1 665c255d 2023-08-04 jrmu (define (eval exp env)
2 665c255d 2023-08-04 jrmu (cond ((self-evaluating? exp) exp)
3 665c255d 2023-08-04 jrmu ((variable? exp) (lookup-variable-value exp env))
4 665c255d 2023-08-04 jrmu ((quoted? exp) (text-of-quotation exp))
5 665c255d 2023-08-04 jrmu ((assignment? exp) (eval-assignment exp env))
6 665c255d 2023-08-04 jrmu ((definition? exp) (eval-definition exp env))
7 665c255d 2023-08-04 jrmu ((if? exp) (eval-if exp env))
8 665c255d 2023-08-04 jrmu ((and? exp) (eval-and exp env))
9 665c255d 2023-08-04 jrmu ((or? exp) (eval-or exp env))
10 665c255d 2023-08-04 jrmu ((lambda? exp)
11 665c255d 2023-08-04 jrmu (make-procedure (lambda-parameters exp)
12 665c255d 2023-08-04 jrmu (lambda-body exp)
14 665c255d 2023-08-04 jrmu ((begin? exp)
15 665c255d 2023-08-04 jrmu (eval-sequence (begin-actions exp) env))
16 665c255d 2023-08-04 jrmu ((cond? exp) (eval (cond->if exp) env))
17 665c255d 2023-08-04 jrmu ((let? exp) (eval (let->combination exp) env))
18 665c255d 2023-08-04 jrmu ((let*? exp) (eval (let*->nested-lets exp) env))
19 665c255d 2023-08-04 jrmu ((named-let? exp) (eval (named-let->combination exp) env))
20 665c255d 2023-08-04 jrmu ((application? exp)
21 665c255d 2023-08-04 jrmu (apply (eval (operator exp) env)
22 665c255d 2023-08-04 jrmu (list-of-values (operands exp) env)))
24 665c255d 2023-08-04 jrmu (error "Unknown expression type -- EVAL" exp))))
25 665c255d 2023-08-04 jrmu (define (apply procedure arguments)
26 665c255d 2023-08-04 jrmu (cond ((primitive-procedure? procedure)
27 665c255d 2023-08-04 jrmu (apply-primitive-procedure procedure arguments))
28 665c255d 2023-08-04 jrmu ((compound-procedure? procedure)
29 665c255d 2023-08-04 jrmu (eval-sequence
30 665c255d 2023-08-04 jrmu (procedure-body procedure)
31 665c255d 2023-08-04 jrmu (extend-environment
32 665c255d 2023-08-04 jrmu (procedure-parameters procedure)
34 665c255d 2023-08-04 jrmu (procedure-environment procedure))))
37 665c255d 2023-08-04 jrmu "Unknown procedure type -- APPLY" procedure))))
39 665c255d 2023-08-04 jrmu (define (list-of-values exps env)
40 665c255d 2023-08-04 jrmu (if (no-operands? exps)
42 665c255d 2023-08-04 jrmu (cons (eval (first-operand exps) env)
43 665c255d 2023-08-04 jrmu (list-of-values (rest-operands exps) env))))
45 665c255d 2023-08-04 jrmu (define (tagged-list? exp tag)
46 665c255d 2023-08-04 jrmu (if (pair? exp)
47 665c255d 2023-08-04 jrmu (eq? (car exp) tag)
50 665c255d 2023-08-04 jrmu ;; self-evaluating/variable/quoted
51 665c255d 2023-08-04 jrmu (define (self-evaluating? exp)
52 665c255d 2023-08-04 jrmu (cond ((number? exp) true)
53 665c255d 2023-08-04 jrmu ((string? exp) true)
54 665c255d 2023-08-04 jrmu (else false)))
55 665c255d 2023-08-04 jrmu (define (variable? exp) (symbol? exp))
56 665c255d 2023-08-04 jrmu (define (quoted? exp)
57 665c255d 2023-08-04 jrmu (tagged-list? exp 'quote))
58 665c255d 2023-08-04 jrmu (define (text-of-quotation exp) (cadr exp))
60 665c255d 2023-08-04 jrmu ;; assignment/definition
61 665c255d 2023-08-04 jrmu (define (assignment? exp)
62 665c255d 2023-08-04 jrmu (tagged-list? exp 'set!))
