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 
102 ;; assignment/definition
103 (define (assignment? exp)
104   (tagged-list? exp 'set!))
105 (define (assignment-variable exp) (cadr exp))
106 (define (assignment-value exp) (caddr exp))
107 (define (make-assignment var val)
108   (list 'set! var val))
109 (define (definition? exp)
110   (tagged-list? exp 'define))
111 (define (definition-variable exp)
112   (if (symbol? (cadr exp))
113       (cadr exp)
114       (caadr exp)))
115 (define (definition-value exp)
116   (if (symbol? (cadr exp))
117       (caddr exp)
118       (make-lambda (cdadr exp)   ; formal parameters
119                    (cddr exp)))) ; body
120 (define (eval-assignment exp env)
121   (set-variable-value! (assignment-variable exp)
122                        (eval (assignment-value exp) env)
123                        env)
124   'ok)
125 (define (eval-definition exp env)
126   (define-variable! (definition-variable exp)
127                     (eval (definition-value exp) env)
128                     env)
129   'ok)
130 (define (make-definition var val)
131   `(define ,var ,val))
132 
133 ;; make-unbound!
134 
135 ;; (define (unbound? exp)
136 ;;   (tagged-list? exp 'make-unbound!))
137 ;; (define (unbound-var exp)
138 ;;   (cadr exp))
139 ;; (define (eval-unbound exp env)
140 ;;   (remove-binding-from-frame! (unbound-var exp) (first-frame env)))
141 
142 
143 
144 ;; if/and/or
145 (define (if? exp) (tagged-list? exp 'if))
146 (define (if-predicate exp) (cadr exp))
147 (define (if-consequent exp) (caddr exp))
148 (define (if-alternative exp)
149   (if (not (null? (cdddr exp)))
150       (cadddr exp)
151       'false))
152 (define (make-if predicate consequent alternative)
153   (list 'if predicate consequent alternative))
154 (define (eval-if exp env)
155   (if (true? (actual-value (if-predicate exp) env))
156       (eval (if-consequent exp) env)
157       (eval (if-alternative exp) env)))
158 
159 (define (and? exp)
160   (tagged-list? exp 'and))
161 (define (and-clauses exp)
162   (cdr exp))
163 (define (or? exp)
164   (tagged-list? exp 'or))
165 (define (or-clauses exp)
166   (cdr exp))
167 (define (eval-and exp env)
168   (define (eval-clauses clauses)
169     (cond ((null? clauses) true)
170 	  ((null? (cdr clauses)) (eval (car clauses) env))
171 	  (else (and (eval (car clauses) env)
172 		     (eval-clauses (cdr clauses))))))
173   (eval-clauses (and-clauses exp)))
174 (define (eval-or exp env)
175   (define (eval-clauses clauses)
176     (if (null? clauses)
177 	false
178 	(or (eval (car clauses) env)
179 	    (eval-clauses (cdr clauses)))))
180   (eval-clauses (or-clauses exp)))
181 
182 
183 ;; lambda/let/let*/letrec
184 (define (lambda? exp) (tagged-list? exp 'lambda))
185 (define (lambda-parameters exp) (cadr exp))
186 (define (lambda-body exp) (cddr exp))
187 (define (make-lambda parameters body)
188   (cons 'lambda (cons parameters body)))
189 
190 (define (make-let vars vals body)
191   (cons 'let
192 	(cons (map list vars vals)
193 	      body)))
194 (define (let? exp)
195   (and (tagged-list? exp 'let)
196        (not (symbol? (cadr exp)))))
197 (define (let-vars exp)
198   (map car (cadr exp)))
199 (define (let-vals exp)
200   (map cadr (cadr exp)))
201 (define (let-body exp)
202   (cddr exp))
203 (define (let->combination exp)
204   (make-application (make-lambda (let-vars exp) (let-body exp))
205 		    (let-vals exp)))
206 (define (named-let? exp)
207   (and (tagged-list? exp 'let)
208        (symbol? (cadr exp))))
209 (define (named-let-name exp)
210   (cadr exp))
211 (define (named-let-vars exp)
212   (map car (caddr exp)))
213 (define (named-let-vals exp)
214   (map cadr (caddr exp)))
215 (define (named-let-body exp)
216   (cdddr exp))
217 (define (named-let->combination exp)
218   (sequence->exp
219    (list (make-definition (named-let-name exp)
220 			  (make-lambda (named-let-vars exp)
221 				       (named-let-body exp)))
222 	 (make-application (named-let-name exp)
223 			   (named-let-vals exp)))))
224 (define (make-named-let name vars vals body)
