1 ;; (define apply-in-underlying-scheme apply)
2 
3 (define (eval exp env)
4   (cond ((self-evaluating? exp) exp)
5         ((variable? exp) (lookup-variable-value exp env))
6         ((quoted? exp) (text-of-quotation exp))
7 	((quoted-list? exp) (eval (list->cons (text-of-quotation exp)) env))
8         ((assignment? exp) (eval-assignment exp env))
9         ((definition? exp) (eval-definition exp env))
10 ;;	((unbound? exp) (eval-unbound exp env))
11         ((if? exp) (eval-if exp env))
12 	((and? exp) (eval-and exp env))
13 	((or? exp) (eval-or exp env))
14         ((lambda? exp)
15          (make-procedure (lambda-parameters exp)
16                          (lambda-body exp)
17                          env))
18         ((begin? exp) 
19          (eval-sequence (begin-actions exp) env))
20         ((cond? exp) (eval (cond->if exp) env))
21 	((let? exp) (eval (let->combination exp) env))
22 	((let*? exp) (eval (let*->nested-lets exp) env))
23 	((named-let? exp) (eval (named-let->combination exp) env))
24 	((letrec? exp) (eval (letrec->let exp) env))
25 	((do? exp) (eval (do->combination exp) env))
26         ((application? exp)
27          (apply (actual-value (operator exp) env)
28                 (operands exp)
29 		env))
30         (else
31          (error "Unknown expression type -- EVAL" exp))))
32 (define (apply procedure arguments env)
33   (cond ((primitive-procedure? procedure)
34          (apply-primitive-procedure 
35 	  procedure 
36 	  (list-of-arg-values arguments env)))
37         ((compound-procedure? procedure)
38          (eval-sequence
39            (procedure-body procedure)
40            (extend-environment
41              (procedure-parameters procedure)
42              (list-of-delayed-args arguments env)
43              (procedure-environment procedure))))
44         (else
45          (error
46           "Unknown procedure type -- APPLY" procedure))))
47 
48 (define (thunk? obj)
49   (tagged-list? obj 'thunk))
50 (define (thunk-exp thunk)
51   (cadr thunk))
52 (define (thunk-env thunk)
53   (caddr thunk))
54 (define (evaluated-thunk? obj)
55   (tagged-list? obj 'evaluated-thunk))
56 (define (thunk-value evaluated-thunk)
57   (cadr evaluated-thunk))
58 (define (delay-it exp env)
59   `(thunk ,exp ,env))
60 (define (actual-value exp env)
61   (force-it (eval exp env)))
62 (define (force-it obj)
63   (cond ((thunk? obj)
64 	 (let ((result (actual-value 
65 			(thunk-exp obj)
66 			(thunk-env obj))))
67 	   (set-car! obj 'evaluated-thunk)
68 	   (set-car! (cdr obj) result)
69 	   (set-cdr! (cdr obj) '())
70 	   result))
71 	((evaluated-thunk? obj)
72 	 (thunk-value obj))
73 	(else obj)))
74 
75 (define (list-of-arg-values exps env)
76   (if (no-operands? exps)
77       '()
78       (cons (actual-value (first-operand exps) env)
79             (list-of-arg-values (rest-operands exps) env))))
80 (define (list-of-delayed-args exps env)
81   (if (no-operands? exps)
82       '()
83       (cons (delay-it (first-operand exps) env)
84 	    (list-of-delayed-args (rest-operands exps) env))))
85 
86 (define (tagged-list? exp tag)
87   (if (pair? exp)
88       (eq? (car exp) tag)
89       false))
90 
91 ;; self-evaluating/variable/quoted
92 (define (self-evaluating? exp)
93   (cond ((number? exp) true)
94         ((string? exp) true)
95         (else false)))
96 (define (variable? exp) (symbol? exp))
97 (define (quoted? exp)
98   (and (tagged-list? exp 'quote)
99        (not (pair? (cadr exp)))))
100 (define (text-of-quotation exp) (cadr exp))
101 (define (quoted-list? exp)
102   (and (tagged-list? exp 'quote)
103        (pair? (cadr exp))))
104 (define (list->cons exp)
105   (if (pair? exp)
106       (make-cons (list->cons (car exp))
107 		 (list->cons (cdr exp)))
108       (make-quote exp)))
109 (define (make-quote exp)
110   `(quote ,exp))
111 (define (make-cons x y)
112   `(cons ,x ,y))
113 
114 
115 ;; assignment/definition
116 (define (assignment? exp)
117   (tagged-list? exp 'set!))