63 665c255d 2023-08-04 jrmu (define (assignment-variable exp) (cadr exp))
64 665c255d 2023-08-04 jrmu (define (assignment-value exp) (caddr exp))
65 665c255d 2023-08-04 jrmu (define (definition? exp)
66 665c255d 2023-08-04 jrmu (tagged-list? exp 'define))
67 665c255d 2023-08-04 jrmu (define (definition-variable exp)
68 665c255d 2023-08-04 jrmu (if (symbol? (cadr exp))
70 665c255d 2023-08-04 jrmu (caadr exp)))
71 665c255d 2023-08-04 jrmu (define (definition-value exp)
72 665c255d 2023-08-04 jrmu (if (symbol? (cadr exp))
74 665c255d 2023-08-04 jrmu (make-lambda (cdadr exp) ; formal parameters
75 665c255d 2023-08-04 jrmu (cddr exp)))) ; body
76 665c255d 2023-08-04 jrmu (define (eval-assignment exp env)
77 665c255d 2023-08-04 jrmu (set-variable-value! (assignment-variable exp)
78 665c255d 2023-08-04 jrmu (eval (assignment-value exp) env)
81 665c255d 2023-08-04 jrmu (define (eval-definition exp env)
82 665c255d 2023-08-04 jrmu (define-variable! (definition-variable exp)
83 665c255d 2023-08-04 jrmu (eval (definition-value exp) env)
88 665c255d 2023-08-04 jrmu ;; if/and/or
89 665c255d 2023-08-04 jrmu (define (if? exp) (tagged-list? exp 'if))
90 665c255d 2023-08-04 jrmu (define (if-predicate exp) (cadr exp))
91 665c255d 2023-08-04 jrmu (define (if-consequent exp) (caddr exp))
92 665c255d 2023-08-04 jrmu (define (if-alternative exp)
93 665c255d 2023-08-04 jrmu (if (not (null? (cdddr exp)))
94 665c255d 2023-08-04 jrmu (cadddr exp)
96 665c255d 2023-08-04 jrmu (define (make-if predicate consequent alternative)
97 665c255d 2023-08-04 jrmu (list 'if predicate consequent alternative))
98 665c255d 2023-08-04 jrmu (define (eval-if exp env)
99 665c255d 2023-08-04 jrmu (if (true? (eval (if-predicate exp) env))
100 665c255d 2023-08-04 jrmu (eval (if-consequent exp) env)
101 665c255d 2023-08-04 jrmu (eval (if-alternative exp) env)))
103 665c255d 2023-08-04 jrmu (define (and? exp)
104 665c255d 2023-08-04 jrmu (tagged-list? exp 'and))
105 665c255d 2023-08-04 jrmu (define (and-clauses exp)
107 665c255d 2023-08-04 jrmu (define (or? exp)
108 665c255d 2023-08-04 jrmu (tagged-list? exp 'or))
109 665c255d 2023-08-04 jrmu (define (or-clauses exp)
111 665c255d 2023-08-04 jrmu (define (eval-and exp env)
112 665c255d 2023-08-04 jrmu (define (eval-clauses clauses)
113 665c255d 2023-08-04 jrmu (cond ((null? clauses) true)
114 665c255d 2023-08-04 jrmu ((null? (cdr clauses)) (eval (car clauses) env))
115 665c255d 2023-08-04 jrmu (else (and (eval (car clauses) env)
116 665c255d 2023-08-04 jrmu (eval-clauses (cdr clauses))))))
117 665c255d 2023-08-04 jrmu (eval-clauses (and-clauses exp)))
118 665c255d 2023-08-04 jrmu (define (eval-or exp env)
119 665c255d 2023-08-04 jrmu (define (eval-clauses clauses)
120 665c255d 2023-08-04 jrmu (if (null? clauses)
122 665c255d 2023-08-04 jrmu (or (eval (car clauses) env)
123 665c255d 2023-08-04 jrmu (eval-clauses (cdr clauses)))))