225   (cons 'let 
226 	(cons name
227 	      (cons (map list vars vals)
228 		    body))))
229 
230 (define (letrec? exp)
231   (tagged-list? exp 'letrec))
232 
233 (define (letrec-vars exp)
234   (map car (cadr exp)))
235 (define (letrec-vals exp)
236   (map cadr (cadr exp)))
237 (define (letrec-body exp)
238   (cddr exp))
239 (define (letrec->let exp)
240   (let* ((vars (letrec-vars exp))
241 	 (unassigneds (map (lambda (var) ''*unassigned*)
242 			   vars))
243 	 (vals (letrec-vals exp))
244 	 (assignments (map (lambda (var val)
245 			     (make-assignment var val))
246 			   vars
247 			   vals))
248 	 (body (letrec-body exp)))
249   (make-let vars 
250 	    unassigneds
251 	    (append assignments body))))
252 
253 
254 
255 
256 (define (let*? exp)
257   (tagged-list? exp 'let*))
258 (define let*-vars let-vars)
259 (define let*-vals let-vals)
260 (define let*-body let-body)
261 (define (let*->nested-lets exp)
262   (define (expand-lets vars vals)
263     (if (null? (cdr vars))
264 	(make-let (list (car vars)) 
265 		  (list (car vals))
266 		  (let*-body exp))
267 	(make-let (list (car vars))
268 		  (list (car vals))
269 		  (list (expand-lets (cdr vars) (cdr vals))))))
270   (let ((vars (let*-vars exp))
271 	(vals (let*-vals exp)))
272     (if (null? vars)
273 	(sequence->exp (let*-body exp))
274 	(expand-lets vars vals))))
275 
276 ;; do loop
277 (define (do? exp)
278   (tagged-list? exp 'do))
279 (define (do-vars exp)
280   (map car (cadr exp)))
281 (define (do-inits exp)
282   (map cadr (cadr exp)))
283 (define (do-steps exp)
284   (map (lambda (var-init-step)
285 	 (if (null? (cddr var-init-step))
286 	     (car var-init-step)
287 	     (caddr var-init-step)))
288        (cadr exp)))
289 (define (do-test exp)
290   (caaddr exp))
291 (define (do-expressions exp)
292   (if (null? (cdaddr exp))
293       (caddr exp)
294       (cdaddr exp)))
295 (define (do-commands exp)
296   (cdddr exp))
297 (define (do->combination exp)
298   (make-named-let
299    'do-iter
300    (do-vars exp)
301    (do-inits exp)
302    (list
303     (make-if
304      (do-test exp)
305      (sequence->exp (do-expressions exp))
306      (sequence->exp
307       (append (do-commands exp)
308 	      (list (make-application
309 		     'do-iter
310 		     (do-steps exp)))))))))
311 
312 
313 ;; begin/sequence
314 (define (begin? exp) (tagged-list? exp 'begin))
315 (define (begin-actions exp) (cdr exp))
316 (define (last-exp? seq) (null? (cdr seq)))
317 (define (first-exp seq) (car seq))
318 (define (rest-exps seq) (cdr seq))
319 (define (sequence->exp seq)
320   (cond ((null? seq) seq)
321         ((last-exp? seq) (first-exp seq))
322         (else (make-begin seq))))
323 (define (make-begin seq) (cons 'begin seq))
324 (define (eval-sequence exps env)
325   (cond ((last-exp? exps) (eval (first-exp exps) env))
326         (else (eval (first-exp exps) env)
327               (eval-sequence (rest-exps exps) env))))
328 
329 ;; application
330 (define (make-application op args)
331   (cons op args))
332 (define (application? exp) (pair? exp))
333 (define (operator exp) (car exp))
334 (define (operands exp) (cdr exp))
335 (define (no-operands? ops) (null? ops))
336 (define (first-operand ops) (car ops))
337 (define (rest-operands ops) (cdr ops))
338 
339 ;; cond
340 (define (cond? exp) (tagged-list? exp 'cond))
341 (define (cond-clauses exp) (cdr exp))
342 (define (cond-else-clause? clause)
343   (eq? (cond-predicate clause) 'else))
344 (define (cond-predicate clause) (car clause))
345 (define (cond-actions clause) (cdr clause))
346 (define (cond-extended-clause? clause)
347   (and (not (null? (cdr clause))) (eq? (cadr clause) '=>)))
348 (define (cond-extended-proc clause)
349   (caddr clause))
350 (define (cond->if exp)
351   (expand-clauses (cond-clauses exp)))
352 (define (expand-clauses clauses)
353   (if (null? clauses)
354       'false                          ; no else clause
355       (let ((first (car clauses))
356             (rest (cdr clauses)))
357         (if (cond-else-clause? first)
