values frame))))
429 665c255d 2023-08-04 jrmu (define (remove-binding-from-frame! var frame)
430 665c255d 2023-08-04 jrmu (define (scan vars vals)
431 665c255d 2023-08-04 jrmu (cond ((null? (cdr vars))
432 665c255d 2023-08-04 jrmu (error "Binding not found -- REMOVE-BINDING-FROM-FRAME!" var))
433 665c255d 2023-08-04 jrmu ((eq? var (cadr vars))
434 665c255d 2023-08-04 jrmu (set-cdr! vars (cddr vars))
435 665c255d 2023-08-04 jrmu (set-cdr! vals (cddr vals)))
436 665c255d 2023-08-04 jrmu (else (scan (cdr vars) (cdr vals)))))
437 665c255d 2023-08-04 jrmu (let ((vars (frame-variables frame))
438 665c255d 2023-08-04 jrmu (vals (frame-values frame)))
439 665c255d 2023-08-04 jrmu (if (eq? var (car vars))
440 665c255d 2023-08-04 jrmu (begin (set-car! frame (cdr vars))
441 665c255d 2023-08-04 jrmu (set-cdr! frame (cdr vals)))
442 665c255d 2023-08-04 jrmu (scan vars vals))))
444 665c255d 2023-08-04 jrmu ;; primitives
445 665c255d 2023-08-04 jrmu (define (primitive-procedure? proc)
446 665c255d 2023-08-04 jrmu (tagged-list? proc 'primitive))
447 665c255d 2023-08-04 jrmu (define (primitive-implementation proc) (cadr proc))
448 665c255d 2023-08-04 jrmu (define primitive-procedures
449 665c255d 2023-08-04 jrmu (list (list 'car car)
450 665c255d 2023-08-04 jrmu (list 'cdr cdr)
451 665c255d 2023-08-04 jrmu (list 'caar caar)
452 665c255d 2023-08-04 jrmu (list 'cadr cadr)
453 665c255d 2023-08-04 jrmu (list 'cddr cddr)
454 665c255d 2023-08-04 jrmu (list 'cons cons)
455 665c255d 2023-08-04 jrmu (list 'null? null?)
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 '< <)
462 665c255d 2023-08-04 jrmu (list '> >)
463 665c255d 2023-08-04 jrmu (list '<= <=)
464 665c255d 2023-08-04 jrmu (list '>= >=)
465 665c255d 2023-08-04 jrmu (list 'remainder remainder)
466 665c255d 2023-08-04 jrmu (list 'eq? eq?)
467 665c255d 2023-08-04 jrmu (list 'equal? equal?)
468 665c255d 2023-08-04 jrmu (list 'display display)))
469 665c255d 2023-08-04 jrmu (define (primitive-procedure-names)
471 665c255d 2023-08-04 jrmu primitive-procedures))
472 665c255d 2023-08-04 jrmu (define (primitive-procedure-objects)
473 665c255d 2023-08-04 jrmu (map (lambda (proc) (list 'primitive (cadr proc)))
474 665c255d 2023-08-04 jrmu primitive-procedures))
475 665c255d 2023-08-04 jrmu (define (apply-primitive-procedure proc args)
476 665c255d 2023-08-04 jrmu (apply-in-underlying-scheme
477 665c255d 2023-08-04 jrmu (primitive-implementation proc) args))
479 665c255d 2023-08-04 jrmu ;; driver-loop
480 665c255d 2023-08-04 jrmu (define input-prompt ";;; M-Eval input:")
481 665c255d 2023-08-04 jrmu (define output-prompt ";;; M-Eval value:")