118 (define (assignment-variable exp) (cadr exp))
119 (define (assignment-value exp) (caddr exp))
120 (define (make-assignment var val)
121   (list 'set! var val))
122 (define (definition? exp)
123   (tagged-list? exp 'define))
124 (define (definition-variable exp)
125   (if (symbol? (cadr exp))
126       (cadr exp)
127       (caadr exp)))
128 (define (definition-value exp)
129   (if (symbol? (cadr exp))
130       (caddr exp)
131       (make-lambda (cdadr exp)   ; formal parameters
132                    (cddr exp)))) ; body
133 (define (eval-assignment exp env)
134   (set-variable-value! (assignment-variable exp)
135                        (eval (assignment-value exp) env)
136                        env)
137   'ok)
138 (define (eval-definition exp env)
139   (define-variable! (definition-variable exp)
140                     (eval (definition-value exp) env)
141                     env)
142   'ok)
143 (define (make-definition var val)
144   `(define ,var ,val))
145 
146 ;; make-unbound!
147 
148 ;; (define (unbound? exp)
149 ;;   (tagged-list? exp 'make-unbound!))
150 ;; (define (unbound-var exp)
151 ;;   (cadr exp))
152 ;; (define (eval-unbound exp env)
153 ;;   (remove-binding-from-frame! (unbound-var exp) (first-frame env)))
154 
155 
156 
157 ;; if/and/or
158 (define (if? exp) (tagged-list? exp 'if))
159 (define (if-predicate exp) (cadr exp))
160 (define (if-consequent exp) (caddr exp))
161 (define (if-alternative exp)
162   (if (not (null? (cdddr exp)))
163       (cadddr exp)
164       'false))
165 (define (make-if predicate consequent alternative)
166   (list 'if predicate consequent alternative))
167 (define (eval-if exp env)
168   (if (true? (actual-value (if-predicate exp) env))
169       (eval (if-consequent exp) env)
170       (eval (if-alternative exp) env)))
171 
172 (define (and? exp)
173   (tagged-list? exp 'and))
174 (define (and-clauses exp)
175   (cdr exp))
176 (define (or? exp)
177   (tagged-list? exp 'or))
178 (define (or-clauses exp)
179   (cdr exp))
180 (define (eval-and exp env)
181   (define (eval-clauses clauses)
182     (cond ((null? clauses) true)
183 	  ((null? (cdr clauses)) (eval (car clauses) env))
184 	  (else (and (eval (car clauses) env)
185 		     (eval-clauses (cdr clauses))))))
186   (eval-clauses (and-clauses exp)))
187 (define (eval-or exp env)
188   (define (eval-clauses clauses)
189     (if (null? clauses)
190 	false
191 	(or (eval (car clauses) env)
192 	    (eval-clauses (cdr clauses)))))
193   (eval-clauses (or-clauses exp)))
194 
195 
196 ;; lambda/let/let*/letrec
197 (define (lambda? exp) (tagged-list? exp 'lambda))
198 (define (lambda-parameters exp) (cadr exp))
199 (define (lambda-body exp) (cddr exp))
200 (define (make-lambda parameters body)
201   (cons 'lambda (cons parameters body)))
202 
203 (define (make-let vars vals body)
204   (cons 'let
205 	(cons (map list vars vals)
206 	      body)))
207 (define (let? exp)
208   (and (tagged-list? exp 'let)
209        (not (symbol? (cadr exp)))))
210 (define (let-vars exp)
211   (map car (cadr exp)))
212 (define (let-vals exp)
213   (map cadr (cadr exp)))
214 (define (let-body exp)
215   (cddr exp))
216 (define (let->combination exp)
217   (make-application (make-lambda (let-vars exp) (let-body exp))
218 		    (let-vals exp)))
219 (define (named-let? exp)
220   (and (tagged-list? exp 'let)
221        (symbol? (cadr exp))))
222 (define (named-let-name exp)
223   (cadr exp))
224 (define (named-let-vars exp)
225   (map car (caddr exp)))
226 (define (named-let-vals exp)
227   (map cadr (caddr exp)))
228 (define (named-let-body exp)
229   (cdddr exp))
230 (define (named-let->combination exp)
231   (sequence->exp
232    (list (make-definition (named-let-name exp)
233 			  (make-lambda (named-let-vars exp)
234 				       (named-let-body exp)))
235 	 (make-application (named-let-name exp)
236 			   (named-let-vals exp)))))
237 (define (make-named-let name vars vals body)
238   (cons 'let 
239 	(cons name
240 	      (cons (map list vars vals)
241 		    body))))
242 
243 (define (letrec? exp)
244   (tagged-list? exp 'letrec))
245 
246 (define (letrec-vars exp)
247   (map car (cadr exp)))
248 (define (letrec-vals exp)
249   (map cadr (cadr exp)))
250 (define (letrec-body exp)
251   (cddr exp))
252 (define (letrec->let exp)