358             (if (null? rest)
359                 (sequence->exp (cond-actions first))
360                 (error "ELSE clause isn't last -- COND->IF"
361                        clauses))
362 	    (if (cond-extended-clause? first)
363 		(make-if (cond-predicate first)
364 			 (make-application
365 			  (cond-extended-proc first)
366 			  (list (cond-predicate first)))
367 			 (expand-clauses rest))
368 		(make-if (cond-predicate first)
369 			 (sequence->exp (cond-actions first))
370 			 (expand-clauses rest)))))))
371 (define (true? x)
372   (not (eq? x false)))
373 (define (false? x)
374   (eq? x false))
375 
376 ;; procedure
377 (define (make-procedure parameters body env)
378   (list 'procedure parameters body env))
379 ;; (define (scan-out-defines body)
380 ;;   (let* ((definitions (filter definition? body))
381 ;; 	 (vars (map definition-variable definitions))
382 ;; 	 (unassigneds (map (lambda (var) ''*unassigned*) 
383 ;; 			   vars))
384 ;; 	 (vals (map definition-value definitions))
385 ;; 	 (assignments 
386 ;; 	  (map (lambda (var val)
387 ;; 		 (make-assignment var val))
388 ;; 	       vars vals))
389 ;; 	 (exps (remove definition? body)))
390 ;;     (if (null? definitions)
391 ;; 	body
392 ;; 	(list
393 ;; 	 (make-let vars
394 ;; 		   unassigneds
395 ;; 		   (append assignments exps))))))
396 (define (compound-procedure? p)
397   (tagged-list? p 'procedure))
398 (define (procedure-parameters p) (cadr p))
399 (define (procedure-body p) (caddr p))
400 (define (procedure-environment p) (cadddr p))
401 
402 ;; environment
403 (define (enclosing-environment env) (cdr env))
404 (define (first-frame env) (car env))
405 (define the-empty-environment '())
406 (define (make-frame variables values)
407   (cons variables values))
408 (define (frame-variables frame) (car frame))
409 (define (frame-values frame) (cdr frame))
410 (define (add-binding-to-frame! var val frame)
411   (set-car! frame (cons var (car frame)))
412   (set-cdr! frame (cons val (cdr frame))))
413 (define (extend-environment vars vals base-env)
414   (if (= (length vars) (length vals))
415       (cons (make-frame vars vals) base-env)
416       (if (< (length vars) (length vals))
417           (error "Too many arguments supplied" vars vals)
418           (error "Too few arguments supplied" vars vals))))
419 (define (lookup-variable-value var env)
420   (define (env-loop env)
421     (define (scan vars vals)
422       (cond ((null? vars)
423              (env-loop (enclosing-environment env)))
424             ((eq? var (car vars))
425 	     (let ((val (car vals)))
426 	       (if (eq? val '*unassigned*)
427 		   (error "Var not yet defined -- LOOKUP-VARIABLE-VALUE" var)
428 		   val)))
429             (else (scan (cdr vars) (cdr vals)))))
430     (if (eq? env the-empty-environment)
431         (error "Unbound variable" var)
432         (let ((frame (first-frame env)))
433           (scan (frame-variables frame)
434                 (frame-values frame)))))
435   (env-loop env))
436 (define (set-variable-value! var val env)
437   (define (env-loop env)
438     (define (scan vars vals)
439       (cond ((null? vars)
440              (env-loop (enclosing-environment env)))
441             ((eq? var (car vars))
442              (set-car! vals val))
443             (else (scan (cdr vars) (cdr vals)))))
444     (if (eq? env the-empty-environment)
445         (error "Unbound variable -- SET!" var)
446         (let ((frame (first-frame env)))
447           (scan (frame-variables frame)
448                 (frame-values frame)))))
449   (env-loop env))
450 (define (define-variable! var val env)
451   (let ((frame (first-frame env)))
452     (define (scan vars vals)
453       (cond ((null? vars)
454              (add-binding-to-frame! var val frame))
455             ((eq? var (car vars))
456              (set-car! vals val))
457             (else (scan (cdr vars) (cdr vals)))))
458     (scan (frame-variables frame)
459           (frame-values frame))))
460 
461 (define (remove-binding-from-frame! var frame)
462   (define (scan vars vals)