482 665c255d 2023-08-04 jrmu (define (driver-loop)
483 665c255d 2023-08-04 jrmu (prompt-for-input input-prompt)
484 665c255d 2023-08-04 jrmu (let ((input (read)))
485 665c255d 2023-08-04 jrmu (let ((output (eval input the-global-environment)))
486 665c255d 2023-08-04 jrmu (announce-output output-prompt)
487 665c255d 2023-08-04 jrmu (user-print output)))
488 665c255d 2023-08-04 jrmu (driver-loop))
489 665c255d 2023-08-04 jrmu (define (prompt-for-input string)
490 665c255d 2023-08-04 jrmu (newline) (newline) (display string) (newline))
492 665c255d 2023-08-04 jrmu (define (announce-output string)
493 665c255d 2023-08-04 jrmu (newline) (display string) (newline))
494 665c255d 2023-08-04 jrmu (define (user-print object)
495 665c255d 2023-08-04 jrmu (if (compound-procedure? object)
496 665c255d 2023-08-04 jrmu (display (list 'compound-procedure
497 665c255d 2023-08-04 jrmu (procedure-parameters object)
498 665c255d 2023-08-04 jrmu (procedure-body object)
499 665c255d 2023-08-04 jrmu '<procedure-env>))
500 665c255d 2023-08-04 jrmu (display object)))
501 665c255d 2023-08-04 jrmu (define (setup-environment)
502 665c255d 2023-08-04 jrmu (let ((initial-env
503 665c255d 2023-08-04 jrmu (extend-environment (primitive-procedure-names)
504 665c255d 2023-08-04 jrmu (primitive-procedure-objects)
505 665c255d 2023-08-04 jrmu the-empty-environment)))
506 665c255d 2023-08-04 jrmu (define-variable! 'true true initial-env)
507 665c255d 2023-08-04 jrmu (define-variable! 'false false initial-env)
508 665c255d 2023-08-04 jrmu initial-env))
509 665c255d 2023-08-04 jrmu (define the-global-environment (setup-environment))
511 665c255d 2023-08-04 jrmu ;; auxiliary
512 665c255d 2023-08-04 jrmu (define (test-case actual expected)
514 665c255d 2023-08-04 jrmu (display "Actual: ")
515 665c255d 2023-08-04 jrmu (display actual)
517 665c255d 2023-08-04 jrmu (display "Expected: ")
518 665c255d 2023-08-04 jrmu (display expected)
520 665c255d 2023-08-04 jrmu (define (geval exp) ;; eval globally
521 665c255d 2023-08-04 jrmu (eval exp the-global-environment))
522 665c255d 2023-08-04 jrmu (define (test-eval exp expected)
523 665c255d 2023-08-04 jrmu (test-case (geval exp) expected))
527 665c255d 2023-08-04 jrmu ;; test-suite
529 665c255d 2023-08-04 jrmu ;; procedure definitions
532 665c255d 2023-08-04 jrmu '(define (assoc key records)
533 665c255d 2023-08-04 jrmu (cond ((null? records) false)
534 665c255d 2023-08-04 jrmu ((equal? key (caar records)) (car records))
535 665c255d 2023-08-04 jrmu (else (assoc key (cdr records))))))
538 665c255d 2023-08-04 jrmu '(define (map proc list)