124 665c255d 2023-08-04 jrmu (eval-clauses (or-clauses exp)))
127 665c255d 2023-08-04 jrmu ;; lambda/let/let*
128 665c255d 2023-08-04 jrmu (define (lambda? exp) (tagged-list? exp 'lambda))
129 665c255d 2023-08-04 jrmu (define (lambda-parameters exp) (cadr exp))
130 665c255d 2023-08-04 jrmu (define (lambda-body exp) (cddr exp))
131 665c255d 2023-08-04 jrmu (define (make-lambda parameters body)
132 665c255d 2023-08-04 jrmu (cons 'lambda (cons parameters body)))
134 665c255d 2023-08-04 jrmu (define (make-let vars vals body)
136 665c255d 2023-08-04 jrmu (cons (map (lambda (var val)
137 665c255d 2023-08-04 jrmu (list var val))
140 665c255d 2023-08-04 jrmu (define (let? exp)
141 665c255d 2023-08-04 jrmu (and (tagged-list? exp 'let)
142 665c255d 2023-08-04 jrmu (not (symbol? (cadr exp)))))
143 665c255d 2023-08-04 jrmu (define (let-vars exp)
144 665c255d 2023-08-04 jrmu (map car (cadr exp)))
145 665c255d 2023-08-04 jrmu (define (let-vals exp)
146 665c255d 2023-08-04 jrmu (map cadr (cadr exp)))
147 665c255d 2023-08-04 jrmu (define (let-body exp)
148 665c255d 2023-08-04 jrmu (cddr exp))
149 665c255d 2023-08-04 jrmu (define (let->combination exp)
150 665c255d 2023-08-04 jrmu (make-application (make-lambda (let-vars exp) (let-body exp))
151 665c255d 2023-08-04 jrmu (let-vals exp)))
152 665c255d 2023-08-04 jrmu (define (named-let? exp)
153 665c255d 2023-08-04 jrmu (and (tagged-list? exp 'let)
154 665c255d 2023-08-04 jrmu (symbol? (cadr exp))))
155 665c255d 2023-08-04 jrmu (define (named-let-name exp)
156 665c255d 2023-08-04 jrmu (cadr exp))
157 665c255d 2023-08-04 jrmu (define (named-let-vars exp)
158 665c255d 2023-08-04 jrmu (map car (caddr exp)))
159 665c255d 2023-08-04 jrmu (define (named-let-vals exp)
160 665c255d 2023-08-04 jrmu (map cadr (caddr exp)))
161 665c255d 2023-08-04 jrmu (define (named-let-body exp)
162 665c255d 2023-08-04 jrmu (cdddr exp))
163 665c255d 2023-08-04 jrmu (define (named-let->combination exp)
164 665c255d 2023-08-04 jrmu (sequence->exp
165 665c255d 2023-08-04 jrmu (list (make-definition (named-let-name exp)
166 665c255d 2023-08-04 jrmu (make-lambda (named-let-vars exp)
167 665c255d 2023-08-04 jrmu (named-let-body exp)))
168 665c255d 2023-08-04 jrmu (make-application (named-let-name exp)
169 665c255d 2023-08-04 jrmu (named-let-vals exp)))))
170 665c255d 2023-08-04 jrmu (define (make-definition var val)
171 665c255d 2023-08-04 jrmu `(define ,var ,val))
174 665c255d 2023-08-04 jrmu (define (make-application op args)
175 665c255d 2023-08-04 jrmu (cons op args))
177 665c255d 2023-08-04 jrmu (define (let*? exp)
178 665c255d 2023-08-04 jrmu (tagged-list? exp 'let*))
179 665c255d 2023-08-04 jrmu (define let*-vars let-vars)
180 665c255d 2023-08-04 jrmu (define let*-vals let-vals)
181 665c255d 2023-08-04 jrmu (define let*-body let-body)
182 665c255d 2023-08-04 jrmu (define (let*->nested-lets exp)