463     (cond ((null? (cdr vars))
464 	   (error "Binding not found -- REMOVE-BINDING-FROM-FRAME!" var))
465 	  ((eq? var (cadr vars))
466 	   (set-cdr! vars (cddr vars))
467 	   (set-cdr! vals (cddr vals)))
468 	  (else (scan (cdr vars) (cdr vals)))))
469   (let ((vars (frame-variables frame))
470 	(vals (frame-values frame)))
471     (if (eq? var (car vars))
472 	(begin (set-car! frame (cdr vars))
473 	       (set-cdr! frame (cdr vals)))
474 	(scan vars vals))))
475 
476 ;; primitives
477 (define (primitive-procedure? proc)
478   (tagged-list? proc 'primitive))
479 (define (primitive-implementation proc) (cadr proc))
480 (define primitive-procedures
481   (list (list 'car car)
482         (list 'cdr cdr)
483 	(list 'caar caar)
484 	(list 'cadr cadr)
485 	(list 'cddr cddr)
486         (list 'cons cons)
487         (list 'null? null?)
488 	(list '* *)
489 	(list '/ /)
490 	(list '+ +)
491 	(list '- -)
492 	(list '= =)
493 	(list '< <)
494 	(list '> >)
495 	(list '<= <=)
496 	(list '>= >=)
497 	(list 'remainder remainder)
498 	(list 'eq? eq?)
499 	(list 'equal? equal?)
500 	(list 'display display)))
501 (define (primitive-procedure-names)
502   (map car
503        primitive-procedures))
504 (define (primitive-procedure-objects)
505   (map (lambda (proc) (list 'primitive (cadr proc)))
506        primitive-procedures))
507 (define (apply-primitive-procedure proc args)
508   (apply-in-underlying-scheme
509    (primitive-implementation proc) args))
510 
511 ;; driver-loop
512 (define input-prompt ";;; M-Eval input:")
513 (define output-prompt ";;; M-Eval value:")
514 (define (driver-loop)
515   (prompt-for-input input-prompt)
516   (let ((input (read)))
517     (let ((output (actual-value input the-global-environment)))
518       (announce-output output-prompt)
519       (user-print output)))
520   (driver-loop))
521 (define (prompt-for-input string)
522   (newline) (newline) (display string) (newline))
523 
524 (define (announce-output string)
525   (newline) (display string) (newline))
526 (define (user-print object)
527   (if (compound-procedure? object)
528       (display (list 'compound-procedure
529                      (procedure-parameters object)
530                      (procedure-body object)
531                      '<procedure-env>))
532       (display object)))
533 (define (setup-environment)
534   (let ((initial-env
535          (extend-environment (primitive-procedure-names)
536                              (primitive-procedure-objects)
537                              the-empty-environment)))
538     (define-variable! 'true true initial-env)
539     (define-variable! 'false false initial-env)
540     initial-env))
541 (define the-global-environment (setup-environment))
542 
543 ;; auxiliary
544 (define (test-case actual expected)
545   (newline)
546   (display "Actual:   ")
547   (display actual)
548   (newline)
549   (display "Expected: ")
550   (display expected)
551   (newline))
552 (define (geval exp) ;; eval globally
553   (eval exp the-global-environment))
554 (define (test-eval exp expected)
555   (test-case (force-it (geval exp)) expected))
556 
557 ;; Exercise 4.33.  Ben Bitdiddle tests the lazy list implementation given above by evaluating the expression
558 
559 (define (quoted-list? exp)
560   (and (tagged-list? exp 'quote)
561        (pair? (cadr exp))))
562 
563 (define (list->cons exp)
564   (if (pair? exp)
565       (make-cons (list->cons (car exp))
566 		 (list->cons (cdr exp)))
567       (make-quote exp)))
568 (define (make-quote exp)
569   `(quote ,exp))
570 (define (make-cons x y)
571   `(cons ,x ,y))
572 
573 ;; (car '(a b c))
574 
575 ;; if we have a quoted list, we need to transform it into the proper cons
576 
577 ;; To his surprise, this produces an error. After some thought, he realizes that the ``lists'' obtained by reading in quoted expressions are different from the lists manipulated by the new definitions of cons, car, and cdr. Modify the evaluator's treatment of quoted expressions so that quoted lists typed at the driver loop will produce true lazy lists. 