253   (let* ((vars (letrec-vars exp))
254 	 (unassigneds (map (lambda (var) ''*unassigned*)
255 			   vars))
256 	 (vals (letrec-vals exp))
257 	 (assignments (map (lambda (var val)
258 			     (make-assignment var val))
259 			   vars
260 			   vals))
261 	 (body (letrec-body exp)))
262   (make-let vars 
263 	    unassigneds
264 	    (append assignments body))))
265 
266 
267 
268 
269 (define (let*? exp)
270   (tagged-list? exp 'let*))
271 (define let*-vars let-vars)
272 (define let*-vals let-vals)
273 (define let*-body let-body)
274 (define (let*->nested-lets exp)
275   (define (expand-lets vars vals)
276     (if (null? (cdr vars))
277 	(make-let (list (car vars)) 
278 		  (list (car vals))
279 		  (let*-body exp))
280 	(make-let (list (car vars))
281 		  (list (car vals))
282 		  (list (expand-lets (cdr vars) (cdr vals))))))
283   (let ((vars (let*-vars exp))
284 	(vals (let*-vals exp)))
285     (if (null? vars)
286 	(sequence->exp (let*-body exp))
287 	(expand-lets vars vals))))
288 
289 ;; do loop
290 (define (do? exp)
291   (tagged-list? exp 'do))
292 (define (do-vars exp)
293   (map car (cadr exp)))
294 (define (do-inits exp)
295   (map cadr (cadr exp)))
296 (define (do-steps exp)
297   (map (lambda (var-init-step)
298 	 (if (null? (cddr var-init-step))
299 	     (car var-init-step)
300 	     (caddr var-init-step)))
301        (cadr exp)))
302 (define (do-test exp)
303   (caaddr exp))
304 (define (do-expressions exp)
305   (if (null? (cdaddr exp))
306       (caddr exp)
307       (cdaddr exp)))
308 (define (do-commands exp)
309   (cdddr exp))
310 (define (do->combination exp)
311   (make-named-let
312    'do-iter
313    (do-vars exp)
314    (do-inits exp)
315    (list
316     (make-if
317      (do-test exp)
318      (sequence->exp (do-expressions exp))
319      (sequence->exp
320       (append (do-commands exp)
321 	      (list (make-application
322 		     'do-iter
323 		     (do-steps exp)))))))))
324 
325 
326 ;; begin/sequence
327 (define (begin? exp) (tagged-list? exp 'begin))
328 (define (begin-actions exp) (cdr exp))
329 (define (last-exp? seq) (null? (cdr seq)))
330 (define (first-exp seq) (car seq))
331 (define (rest-exps seq) (cdr seq))
332 (define (sequence->exp seq)
333   (cond ((null? seq) seq)
334         ((last-exp? seq) (first-exp seq))
335         (else (make-begin seq))))
336 (define (make-begin seq) (cons 'begin seq))
337 (define (eval-sequence exps env)
338   (cond ((last-exp? exps) (eval (first-exp exps) env))
339         (else (eval (first-exp exps) env)
340               (eval-sequence (rest-exps exps) env))))
341 
342 ;; application
343 (define (make-application op args)
344   (cons op args))
345 (define (application? exp) (pair? exp))
346 (define (operator exp) (car exp))
347 (define (operands exp) (cdr exp))
348 (define (no-operands? ops) (null? ops))
349 (define (first-operand ops) (car ops))
350 (define (rest-operands ops) (cdr ops))
351 
352 ;; cond
353 (define (cond? exp) (tagged-list? exp 'cond))
354 (define (cond-clauses exp) (cdr exp))
355 (define (cond-else-clause? clause)
356   (eq? (cond-predicate clause) 'else))
357 (define (cond-predicate clause) (car clause))
358 (define (cond-actions clause) (cdr clause))
359 (define (cond-extended-clause? clause)
360   (and (not (null? (cdr clause))) (eq? (cadr clause) '=>)))
361 (define (cond-extended-proc clause)
362   (caddr clause))
363 (define (cond->if exp)
364   (expand-clauses (cond-clauses exp)))
365 (define (expand-clauses clauses)
366   (if (null? clauses)
367       'false                          ; no else clause
368       (let ((first (car clauses))
369             (rest (cdr clauses)))
370         (if (cond-else-clause? first)
371             (if (null? rest)
372                 (sequence->exp (cond-actions first))
373                 (error "ELSE clause isn't last -- COND->IF"
374                        clauses))
375 	    (if (cond-extended-clause? first)
376 		(make-if (cond-predicate first)
377 			 (make-application
378 			  (cond-extended-proc first)
379 			  (list (cond-predicate first)))
380 			 (expand-clauses rest))
381 		(make-if (cond-predicate first)
382 			 (sequence->exp (cond-actions first))
383 			 (expand-clauses rest)))))))
384 (define (true? x)
385   (not (eq? x false)))
386 (define (false? x)
387   (eq? x false))
388 