183 665c255d 2023-08-04 jrmu (define (expand-lets vars vals)
184 665c255d 2023-08-04 jrmu (if (null? (cdr vars))
185 665c255d 2023-08-04 jrmu (make-let (list (car vars))
186 665c255d 2023-08-04 jrmu (list (car vals))
187 665c255d 2023-08-04 jrmu (let*-body exp))
188 665c255d 2023-08-04 jrmu (make-let (list (car vars))
189 665c255d 2023-08-04 jrmu (list (car vals))
190 665c255d 2023-08-04 jrmu (list (expand-lets (cdr vars) (cdr vals))))))
191 665c255d 2023-08-04 jrmu (let ((vars (let*-vars exp))
192 665c255d 2023-08-04 jrmu (vals (let*-vals exp)))
193 665c255d 2023-08-04 jrmu (if (null? vars)
194 665c255d 2023-08-04 jrmu (sequence->exp (let*-body exp))
195 665c255d 2023-08-04 jrmu (expand-lets vars vals))))
198 665c255d 2023-08-04 jrmu ;; begin/sequence
199 665c255d 2023-08-04 jrmu (define (begin? exp) (tagged-list? exp 'begin))
200 665c255d 2023-08-04 jrmu (define (begin-actions exp) (cdr exp))
201 665c255d 2023-08-04 jrmu (define (last-exp? seq) (null? (cdr seq)))
202 665c255d 2023-08-04 jrmu (define (first-exp seq) (car seq))
203 665c255d 2023-08-04 jrmu (define (rest-exps seq) (cdr seq))
204 665c255d 2023-08-04 jrmu (define (sequence->exp seq)
205 665c255d 2023-08-04 jrmu (cond ((null? seq) seq)
206 665c255d 2023-08-04 jrmu ((last-exp? seq) (first-exp seq))
207 665c255d 2023-08-04 jrmu (else (make-begin seq))))
208 665c255d 2023-08-04 jrmu (define (make-begin seq) (cons 'begin seq))
209 665c255d 2023-08-04 jrmu (define (eval-sequence exps env)
210 665c255d 2023-08-04 jrmu (cond ((last-exp? exps) (eval (first-exp exps) env))
211 665c255d 2023-08-04 jrmu (else (eval (first-exp exps) env)
212 665c255d 2023-08-04 jrmu (eval-sequence (rest-exps exps) env))))
214 665c255d 2023-08-04 jrmu ;; application
215 665c255d 2023-08-04 jrmu (define (application? exp) (pair? exp))
216 665c255d 2023-08-04 jrmu (define (operator exp) (car exp))
217 665c255d 2023-08-04 jrmu (define (operands exp) (cdr exp))
218 665c255d 2023-08-04 jrmu (define (no-operands? ops) (null? ops))
219 665c255d 2023-08-04 jrmu (define (first-operand ops) (car ops))
220 665c255d 2023-08-04 jrmu (define (rest-operands ops) (cdr ops))
223 665c255d 2023-08-04 jrmu (define (cond? exp) (tagged-list? exp 'cond))
224 665c255d 2023-08-04 jrmu (define (cond-clauses exp) (cdr exp))
225 665c255d 2023-08-04 jrmu (define (cond-else-clause? clause)
226 665c255d 2023-08-04 jrmu (eq? (cond-predicate clause) 'else))
227 665c255d 2023-08-04 jrmu (define (cond-predicate clause) (car clause))
228 665c255d 2023-08-04 jrmu (define (cond-actions clause) (cdr clause))
229 665c255d 2023-08-04 jrmu (define (cond-extended-clause? clause)
230 665c255d 2023-08-04 jrmu (and (not (null? (cdr clause))) (eq? (cadr clause) '=>)))
231 665c255d 2023-08-04 jrmu (define (cond-extended-proc clause)
232 665c255d 2023-08-04 jrmu (caddr clause))
233 665c255d 2023-08-04 jrmu (define (cond->if exp)
234 665c255d 2023-08-04 jrmu (expand-clauses (cond-clauses exp)))