539 665c255d 2023-08-04 jrmu (if (null? list)
541 665c255d 2023-08-04 jrmu (cons (proc (car list))
542 665c255d 2023-08-04 jrmu (map proc (cdr list))))))
545 665c255d 2023-08-04 jrmu '(define (accumulate op initial sequence)
546 665c255d 2023-08-04 jrmu (if (null? sequence)
548 665c255d 2023-08-04 jrmu (op (car sequence)
549 665c255d 2023-08-04 jrmu (accumulate op initial (cdr sequence))))))
551 665c255d 2023-08-04 jrmu ;; all special forms
552 665c255d 2023-08-04 jrmu (test-eval '(begin 5 6) 6)
553 665c255d 2023-08-04 jrmu (test-eval '10 10)
554 665c255d 2023-08-04 jrmu (geval '(define x 3))
555 665c255d 2023-08-04 jrmu (test-eval 'x 3)
556 665c255d 2023-08-04 jrmu (test-eval '(set! x -25) 'ok)
557 665c255d 2023-08-04 jrmu (test-eval 'x -25)
558 665c255d 2023-08-04 jrmu (geval '(define z (lambda (x y) (+ x (* x y)))))
559 665c255d 2023-08-04 jrmu (test-eval '(z 3 4) 15)
560 665c255d 2023-08-04 jrmu (test-eval '(cond ((= x -2) 'x=-2)
561 665c255d 2023-08-04 jrmu ((= x -25) 'x=-25)
562 665c255d 2023-08-04 jrmu (else 'failed))
564 665c255d 2023-08-04 jrmu (test-eval '(if true false true) false)
566 665c255d 2023-08-04 jrmu '(let ((x 4) (y 7))
567 665c255d 2023-08-04 jrmu (+ x y (* x y)))
568 665c255d 2023-08-04 jrmu (+ 4 7 (* 4 7)))
572 665c255d 2023-08-04 jrmu (geval '(define x (+ 3 8)))
573 665c255d 2023-08-04 jrmu (test-eval '(and 0 true x) 11)
574 665c255d 2023-08-04 jrmu (test-eval '(and 0 true x false) false)
575 665c255d 2023-08-04 jrmu (test-eval '(and 0 true x (set! x -2) false) false)
576 665c255d 2023-08-04 jrmu (test-eval 'x -2)
577 665c255d 2023-08-04 jrmu (test-eval '(and 0 true x false (set! x -5)) false)
578 665c255d 2023-08-04 jrmu (test-eval 'x -2)
579 665c255d 2023-08-04 jrmu (test-eval '(or false (set! x 25)) 'ok)
580 665c255d 2023-08-04 jrmu (test-eval 'x 25)
581 665c255d 2023-08-04 jrmu (test-eval '(or (set! x 2) (set! x 4)) 'ok)
582 665c255d 2023-08-04 jrmu (test-eval 'x 2)
583 665c255d 2023-08-04 jrmu (test-eval '(or false (set! x 25) true false) 'ok)
584 665c255d 2023-08-04 jrmu (test-eval 'x 25)
585 665c255d 2023-08-04 jrmu (test-eval '(or ((lambda (x) x) 5)) 5)
586 665c255d 2023-08-04 jrmu (test-eval '(or (begin (set! x (+ x 1)) x)) 26)
592 665c255d 2023-08-04 jrmu '(cond ((assoc 'b '((a 1) (b 2))) => cadr)
593 665c255d 2023-08-04 jrmu (else false))
597 665c255d 2023-08-04 jrmu '(cond ((= 3 4) 'not-true)
598 665c255d 2023-08-04 jrmu ((= (* 2 4) 3) 'also-false)
599 665c255d 2023-08-04 jrmu ((map (lambda (x)
600 665c255d 2023-08-04 jrmu (* x (+ x 1)))
601 665c255d 2023-08-04 jrmu '(2 4 1 9))