389 ;; procedure
390 (define (make-procedure parameters body env)
391   (list 'procedure parameters body env))
392 ;; (define (scan-out-defines body)
393 ;;   (let* ((definitions (filter definition? body))
394 ;; 	 (vars (map definition-variable definitions))
395 ;; 	 (unassigneds (map (lambda (var) ''*unassigned*) 
396 ;; 			   vars))
397 ;; 	 (vals (map definition-value definitions))
398 ;; 	 (assignments 
399 ;; 	  (map (lambda (var val)
400 ;; 		 (make-assignment var val))
401 ;; 	       vars vals))
402 ;; 	 (exps (remove definition? body)))
403 ;;     (if (null? definitions)
404 ;; 	body
405 ;; 	(list
406 ;; 	 (make-let vars
407 ;; 		   unassigneds
408 ;; 		   (append assignments exps))))))
409 (define (compound-procedure? p)
410   (tagged-list? p 'procedure))
411 (define (procedure-parameters p) (cadr p))
412 (define (procedure-body p) (caddr p))
413 (define (procedure-environment p) (cadddr p))
414 
415 ;; environment
416 (define (enclosing-environment env) (cdr env))
417 (define (first-frame env) (car env))
418 (define the-empty-environment '())
419 (define (make-frame variables values)
420   (cons variables values))
421 (define (frame-variables frame) (car frame))
422 (define (frame-values frame) (cdr frame))
423 (define (add-binding-to-frame! var val frame)
424   (set-car! frame (cons var (car frame)))
425   (set-cdr! frame (cons val (cdr frame))))
426 (define (extend-environment vars vals base-env)
427   (if (= (length vars) (length vals))
428       (cons (make-frame vars vals) base-env)
429       (if (< (length vars) (length vals))
430           (error "Too many arguments supplied" vars vals)
431           (error "Too few arguments supplied" vars vals))))
432 (define (lookup-variable-value var env)
433   (define (env-loop env)
434     (define (scan vars vals)
435       (cond ((null? vars)
436              (env-loop (enclosing-environment env)))
437             ((eq? var (car vars))
438 	     (let ((val (car vals)))
439 	       (if (eq? val '*unassigned*)
440 		   (error "Var not yet defined -- LOOKUP-VARIABLE-VALUE" var)
441 		   val)))
442             (else (scan (cdr vars) (cdr vals)))))
443     (if (eq? env the-empty-environment)
444         (error "Unbound variable" var)
445         (let ((frame (first-frame env)))
446           (scan (frame-variables frame)
447                 (frame-values frame)))))
448   (env-loop env))
449 (define (set-variable-value! var val env)
450   (define (env-loop env)
451     (define (scan vars vals)
452       (cond ((null? vars)
453              (env-loop (enclosing-environment env)))
454             ((eq? var (car vars))
455              (set-car! vals val))
456             (else (scan (cdr vars) (cdr vals)))))
457     (if (eq? env the-empty-environment)
458         (error "Unbound variable -- SET!" var)
459         (let ((frame (first-frame env)))
460           (scan (frame-variables frame)
461                 (frame-values frame)))))
462   (env-loop env))
463 (define (define-variable! var val env)
464   (let ((frame (first-frame env)))
465     (define (scan vars vals)
466       (cond ((null? vars)
467              (add-binding-to-frame! var val frame))
468             ((eq? var (car vars))
469              (set-car! vals val))
470             (else (scan (cdr vars) (cdr vals)))))
471     (scan (frame-variables frame)
472           (frame-values frame))))
473 
474 (define (remove-binding-from-frame! var frame)
475   (define (scan vars vals)
476     (cond ((null? (cdr vars))
477 	   (error "Binding not found -- REMOVE-BINDING-FROM-FRAME!" var))
478 	  ((eq? var (cadr vars))
479 	   (set-cdr! vars (cddr vars))
480 	   (set-cdr! vals (cddr vals)))
481 	  (else (scan (cdr vars) (cdr vals)))))
482   (let ((vars (frame-variables frame))
483 	(vals (frame-values frame)))
484     (if (eq? var (car vars))
485 	(begin (set-car! frame (cdr vars))
486 	       (set-cdr! frame (cdr vals)))
487 	(scan vars vals))))
488 
489 ;; primitives
490 (define (primitive-procedure? proc)
491   (tagged-list? proc 'primitive))
492 (define (primitive-implementation proc) (cadr proc))
493 (define primitive-procedures
494   (list (list 'car car)
495         (list 'cdr cdr)
496 	(list 'caar caar)
497 	(list 'cadr cadr)
498 	(list 'cddr cddr)
499         (list 'cons cons)
500         (list 'null? null?)