235 665c255d 2023-08-04 jrmu (define (expand-clauses clauses)
236 665c255d 2023-08-04 jrmu (if (null? clauses)
237 665c255d 2023-08-04 jrmu 'false ; no else clause
238 665c255d 2023-08-04 jrmu (let ((first (car clauses))
239 665c255d 2023-08-04 jrmu (rest (cdr clauses)))
240 665c255d 2023-08-04 jrmu (if (cond-else-clause? first)
241 665c255d 2023-08-04 jrmu (if (null? rest)
242 665c255d 2023-08-04 jrmu (sequence->exp (cond-actions first))
243 665c255d 2023-08-04 jrmu (error "ELSE clause isn't last -- COND->IF"
245 665c255d 2023-08-04 jrmu (if (cond-extended-clause? first)
246 665c255d 2023-08-04 jrmu (make-if (cond-predicate first)
247 665c255d 2023-08-04 jrmu (make-application
248 665c255d 2023-08-04 jrmu (cond-extended-proc first)
249 665c255d 2023-08-04 jrmu (list (cond-predicate first)))
250 665c255d 2023-08-04 jrmu (expand-clauses rest))
251 665c255d 2023-08-04 jrmu (make-if (cond-predicate first)
252 665c255d 2023-08-04 jrmu (sequence->exp (cond-actions first))
253 665c255d 2023-08-04 jrmu (expand-clauses rest)))))))
254 665c255d 2023-08-04 jrmu (define (true? x)
255 665c255d 2023-08-04 jrmu (not (eq? x false)))
256 665c255d 2023-08-04 jrmu (define (false? x)
257 665c255d 2023-08-04 jrmu (eq? x false))
259 665c255d 2023-08-04 jrmu ;; procedure
260 665c255d 2023-08-04 jrmu (define (make-procedure parameters body env)
261 665c255d 2023-08-04 jrmu (list 'procedure parameters body env))
262 665c255d 2023-08-04 jrmu (define (compound-procedure? p)
263 665c255d 2023-08-04 jrmu (tagged-list? p 'procedure))
264 665c255d 2023-08-04 jrmu (define (procedure-parameters p) (cadr p))
265 665c255d 2023-08-04 jrmu (define (procedure-body p) (caddr p))
266 665c255d 2023-08-04 jrmu (define (procedure-environment p) (cadddr p))
268 665c255d 2023-08-04 jrmu ;; environment
269 665c255d 2023-08-04 jrmu (define (enclosing-environment env) (cdr env))
270 665c255d 2023-08-04 jrmu (define (first-frame env) (car env))
271 665c255d 2023-08-04 jrmu (define the-empty-environment '())
272 665c255d 2023-08-04 jrmu (define (make-frame variables values)
273 665c255d 2023-08-04 jrmu (cons variables values))
274 665c255d 2023-08-04 jrmu (define (frame-variables frame) (car frame))
275 665c255d 2023-08-04 jrmu (define (frame-values frame) (cdr frame))
276 665c255d 2023-08-04 jrmu (define (add-binding-to-frame! var val frame)
277 665c255d 2023-08-04 jrmu (set-car! frame (cons var (car frame)))
278 665c255d 2023-08-04 jrmu (set-cdr! frame (cons val (cdr frame))))
279 665c255d 2023-08-04 jrmu (define (extend-environment vars vals base-env)
280 665c255d 2023-08-04 jrmu (if (= (length vars) (length vals))
281 665c255d 2023-08-04 jrmu (cons (make-frame vars vals) base-env)
282 665c255d 2023-08-04 jrmu (if (< (length vars) (length vals))
283 665c255d 2023-08-04 jrmu (error "Too many arguments supplied" vars vals)