603 665c255d 2023-08-04 jrmu (lambda (x)
604 665c255d 2023-08-04 jrmu (accumulate + 0 x)))
605 665c255d 2023-08-04 jrmu (else 'never-reach))
607 665c255d 2023-08-04 jrmu ;; '(6 20 2 90)
610 665c255d 2023-08-04 jrmu ;; procedure definition and application
612 665c255d 2023-08-04 jrmu '(define (factorial n)
613 665c255d 2023-08-04 jrmu (if (= n 0)
615 665c255d 2023-08-04 jrmu (* n (factorial (- n 1))))))
616 665c255d 2023-08-04 jrmu (test-eval '(factorial 5) 120)
621 665c255d 2023-08-04 jrmu '(map (lambda (x)
622 665c255d 2023-08-04 jrmu (* x (+ x 1)))
623 665c255d 2023-08-04 jrmu '(2 1 4 2 8 3))
624 665c255d 2023-08-04 jrmu '(6 2 20 6 72 12))
625 665c255d 2023-08-04 jrmu ;; accumulate
628 665c255d 2023-08-04 jrmu '(accumulate + 0 '(1 2 3 4 5))
631 665c255d 2023-08-04 jrmu ;; make-let
633 665c255d 2023-08-04 jrmu (make-let '(x y) '(3 5) '((+ x y)))
640 665c255d 2023-08-04 jrmu '(let ((x 3))
644 665c255d 2023-08-04 jrmu '(let ((x 3)
649 665c255d 2023-08-04 jrmu '(let ((x 3)
651 665c255d 2023-08-04 jrmu (+ (let ((x (+ y 2))
655 665c255d 2023-08-04 jrmu (+ (* 4 3) 3 2))
657 665c255d 2023-08-04 jrmu '(let ((x 6)
658 665c255d 2023-08-04 jrmu (y (let ((x 2))
660 665c255d 2023-08-04 jrmu (z (let ((a (* 3 2)))
669 665c255d 2023-08-04 jrmu '(let* ((x 3)
670 665c255d 2023-08-04 jrmu (y (+ x 2))
671 665c255d 2023-08-04 jrmu (z (+ x y 5)))
680 665c255d 2023-08-04 jrmu '(let* ((x 3))
681 665c255d 2023-08-04 jrmu (let* ((y 5))
686 665c255d 2023-08-04 jrmu '(let* ((x 3)
687 665c255d 2023-08-04 jrmu (y (+ x 1)))
688 665c255d 2023-08-04 jrmu (+ (let* ((x (+ y 2))
692 665c255d 2023-08-04 jrmu (+ (* 6 6) 3 4))
694 665c255d 2023-08-04 jrmu '(let* ((x 6)
695 665c255d 2023-08-04 jrmu (y (let* ((x 2)
696 665c255d 2023-08-04 jrmu (a (let* ((x (* 3 x)))
699 665c255d 2023-08-04 jrmu (z (+ x y)))
703 665c255d 2023-08-04 jrmu ;; named-let
706 665c255d 2023-08-04 jrmu '(let eight ()
712 665c255d 2023-08-04 jrmu '(let loop ((count 0))
713 665c255d 2023-08-04 jrmu (if (= 100 count)
715 665c255d 2023-08-04 jrmu (loop (+ count 1))))
718 665c255d 2023-08-04 jrmu '(define (prime? x)
719 665c255d 2023-08-04 jrmu (let prime-iter ((i 2))
720 665c255d 2023-08-04 jrmu (cond ((> (* i i) x) true)
721 665c255d 2023-08-04 jrmu ((= (remainder x i) 0) false)
722 665c255d 2023-08-04 jrmu (else (prime-iter (+ i 1)))))))
724 665c255d 2023-08-04 jrmu '(let primes ((x 2)
726 665c255d 2023-08-04 jrmu (cond ((= n 0) '())
727 665c255d 2023-08-04 jrmu ((prime? x)
729 665c255d 2023-08-04 jrmu (primes (+ x 1) (- n 1))))
730 665c255d 2023-08-04 jrmu (else (primes (+ x 1) n))))
731 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))