501 	(list '* *)
502 	(list '/ /)
503 	(list '+ +)
504 	(list '- -)
505 	(list '= =)
506 	(list '< <)
507 	(list '> >)
508 	(list '<= <=)
509 	(list '>= >=)
510 	(list 'remainder remainder)
511 	(list 'eq? eq?)
512 	(list 'equal? equal?)
513 	(list 'display display)))
514 (define (primitive-procedure-names)
515   (map car
516        primitive-procedures))
517 (define (primitive-procedure-objects)
518   (map (lambda (proc) (list 'primitive (cadr proc)))
519        primitive-procedures))
520 (define (apply-primitive-procedure proc args)
521   (apply-in-underlying-scheme
522    (primitive-implementation proc) args))
523 
524 ;; driver-loop
525 (define input-prompt ";;; M-Eval input:")
526 (define output-prompt ";;; M-Eval value:")
527 (define (driver-loop)
528   (prompt-for-input input-prompt)
529   (let ((input (read)))
530     (let ((output (actual-value input the-global-environment)))
531       (announce-output output-prompt)
532       (user-print output)))
533   (driver-loop))
534 (define (prompt-for-input string)
535   (newline) (newline) (display string) (newline))
536 
537 (define (announce-output string)
538   (newline) (display string) (newline))
539 (define (user-print object)
540   (if (compound-procedure? object)
541       (display (list 'compound-procedure
542                      (procedure-parameters object)
543                      (procedure-body object)
544                      '<procedure-env>))
545       (display object)))
546 (define (setup-environment)
547   (let ((initial-env
548          (extend-environment (primitive-procedure-names)
549                              (primitive-procedure-objects)
550                              the-empty-environment)))
551     (define-variable! 'true true initial-env)
552     (define-variable! 'false false initial-env)
553     initial-env))
554 (define the-global-environment (setup-environment))
555 
556 ;; auxiliary
557 (define (test-case actual expected)
558   (newline)
559   (display "Actual:   ")
560   (display actual)
561   (newline)
562   (display "Expected: ")
563   (display expected)
564   (newline))
565 (define (geval exp) ;; eval globally
566   (eval exp the-global-environment))
567 (define (test-eval exp expected)
568   (test-case (force-it (geval exp)) expected))
569 
570 ;; cons/car/cdr
571 
572 (geval 
573  '(define (cons x y)
574     (lambda (m) (m x y))))
575 (geval
576  '(define (car z)
577     (z (lambda (p q) p))))
578 (geval
579  '(define (cdr z)
580     (z (lambda (p q) q))))
581 (geval
582  '(define (list-ref items n)
583     (if (= n 0)
584 	(car items)
585 	(list-ref (cdr items) (- n 1)))))
586 (geval
587  '(define (map proc items)
588     (if (null? items)
589 	'()
590 	(cons (proc (car items))
591 	      (map proc (cdr items))))))
592 (geval
593  '(define (scale-list items factor)
594     (map (lambda (x) (* x factor))
595 	 items)))
596 (geval
597  '(define (add-lists list1 list2)
598     (cond ((null? list1) list2)
599 	  ((null? list2) list1)
600 	  (else (cons (+ (car list1) (car list2))
601 		      (add-lists (cdr list1) (cdr list2)))))))
602 
603 
604 
605 
606 ;; Exercise 4.34.  Modify the driver loop for the evaluator so that lazy pairs and lists will print in some reasonable way. (What are you going to do about infinite lists?) You may also need to modify the representation of lazy pairs so that the evaluator can identify them in order to print them. 