284 665c255d 2023-08-04 jrmu (error "Too few arguments supplied" vars vals))))
285 665c255d 2023-08-04 jrmu (define (lookup-variable-value var env)
286 665c255d 2023-08-04 jrmu (define (env-loop env)
287 665c255d 2023-08-04 jrmu (define (scan vars vals)
288 665c255d 2023-08-04 jrmu (cond ((null? vars)
289 665c255d 2023-08-04 jrmu (env-loop (enclosing-environment env)))
290 665c255d 2023-08-04 jrmu ((eq? var (car vars))
291 665c255d 2023-08-04 jrmu (car vals))
292 665c255d 2023-08-04 jrmu (else (scan (cdr vars) (cdr vals)))))
293 665c255d 2023-08-04 jrmu (if (eq? env the-empty-environment)
294 665c255d 2023-08-04 jrmu (error "Unbound variable" var)
295 665c255d 2023-08-04 jrmu (let ((frame (first-frame env)))
296 665c255d 2023-08-04 jrmu (scan (frame-variables frame)
297 665c255d 2023-08-04 jrmu (frame-values frame)))))
298 665c255d 2023-08-04 jrmu (env-loop env))
299 665c255d 2023-08-04 jrmu (define (set-variable-value! var val env)
300 665c255d 2023-08-04 jrmu (define (env-loop env)
301 665c255d 2023-08-04 jrmu (define (scan vars vals)
302 665c255d 2023-08-04 jrmu (cond ((null? vars)
303 665c255d 2023-08-04 jrmu (env-loop (enclosing-environment env)))
304 665c255d 2023-08-04 jrmu ((eq? var (car vars))
305 665c255d 2023-08-04 jrmu (set-car! vals val))
306 665c255d 2023-08-04 jrmu (else (scan (cdr vars) (cdr vals)))))
307 665c255d 2023-08-04 jrmu (if (eq? env the-empty-environment)
308 665c255d 2023-08-04 jrmu (error "Unbound variable -- SET!" var)
309 665c255d 2023-08-04 jrmu (let ((frame (first-frame env)))
310 665c255d 2023-08-04 jrmu (scan (frame-variables frame)
311 665c255d 2023-08-04 jrmu (frame-values frame)))))
312 665c255d 2023-08-04 jrmu (env-loop env))
313 665c255d 2023-08-04 jrmu (define (define-variable! var val env)
314 665c255d 2023-08-04 jrmu (let ((frame (first-frame env)))
315 665c255d 2023-08-04 jrmu (define (scan vars vals)
316 665c255d 2023-08-04 jrmu (cond ((null? vars)
317 665c255d 2023-08-04 jrmu (add-binding-to-frame! var val frame))
318 665c255d 2023-08-04 jrmu ((eq? var (car vars))
319 665c255d 2023-08-04 jrmu (set-car! vals val))
320 665c255d 2023-08-04 jrmu (else (scan (cdr vars) (cdr vals)))))
321 665c255d 2023-08-04 jrmu (scan (frame-variables frame)
322 665c255d 2023-08-04 jrmu (frame-values frame))))
324 665c255d 2023-08-04 jrmu ;; primitives
325 665c255d 2023-08-04 jrmu (define (primitive-procedure? proc)
326 665c255d 2023-08-04 jrmu (tagged-list? proc 'primitive))
327 665c255d 2023-08-04 jrmu (define (primitive-implementation proc) (cadr proc))
328 665c255d 2023-08-04 jrmu (define primitive-procedures
329 665c255d 2023-08-04 jrmu (list (list 'car car)
330 665c255d 2023-08-04 jrmu (list 'cdr cdr)
331 665c255d 2023-08-04 jrmu (list 'caar caar)
332 665c255d 2023-08-04 jrmu (list 'cadr cadr)
333 665c255d 2023-08-04 jrmu (list 'cddr cddr)
334 665c255d 2023-08-04 jrmu (list 'cons cons)
335 665c255d 2023-08-04 jrmu (list 'null? null?)