734 665c255d 2023-08-04 jrmu '(define (fib n)
735 665c255d 2023-08-04 jrmu (let fib-iter ((a 1)
738 665c255d 2023-08-04 jrmu (if (= count 0)
740 665c255d 2023-08-04 jrmu (fib-iter (+ a b) a (- count 1))))))
741 665c255d 2023-08-04 jrmu (test-eval '(fib 19) 4181)
745 665c255d 2023-08-04 jrmu '(let ((y 0))
746 665c255d 2023-08-04 jrmu (do ((x 0 (+ x 1)))
747 665c255d 2023-08-04 jrmu ((= x 5) y)
748 665c255d 2023-08-04 jrmu (set! y (+ y 1))))
759 665c255d 2023-08-04 jrmu '(let ((y 0))
761 665c255d 2023-08-04 jrmu ((= y 5) y)
762 665c255d 2023-08-04 jrmu (set! y (+ y 1))))
766 665c255d 2023-08-04 jrmu '(do ((y '(1 2 3 4)))
767 665c255d 2023-08-04 jrmu ((null? y))
768 665c255d 2023-08-04 jrmu (set! y (cdr y)))
771 665c255d 2023-08-04 jrmu '(let ((y 0))
772 665c255d 2023-08-04 jrmu (do ((x 0 (+ x 1)))
773 665c255d 2023-08-04 jrmu ((= x 5) y)
774 665c255d 2023-08-04 jrmu (set! y (+ y 1))))
777 665c255d 2023-08-04 jrmu '(let ((x '(1 3 5 7 9)))
778 665c255d 2023-08-04 jrmu (do ((x x (cdr x))
779 665c255d 2023-08-04 jrmu (sum 0 (+ sum (car x))))
780 665c255d 2023-08-04 jrmu ((null? x) sum)))
783 665c255d 2023-08-04 jrmu '(let ((z '()))
784 665c255d 2023-08-04 jrmu (do ((x '(1 2 3 4) (cdr x))
785 665c255d 2023-08-04 jrmu (y '(1 2 3 4 5 6 7 8) (cddr y)))
786 665c255d 2023-08-04 jrmu ((null? x) y x z)
787 665c255d 2023-08-04 jrmu (set! z (cons (car x) z))))
788 665c255d 2023-08-04 jrmu '(4 3 2 1))
792 665c255d 2023-08-04 jrmu ;; make-unbound!
793 665c255d 2023-08-04 jrmu ;; broken now due to scan-out-defines
795 665c255d 2023-08-04 jrmu ;; (test-eval
796 665c255d 2023-08-04 jrmu ;; '(let ((x 3))
797 665c255d 2023-08-04 jrmu ;; (let ((x 5))
798 665c255d 2023-08-04 jrmu ;; (make-unbound! x)
799 665c255d 2023-08-04 jrmu ;; (* x x)))
802 665c255d 2023-08-04 jrmu ;; (test-eval
803 665c255d 2023-08-04 jrmu ;; '(let ((x 3))
804 665c255d 2023-08-04 jrmu ;; (let ((x 5))
805 665c255d 2023-08-04 jrmu ;; (define y x)
806 665c255d 2023-08-04 jrmu ;; (make-unbound! x)
807 665c255d 2023-08-04 jrmu ;; (* y x)))
810 665c255d 2023-08-04 jrmu ;; (test-eval
811 665c255d 2023-08-04 jrmu ;; '(let ((y -1) (x 3))
812 665c255d 2023-08-04 jrmu ;; (let ((y 0.5) (x 5))
813 665c255d 2023-08-04 jrmu ;; (define a x)
814 665c255d 2023-08-04 jrmu ;; (define b y)
815 665c255d 2023-08-04 jrmu ;; (make-unbound! x)
816 665c255d 2023-08-04 jrmu ;; (make-unbound! y)
817 665c255d 2023-08-04 jrmu ;; (* a b x y)))
818 665c255d 2023-08-04 jrmu ;; (* 5 3 -1 0.5))
820 665c255d 2023-08-04 jrmu ;; (test-eval
821 665c255d 2023-08-04 jrmu ;; '(let ((x 3) (y 4))
822 665c255d 2023-08-04 jrmu ;; (let ((x 5))