607 
608 
609 (test-eval
610  '(car (cons (quote a) (quote ())))
611  'a)
612 (test-eval
613  '(cdr (cons (quote a) (quote ())))
614  '())
615 (test-eval
616  '(car '(a))
617  'a)
618 (test-eval
619  '(cdr '(a))
620  '())
621 (test-eval
622  '(car (cdr '(a b)))
623  'b)
624 (test-eval
625  '(car (car '((a b) c)))
626  'a)
627 (test-eval
628  '(car (cdr (car (cdr '((a c) (b d))))))
629  'd)
630 
631 
632 
633 
634 (geval 
635  '(define ones (cons 1 ones)))
636 (geval
637  '(define integers (cons 1 (add-lists ones integers))))
638 (test-eval 
639  '(list-ref integers 17)
640  18)
641 
642 (test-eval
643  '(car (cdr (add-lists '(1 2 3 4 5) '(2 3 4 5 6))))
644  5)
645 
646 (geval
647  '(define (integral integrand initial-value dt)
648     (define int
649       (cons initial-value
650 	    (add-lists (scale-list integrand dt)
651 		       int)))
652     int))
653 (geval
654  '(define (solve f y0 dt)
655     (define y (integral dy y0 dt))
656     (define dy (map f y))
657     y))
658 (test-eval 
659  '(list-ref (solve (lambda (x) x) 1 0.001) 1000)
660  2.716924)
661 
662 
663 ;; test-suite
664 
665 ;; procedure definitions
666 
667 (geval 
668  '(define (assoc key records)
669     (cond ((null? records) false)
670 	  ((equal? key (caar records)) (car records))
671 	  (else (assoc key (cdr records))))))
672 
673 (geval
674  '(define (map proc list)
675     (if (null? list)
676 	'()
677 	(cons (proc (car list))
678 	      (map proc (cdr list))))))
679 
680 (geval 
681  '(define (accumulate op initial sequence)
682     (if (null? sequence)
683 	initial
684 	(op (car sequence)
685 	    (accumulate op initial (cdr sequence))))))
686 
687 ;; all special forms
688 (test-eval '(begin 5 6) 6)
689 (test-eval '10 10)
690 (geval '(define x 3))
691 (test-eval 'x 3)
692 (test-eval '(set! x -25) 'ok)
693 (test-eval 'x -25)
694 (geval '(define z (lambda (x y) (+ x (* x y)))))
695 (test-eval '(z 3 4) 15)
696 (test-eval '(cond ((= x -2) 'x=-2)
697 		  ((= x -25) 'x=-25)
698 		  (else 'failed))
699 	   'x=-25)
700 (test-eval '(if true false true) false)
701 
702 (test-eval 
703  '(let ((x 4) (y 7))
704     (+ x y (* x y)))
705  (+ 4 7 (* 4 7)))
706 
707 
708 ;; and/or
709 (geval '(define x (+ 3 8)))
710 (test-eval '(and 0 true x) 11)
711 (test-eval '(and 0 true x false) false)
712 (test-eval '(and 0 true x (set! x -2) false) false)
713 (test-eval 'x -2)
714 (test-eval '(and 0 true x false (set! x -5)) false)
715 (test-eval 'x -2)
716 (test-eval '(or false (set! x 25)) 'ok)
717 (test-eval 'x 25)
718 (test-eval '(or (set! x 2) (set! x 4)) 'ok)
719 (test-eval 'x 2)
720 (test-eval '(or false (set! x 25) true false) 'ok)
721 (test-eval 'x 25)
722 (test-eval '(or ((lambda (x) x) 5)) 5)
723 (test-eval '(or (begin (set! x (+ x 1)) x)) 26)
724 
725 
726 ;; cond
727 
728 ;; (test-eval 
729 ;;  '(cond ((assoc 'b '((a 1) (b 2))) => cadr)
730 ;; 	(else false))
731 ;;  2)
732 
733 ;; (test-eval
734 ;;  '(cond ((= 3 4) 'not-true)
735 ;; 	((= (* 2 4) 3) 'also-false)
736 ;; 	((map (lambda (x)
737 ;; 		(* x (+ x 1)))
738 ;; 	      '(2 4 1 9))
739 ;; 	 =>
740 ;; 	 (lambda (x)
741 ;; 	   (accumulate + 0 x)))
742 ;; 	(else 'never-reach))
743 ;;  118)
744 ;; '(6 20 2 90)
745 
746 
747 ;; procedure definition and application
748 (geval
749  '(define (factorial n)
750     (if (= n 0)
751 	1
752 	(* n (factorial (- n 1))))))