578 
579 ;; (quote (a))
580 (test-eval
581  '(car (cons (quote a) (quote ())))
582  'a)
583 (test-eval
584  '(cdr (cons (quote a) (quote ())))
585  '())
586 (test-eval
587  '(car '(a))
588  'a)
589 (test-eval
590  '(cdr '(a))
591  '())
592 (test-eval
593  '(car (cdr '(a b)))
594  'b)
595 (test-eval
596  '(car (car '((a b) c)))
597  'a)
598 (test-eval
599  '(car (cdr (car (cdr '((a c) (b d))))))
600  'd)
601 
602 
603 
604 ;; cons/car/cdr
605 
606 (geval 
607  '(define (cons x y)
608     (lambda (m) (m x y))))
609 (geval
610  '(define (car z)
611     (z (lambda (p q) p))))
612 (geval
613  '(define (cdr z)
614     (z (lambda (p q) q))))
615 (geval
616  '(define (list-ref items n)
617     (if (= n 0)
618 	(car items)
619 	(list-ref (cdr items) (- n 1)))))
620 (geval
621  '(define (map proc items)
622     (if (null? items)
623 	'()
624 	(cons (proc (car items))
625 	      (map proc (cdr items))))))
626 (geval
627  '(define (scale-list items factor)
628     (map (lambda (x) (* x factor))
629 	 items)))
630 (geval
631  '(define (add-lists list1 list2)
632     (cond ((null? list1) list2)
633 	  ((null? list2) list1)
634 	  (else (cons (+ (car list1) (car list2))
635 		      (add-lists (cdr list1) (cdr list2)))))))
636 
637 
638 
639 (geval 
640  '(define ones (cons 1 ones)))
641 (geval
642  '(define integers (cons 1 (add-lists ones integers))))
643 (test-eval 
644  '(list-ref integers 17)
645  18)
646 
647 (test-eval
648  '(car (cdr (add-lists '(1 2 3 4 5) '(2 3 4 5 6))))
649  5)
650 
651 (geval
652  '(define (integral integrand initial-value dt)
653     (define int
654       (cons initial-value
655 	    (add-lists (scale-list integrand dt)
656 		       int)))
657     int))
658 (geval
659  '(define (solve f y0 dt)
660     (define y (integral dy y0 dt))
661     (define dy (map f y))
662     y))
663 (test-eval 
664  '(list-ref (solve (lambda (x) x) 1 0.001) 1000)
665  2.716924)
666 
667 
668 ;; test-suite
669 
670 ;; procedure definitions
671 
672 (geval 
673  '(define (assoc key records)
674     (cond ((null? records) false)
675 	  ((equal? key (caar records)) (car records))
676 	  (else (assoc key (cdr records))))))
677 
678 (geval
679  '(define (map proc list)
680     (if (null? list)
681 	'()
682 	(cons (proc (car list))
683 	      (map proc (cdr list))))))
684 
685 (geval 
686  '(define (accumulate op initial sequence)
687     (if (null? sequence)
688 	initial
689 	(op (car sequence)
690 	    (accumulate op initial (cdr sequence))))))
691 
692 ;; all special forms
693 (test-eval '(begin 5 6) 6)
694 (test-eval '10 10)
695 (geval '(define x 3))
696 (test-eval 'x 3)
697 (test-eval '(set! x -25) 'ok)
698 (test-eval 'x -25)
699 (geval '(define z (lambda (x y) (+ x (* x y)))))
700 (test-eval '(z 3 4) 15)
701 (test-eval '(cond ((= x -2) 'x=-2)
702 		  ((= x -25) 'x=-25)
703 		  (else 'failed))
704 	   'x=-25)
705 (test-eval '(if true false true) false)
706 
707 (test-eval 
708  '(let ((x 4) (y 7))
709     (+ x y (* x y)))
710  (+ 4 7 (* 4 7)))
711 
712 
713 ;; and/or
714 (geval '(define x (+ 3 8)))
715 (test-eval '(and 0 true x) 11)
716 (test-eval '(and 0 true x false) false)