823 665c255d 2023-08-04 jrmu ;; (make-unbound! x)
824 665c255d 2023-08-04 jrmu ;; (+ x 4)))
827 665c255d 2023-08-04 jrmu ;; (test-eval
828 665c255d 2023-08-04 jrmu ;; '(let ((a 1) (b 2) (c 3) (d 4))
829 665c255d 2023-08-04 jrmu ;; (make-unbound! b)
830 665c255d 2023-08-04 jrmu ;; (+ a c d))
831 665c255d 2023-08-04 jrmu ;; (+ 1 3 4))
833 665c255d 2023-08-04 jrmu ;; (test-eval
834 665c255d 2023-08-04 jrmu ;; '(let ((x 4) (y 5))
835 665c255d 2023-08-04 jrmu ;; (let ((a 1) (b 2) (c 3))
836 665c255d 2023-08-04 jrmu ;; (let ((x (+ a b)) (y (+ c a)))
837 665c255d 2023-08-04 jrmu ;; (make-unbound! x)
838 665c255d 2023-08-04 jrmu ;; (let ((a x) (b (+ x y)))
839 665c255d 2023-08-04 jrmu ;; (define z b)
840 665c255d 2023-08-04 jrmu ;; (make-unbound! b)
841 665c255d 2023-08-04 jrmu ;; (* (+ a z)
842 665c255d 2023-08-04 jrmu ;; (+ a b y))))))
843 665c255d 2023-08-04 jrmu ;; (* (+ 4 8)
844 665c255d 2023-08-04 jrmu ;; (+ 4 2 4)))
846 665c255d 2023-08-04 jrmu ;; x 3 -- y 4
847 665c255d 2023-08-04 jrmu ;; x 4 -- y 4
848 665c255d 2023-08-04 jrmu ;; a 4 -- b 4
849 665c255d 2023-08-04 jrmu ;; a 4 -- b 2
851 665c255d 2023-08-04 jrmu ;; scan-out-defines
854 665c255d 2023-08-04 jrmu '(define (f x)
855 665c255d 2023-08-04 jrmu (define (even? n)
856 665c255d 2023-08-04 jrmu (if (= n 0)
858 665c255d 2023-08-04 jrmu (odd? (- n 1))))
859 665c255d 2023-08-04 jrmu (define (odd? n)
860 665c255d 2023-08-04 jrmu (if (= n 0)
862 665c255d 2023-08-04 jrmu (even? (- n 1))))
863 665c255d 2023-08-04 jrmu (even? x)))
864 665c255d 2023-08-04 jrmu (test-eval '(f 5) false)
865 665c255d 2023-08-04 jrmu (test-eval '(f 10) true)
868 665c255d 2023-08-04 jrmu ;; '(let ((x 5))
869 665c255d 2023-08-04 jrmu ;; (define y x)
870 665c255d 2023-08-04 jrmu ;; (define x 3)
871 665c255d 2023-08-04 jrmu ;; (+ x y)))
872 665c255d 2023-08-04 jrmu ;; signal an error because x is undefined if variables are scanned out
877 665c255d 2023-08-04 jrmu '(define (f x)
878 665c255d 2023-08-04 jrmu (letrec ((even?
879 665c255d 2023-08-04 jrmu (lambda (n)
880 665c255d 2023-08-04 jrmu (if (= n 0)
882 665c255d 2023-08-04 jrmu (odd? (- n 1)))))
884 665c255d 2023-08-04 jrmu (lambda (n)
885 665c255d 2023-08-04 jrmu (if (= n 0)
887 665c255d 2023-08-04 jrmu (even? (- n 1))))))
888 665c255d 2023-08-04 jrmu (even? x))))
889 665c255d 2023-08-04 jrmu (test-eval '(f 11) false)
890 665c255d 2023-08-04 jrmu (test-eval '(f 16) true)
893 665c255d 2023-08-04 jrmu '(letrec ((fact
894 665c255d 2023-08-04 jrmu (lambda (n)
895 665c255d 2023-08-04 jrmu (if (= n 1)
897 665c255d 2023-08-04 jrmu (* n (fact (- n 1)))))))