753 (test-eval '(factorial 5) 120)
754 
755 ;; map
756 
757 ;; (test-eval
758 ;;  '(map (lambda (x)
759 ;; 	 (* x (+ x 1)))
760 ;;        '(2 1 4 2 8 3))
761 ;;  '(6 2 20 6 72 12))
762 ;; accumulate
763 
764 (test-eval
765  '(accumulate + 0 '(1 2 3 4 5))
766  15)
767 
768 ;; make-let
769 (test-eval 
770  (make-let '(x y) '(3 5) '((+ x y)))
771  8)
772 (test-eval 
773  '(let ()
774     5)
775  5)
776 (test-eval
777  '(let ((x 3))
778     x)
779  3)
780 (test-eval
781  '(let ((x 3)
782 	(y 5))
783     (+ x y))
784  8)
785 (test-eval 
786  '(let ((x 3)
787 	(y 2))
788     (+ (let ((x (+ y 2))
789 	     (y x))
790 	 (* x y))
791        x y))
792  (+ (* 4 3) 3 2))
793 (test-eval
794  '(let ((x 6)
795 	(y (let ((x 2))
796 	     (+ x 3)))
797 	(z (let ((a (* 3 2)))
798 	     (+ a 3))))
799     (+ x y z))
800  (+ 6 5 9))
801     
802 
803 ;; let*
804 
805 (test-eval
806  '(let* ((x 3)
807 	 (y (+ x 2))
808 	 (z (+ x y 5)))
809     (* x z))
810  39)
811 
812 (test-eval
813  '(let* ()
814     5)
815  5)
816 (test-eval
817  '(let* ((x 3))
818     (let* ((y 5))
819       (+ x y)))
820  8)
821 
822 (test-eval 
823  '(let* ((x 3)
824 	 (y (+ x 1)))
825     (+ (let* ((x (+ y 2))
826 	      (y x))
827 	 (* x y))
828        x y))
829  (+ (* 6 6) 3 4))
830 (test-eval
831  '(let* ((x 6)
832 	 (y (let* ((x 2)
833 		   (a (let* ((x (* 3 x)))
834 			(+ x 2))))       
835 	      (+ x a)))                  
836 	 (z (+ x y)))                    
837     (+ x y z))
838  32)
839 
840 ;; named-let
841 
842 (test-eval
843  '(let eight ()
844     5
845     7
846     8)
847  8)
848 (test-eval
849  '(let loop ((count 0))
850     (if (= 100 count)
851 	count
852 	(loop (+ count 1))))
853  100)
854 (geval
855  '(define (prime? x)
856     (let prime-iter ((i 2))
857       (cond ((> (* i i) x) true)
858 	    ((= (remainder x i) 0) false)
859 	    (else (prime-iter (+ i 1)))))))
860 ;; (test-eval
861 ;;  '(let primes ((x 2)
862 ;; 	       (n 20))
863 ;;     (cond ((= n 0) '())
864 ;; 	  ((prime? x) 
865 ;; 	   (cons x
866 ;; 		 (primes (+ x 1) (- n 1))))
867 ;; 	  (else (primes (+ x 1) n))))
868 ;;  '(2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71))
869 
870 (geval
871  '(define (fib n)
872     (let fib-iter ((a 1)
873 		   (b 0)
874 		   (count n))
875       (if (= count 0)
876 	  b
877 	  (fib-iter (+ a b) a (- count 1))))))
878 (test-eval '(fib 19) 4181)
879 
880 ;; do-loop	  
881 (test-eval
882  '(let ((y 0))
883     (do ((x 0 (+ x 1)))
884 	((= x 5) y)
885       (set! y (+ y 1))))
886  5)
887 (test-eval
888  '(do ()
889       (true))
890  true)
891 (test-eval
892  '(do ()
893       (true 5))
894  5)
895 (test-eval
896  '(let ((y 0))
897     (do ()
898 	((= y 5) y)
899       (set! y (+ y 1))))
900  5)
901 
902 (test-eval
903  '(do ((y '(1 2 3 4)))
904       ((null? y))
905     (set! y (cdr y)))
906  true)
907 (test-eval
908  '(let ((y 0))
909     (do ((x 0 (+ x 1)))
910 	((= x 5) y)
911       (set! y (+ y 1))))
912  5)
913 (test-eval
914  '(let ((x '(1 3 5 7 9)))
915     (do ((x x (cdr x))
916 	 (sum 0 (+ sum (car x))))
917 	((null? x) sum)))
918  25)
919 ;; (test-eval 
920 ;;  '(let ((z '()))
921 ;;     (do ((x '(1 2 3 4) (cdr x))
922 ;; 	 (y '(1 2 3 4 5 6 7 8) (cddr y)))
923 ;; 	((null? x) y x z)
924 ;;       (set! z (cons (car x) z))))
925 ;;  '(4 3 2 1))
926 
927 
928 
929 ;; make-unbound!