717 (test-eval '(and 0 true x (set! x -2) false) false)
718 (test-eval 'x -2)
719 (test-eval '(and 0 true x false (set! x -5)) false)
720 (test-eval 'x -2)
721 (test-eval '(or false (set! x 25)) 'ok)
722 (test-eval 'x 25)
723 (test-eval '(or (set! x 2) (set! x 4)) 'ok)
724 (test-eval 'x 2)
725 (test-eval '(or false (set! x 25) true false) 'ok)
726 (test-eval 'x 25)
727 (test-eval '(or ((lambda (x) x) 5)) 5)
728 (test-eval '(or (begin (set! x (+ x 1)) x)) 26)
729 
730 
731 ;; cond
732 
733 ;; (test-eval 
734 ;;  '(cond ((assoc 'b '((a 1) (b 2))) => cadr)
735 ;; 	(else false))
736 ;;  2)
737 
738 ;; (test-eval
739 ;;  '(cond ((= 3 4) 'not-true)
740 ;; 	((= (* 2 4) 3) 'also-false)
741 ;; 	((map (lambda (x)
742 ;; 		(* x (+ x 1)))
743 ;; 	      '(2 4 1 9))
744 ;; 	 =>
745 ;; 	 (lambda (x)
746 ;; 	   (accumulate + 0 x)))
747 ;; 	(else 'never-reach))
748 ;;  118)
749 ;; '(6 20 2 90)
750 
751 
752 ;; procedure definition and application
753 (geval
754  '(define (factorial n)
755     (if (= n 0)
756 	1
757 	(* n (factorial (- n 1))))))
758 (test-eval '(factorial 5) 120)
759 
760 ;; map
761 
762 ;; (test-eval
763 ;;  '(map (lambda (x)
764 ;; 	 (* x (+ x 1)))
765 ;;        '(2 1 4 2 8 3))
766 ;;  '(6 2 20 6 72 12))
767 ;; accumulate
768 
769 (test-eval
770  '(accumulate + 0 '(1 2 3 4 5))
771  15)
772 
773 ;; make-let
774 (test-eval 
775  (make-let '(x y) '(3 5) '((+ x y)))
776  8)
777 (test-eval 
778  '(let ()
779     5)
780  5)
781 (test-eval
782  '(let ((x 3))
783     x)
784  3)
785 (test-eval
786  '(let ((x 3)
787 	(y 5))
788     (+ x y))
789  8)
790 (test-eval 
791  '(let ((x 3)
792 	(y 2))
793     (+ (let ((x (+ y 2))
794 	     (y x))
795 	 (* x y))
796        x y))
797  (+ (* 4 3) 3 2))
798 (test-eval
799  '(let ((x 6)
800 	(y (let ((x 2))
801 	     (+ x 3)))
802 	(z (let ((a (* 3 2)))
803 	     (+ a 3))))
804     (+ x y z))
805  (+ 6 5 9))
806     
807 
808 ;; let*
809 
810 (test-eval
811  '(let* ((x 3)
812 	 (y (+ x 2))
813 	 (z (+ x y 5)))
814     (* x z))
815  39)
816 
817 (test-eval
818  '(let* ()
819     5)
820  5)
821 (test-eval
822  '(let* ((x 3))
823     (let* ((y 5))
824       (+ x y)))
825  8)
826 
827 (test-eval 
828  '(let* ((x 3)
829 	 (y (+ x 1)))
830     (+ (let* ((x (+ y 2))
831 	      (y x))
832 	 (* x y))
833        x y))
834  (+ (* 6 6) 3 4))
835 (test-eval
836  '(let* ((x 6)
837 	 (y (let* ((x 2)
838 		   (a (let* ((x (* 3 x)))
839 			(+ x 2))))       
840 	      (+ x a)))                  
841 	 (z (+ x y)))                    
842     (+ x y z))
843  32)
844 
845 ;; named-let
846 
847 (test-eval
848  '(let eight ()
849     5
850     7
851     8)
852  8)
853 (test-eval
854  '(let loop ((count 0))
855     (if (= 100 count)
856 	count
857 	(loop (+ count 1))))
858  100)
859 (geval
860  '(define (prime? x)
861     (let prime-iter ((i 2))
862       (cond ((> (* i i) x) true)
863 	    ((= (remainder x i) 0) false)
864 	    (else (prime-iter (+ i 1)))))))
865 ;; (test-eval
866 ;;  '(let primes ((x 2)
867 ;; 	       (n 20))
868 ;;     (cond ((= n 0) '())
869 ;; 	  ((prime? x) 
870 ;; 	   (cons x
871 ;; 		 (primes (+ x 1) (- n 1))))
872 ;; 	  (else (primes (+ x 1) n))))