930 ;; broken now due to scan-out-defines
931 
932 ;; (test-eval
933 ;;  '(let ((x 3))
934 ;;     (let ((x 5))
935 ;;       (make-unbound! x)
936 ;;       (* x x)))
937 ;;  9)
938 
939 ;; (test-eval
940 ;;  '(let ((x 3))
941 ;;     (let ((x 5))
942 ;;       (define y x)
943 ;;       (make-unbound! x)
944 ;;       (* y x)))
945 ;;  15)
946 
947 ;; (test-eval
948 ;;  '(let ((y -1) (x 3))
949 ;;     (let ((y 0.5) (x 5))
950 ;;       (define a x)
951 ;;       (define b y)
952 ;;       (make-unbound! x)
953 ;;       (make-unbound! y)
954 ;;       (* a b x y)))
955 ;;  (* 5 3 -1 0.5))
956 
957 ;; (test-eval
958 ;;  '(let ((x 3) (y 4))
959 ;;     (let ((x 5))
960 ;;       (make-unbound! x)
961 ;;       (+ x 4)))
962 ;;  7)
963 
964 ;; (test-eval 
965 ;;  '(let ((a 1) (b 2) (c 3) (d 4))
966 ;;     (make-unbound! b)
967 ;;     (+ a c d))
968 ;;  (+ 1 3 4))
969 
970 ;; (test-eval
971 ;;  '(let ((x 4) (y 5))
972 ;;     (let ((a 1) (b 2) (c 3))
973 ;;       (let ((x (+ a b)) (y (+ c a)))
974 ;; 	(make-unbound! x)
975 ;; 	(let ((a x) (b (+ x y)))
976 ;; 	  (define z b)
977 ;; 	  (make-unbound! b)
978 ;; 	  (* (+ a z)
979 ;; 	     (+ a b y))))))
980 ;;  (* (+ 4 8)
981 ;;     (+ 4 2 4)))
982  
983 ;; x 3 -- y 4
984 ;; x 4 -- y 4
985 ;; a 4 -- b 4
986 ;; a 4 -- b 2
987 
988 ;; scan-out-defines
989 
990 (geval
991  '(define (f x)
992     (define (even? n)
993       (if (= n 0)
994 	  true
995 	  (odd? (- n 1))))
996     (define (odd? n)
997       (if (= n 0)
998 	  false
999 	  (even? (- n 1))))
1000     (even? x)))
1001 (test-eval '(f 5) false)
1002 (test-eval '(f 10) true)
1003 
1004 ;; (geval
1005 ;;  '(let ((x 5))
1006 ;;     (define y x)
1007 ;;     (define x 3)
1008 ;;     (+ x y)))
1009 ;; signal an error because x is undefined if variables are scanned out
1010 
1011 ;; letrec
1012 
1013 (geval
1014  '(define (f x)
1015     (letrec ((even?
1016 	      (lambda (n)
1017 		(if (= n 0)
1018 		    true
1019 		    (odd? (- n 1)))))
1020 	     (odd?
1021 	      (lambda (n)
1022 		(if (= n 0)
1023 		    false
1024 		    (even? (- n 1))))))
1025       (even? x))))
1026 (test-eval '(f 11) false)
1027 (test-eval '(f 16) true)
1028 
1029 (test-eval 
1030  '(letrec ((fact
1031 	    (lambda (n)
1032 	      (if (= n 1)
1033 		  1
1034 		  (* n (fact (- n 1)))))))
1035     (fact 10))
1036  3628800)
1037 
1038 
1039 ;; delayed-evaluation
1040 
1041 (geval
1042  '(define (try a b)
1043     (if (= a 0) 1 b)))
1044 (test-eval '(try 0 (/ 1 0)) 1)
1045 
1046 (geval 
1047  '(define (unless condition usual-value exceptional-value)
1048     (if condition exceptional-value usual-value)))
1049 (test-eval
1050  '(let ((a 4) (b 0))
1051     (unless (= b 0)
1052             (/ a b)
1053 	    (begin (display "exception: returning 0")
1054 		   0)))
1055  0)
1056 (test-eval
1057   '(let ((a 4) (b 2))
1058     (unless (= b 0)
1059             (/ a b)
1060 	    (begin (display "exception: returning 0")
1061 		   0)))
1062   2)
1063 
1064 (geval
1065  '(define (factorial n)
1066     (unless (= n 1)
1067             (* n (factorial (- n 1)))
1068 	    1)))
1069 (test-eval
1070  '(factorial 8)
1071  40320)
1072 
1073 (geval '(define count 0))
1074 (geval '(define (id x)
1075 	  (set! count (+ count 1))
1076 	  x))
1077 
1078 (geval '(define w (id (id 10))))
1079 (test-eval 'count 1)
1080 (test-eval 'w 10)
1081 (test-eval 'count 2)
1082 (test-eval
1083  '(let ((f (lambda (x) (+ x 1))))
1084     (f 1))
1085  2)
1086 (geval '(define count 0))
1087 (geval '(define (id x)
1088 	  (set! count (+ count 1))
1089 	  x))
1090 (geval 
1091  '(define (square x)
1092     (* x x)))
1093 (test-eval 
1094  '(square (id 10))
1095  100)
1096 (test-eval 'count 1)
1097 ;; would be 2 without memoization
1098 
1099 
1100 ;; streams
1101 
1102 (geval 
1103  '(define ones (cons 1 ones)))
1104 (geval
1105  '(define integers (cons 1 (add-lists ones integers))))
1106 (test-eval 
1107  '(list-ref integers 17)
1108  18)
1109 
1110 (geval
1111  '(define (integral integrand initial-value dt)
1112     (define int
1113       (cons initial-value
1114 	    (add-lists (scale-list integrand dt)
1115 		       int)))
1116     int))
1117 (geval
1118  '(define (solve f y0 dt)
1119     (define y (integral dy y0 dt))
1120     (define dy (map f y))
1121     y))
1122 (test-eval 
1123  '(list-ref (solve (lambda (x) x) 1 0.001) 1000)
1124  2.716924)