873 ;;  '(2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71))
874 
875 (geval
876  '(define (fib n)
877     (let fib-iter ((a 1)
878 		   (b 0)
879 		   (count n))
880       (if (= count 0)
881 	  b
882 	  (fib-iter (+ a b) a (- count 1))))))
883 (test-eval '(fib 19) 4181)
884 
885 ;; do-loop	  
886 (test-eval
887  '(let ((y 0))
888     (do ((x 0 (+ x 1)))
889 	((= x 5) y)
890       (set! y (+ y 1))))
891  5)
892 (test-eval
893  '(do ()
894       (true))
895  true)
896 (test-eval
897  '(do ()
898       (true 5))
899  5)
900 (test-eval
901  '(let ((y 0))
902     (do ()
903 	((= y 5) y)
904       (set! y (+ y 1))))
905  5)
906 
907 (test-eval
908  '(do ((y '(1 2 3 4)))
909       ((null? y))
910     (set! y (cdr y)))
911  true)
912 (test-eval
913  '(let ((y 0))
914     (do ((x 0 (+ x 1)))
915 	((= x 5) y)
916       (set! y (+ y 1))))
917  5)
918 (test-eval
919  '(let ((x '(1 3 5 7 9)))
920     (do ((x x (cdr x))
921 	 (sum 0 (+ sum (car x))))
922 	((null? x) sum)))
923  25)
924 ;; (test-eval 
925 ;;  '(let ((z '()))
926 ;;     (do ((x '(1 2 3 4) (cdr x))
927 ;; 	 (y '(1 2 3 4 5 6 7 8) (cddr y)))
928 ;; 	((null? x) y x z)
929 ;;       (set! z (cons (car x) z))))
930 ;;  '(4 3 2 1))
931 
932 
933 
934 ;; make-unbound!
935 ;; broken now due to scan-out-defines
936 
937 ;; (test-eval
938 ;;  '(let ((x 3))
939 ;;     (let ((x 5))
940 ;;       (make-unbound! x)
941 ;;       (* x x)))
942 ;;  9)
943 
944 ;; (test-eval
945 ;;  '(let ((x 3))
946 ;;     (let ((x 5))
947 ;;       (define y x)
948 ;;       (make-unbound! x)
949 ;;       (* y x)))
950 ;;  15)
951 
952 ;; (test-eval
953 ;;  '(let ((y -1) (x 3))
954 ;;     (let ((y 0.5) (x 5))
955 ;;       (define a x)
956 ;;       (define b y)
957 ;;       (make-unbound! x)
958 ;;       (make-unbound! y)
959 ;;       (* a b x y)))
960 ;;  (* 5 3 -1 0.5))
961 
962 ;; (test-eval
963 ;;  '(let ((x 3) (y 4))
964 ;;     (let ((x 5))
965 ;;       (make-unbound! x)
966 ;;       (+ x 4)))
967 ;;  7)
968 
969 ;; (test-eval 
970 ;;  '(let ((a 1) (b 2) (c 3) (d 4))
971 ;;     (make-unbound! b)
972 ;;     (+ a c d))
973 ;;  (+ 1 3 4))
974 
975 ;; (test-eval
976 ;;  '(let ((x 4) (y 5))
977 ;;     (let ((a 1) (b 2) (c 3))
978 ;;       (let ((x (+ a b)) (y (+ c a)))
979 ;; 	(make-unbound! x)
980 ;; 	(let ((a x) (b (+ x y)))
981 ;; 	  (define z b)
982 ;; 	  (make-unbound! b)
983 ;; 	  (* (+ a z)
984 ;; 	     (+ a b y))))))
985 ;;  (* (+ 4 8)
986 ;;     (+ 4 2 4)))
987  
988 ;; x 3 -- y 4
989 ;; x 4 -- y 4
990 ;; a 4 -- b 4
991 ;; a 4 -- b 2
992 
993 ;; scan-out-defines
994 
995 (geval
996  '(define (f x)
997     (define (even? n)
998       (if (= n 0)
999 	  true
1000 	  (odd? (- n 1))))
1001     (define (odd? n)
1002       (if (= n 0)
1003 	  false
1004 	  (even? (- n 1))))
1005     (even? x)))
1006 (test-eval '(f 5) false)
1007 (test-eval '(f 10) true)
1008 
1009 ;; (geval
1010 ;;  '(let ((x 5))
1011 ;;     (define y x)
1012 ;;     (define x 3)
1013 ;;     (+ x y)))
1014 ;; signal an error because x is undefined if variables are scanned out
1015 
1016 ;; letrec
1017 
1018 (geval
1019  '(define (f x)
1020     (letrec ((even?
1021 	      (lambda (n)
1022 		(if (= n 0)
1023 		    true
1024 		    (odd? (- n 1)))))
1025 	     (odd?
1026 	      (lambda (n)
1027 		(if (= n 0)
1028 		    false
1029 		    (even? (- n 1))))))
1030       (even? x))))
1031 (test-eval '(f 11) false)
1032 (test-eval '(f 16) true)
1033 
1034 (test-eval 
1035  '(letrec ((fact
1036 	    (lambda (n)
1037 	      (if (= n 1)
1038 		  1
1039 		  (* n (fact (- n 1)))))))
1040     (fact 10))
1041  3628800)
1042 
1043 
1044 ;; delayed-evaluation
1045 
1046 (geval
1047  '(define (try a b)
1048     (if (= a 0) 1 b)))
1049 (test-eval '(try 0 (/ 1 0)) 1)
1050 
1051 (geval 
1052  '(define (unless condition usual-value exceptional-value)
1053     (if condition exceptional-value usual-value)))
1054 (test-eval
1055  '(let ((a 4) (b 0))
1056     (unless (= b 0)
1057             (/ a b)
1058 	    (begin (display "exception: returning 0")
1059 		   0)))
1060  0)
1061 (test-eval
1062   '(let ((a 4) (b 2))
1063     (unless (= b 0)
1064             (/ a b)
1065 	    (begin (display "exception: returning 0")
1066 		   0)))
1067   2)
1068 
1069 (geval
1070  '(define (factorial n)
1071     (unless (= n 1)
1072             (* n (factorial (- n 1)))
1073 	    1)))
1074 (test-eval
1075  '(factorial 8)
1076  40320)
1077 
1078 (geval '(define count 0))
1079 (geval '(define (id x)
1080 	  (set! count (+ count 1))
1081 	  x))
1082 
1083 (geval '(define w (id (id 10))))
1084 (test-eval 'count 1)
1085 (test-eval 'w 10)
1086 (test-eval 'count 2)
1087 (test-eval
1088  '(let ((f (lambda (x) (+ x 1))))
1089     (f 1))
1090  2)
1091 (geval '(define count 0))
1092 (geval '(define (id x)
1093 	  (set! count (+ count 1))
1094 	  x))
1095 (geval 
1096  '(define (square x)
1097     (* x x)))
1098 (test-eval 
1099  '(square (id 10))
1100  100)
1101 (test-eval 'count 1)
1102 ;; would be 2 without memoization
1103 
1104 
1105 ;; streams
1106 
1107 (geval 
1108  '(define ones (cons 1 ones)))
1109 (geval
1110  '(define integers (cons 1 (add-lists ones integers))))
1111 (test-eval 
1112  '(list-ref integers 17)
1113  18)
1114 
1115 (geval
1116  '(define (integral integrand initial-value dt)
1117     (define int
1118       (cons initial-value
1119 	    (add-lists (scale-list integrand dt)
1120 		       int)))
1121     int))
1122 (geval
1123  '(define (solve f y0 dt)
1124     (define y (integral dy y0 dt))
1125     (define dy (map f y))
1126     y))
1127 (test-eval 
1128  '(list-ref (solve (lambda (x) x) 1 0.001) 1000)
1129  2.716924)