336 665c255d 2023-08-04 jrmu (list '* *)
337 665c255d 2023-08-04 jrmu (list '/ /)
338 665c255d 2023-08-04 jrmu (list '+ +)
339 665c255d 2023-08-04 jrmu (list '- -)
340 665c255d 2023-08-04 jrmu (list '= =)
341 665c255d 2023-08-04 jrmu (list '< <)
342 665c255d 2023-08-04 jrmu (list '> >)
343 665c255d 2023-08-04 jrmu (list '<= <=)
344 665c255d 2023-08-04 jrmu (list '>= >=)
345 665c255d 2023-08-04 jrmu (list 'remainder remainder)
346 665c255d 2023-08-04 jrmu (list 'eq? eq?)
347 665c255d 2023-08-04 jrmu (list 'equal? equal?)
348 665c255d 2023-08-04 jrmu (list 'display display)))
349 665c255d 2023-08-04 jrmu (define (primitive-procedure-names)
351 665c255d 2023-08-04 jrmu primitive-procedures))
352 665c255d 2023-08-04 jrmu (define (primitive-procedure-objects)
353 665c255d 2023-08-04 jrmu (map (lambda (proc) (list 'primitive (cadr proc)))
354 665c255d 2023-08-04 jrmu primitive-procedures))
355 665c255d 2023-08-04 jrmu (define (apply-primitive-procedure proc args)
356 665c255d 2023-08-04 jrmu (apply-in-underlying-scheme
357 665c255d 2023-08-04 jrmu (primitive-implementation proc) args))
359 665c255d 2023-08-04 jrmu ;; driver-loop
360 665c255d 2023-08-04 jrmu (define input-prompt ";;; M-Eval input:")
361 665c255d 2023-08-04 jrmu (define output-prompt ";;; M-Eval value:")
362 665c255d 2023-08-04 jrmu (define (driver-loop)
363 665c255d 2023-08-04 jrmu (prompt-for-input input-prompt)
364 665c255d 2023-08-04 jrmu (let ((input (read)))
365 665c255d 2023-08-04 jrmu (let ((output (eval input the-global-environment)))
366 665c255d 2023-08-04 jrmu (announce-output output-prompt)
367 665c255d 2023-08-04 jrmu (user-print output)))
368 665c255d 2023-08-04 jrmu (driver-loop))
369 665c255d 2023-08-04 jrmu (define (prompt-for-input string)
370 665c255d 2023-08-04 jrmu (newline) (newline) (display string) (newline))
372 665c255d 2023-08-04 jrmu (define (announce-output string)
373 665c255d 2023-08-04 jrmu (newline) (display string) (newline))
374 665c255d 2023-08-04 jrmu (define (user-print object)
375 665c255d 2023-08-04 jrmu (if (compound-procedure? object)
376 665c255d 2023-08-04 jrmu (display (list 'compound-procedure
377 665c255d 2023-08-04 jrmu (procedure-parameters object)
378 665c255d 2023-08-04 jrmu (procedure-body object)
379 665c255d 2023-08-04 jrmu '<procedure-env>))
380 665c255d 2023-08-04 jrmu (display object)))
381 665c255d 2023-08-04 jrmu (define (setup-environment)
382 665c255d 2023-08-04 jrmu (let ((initial-env
383 665c255d 2023-08-04 jrmu (extend-environment (primitive-procedure-names)
384 665c255d 2023-08-04 jrmu (primitive-procedure-objects)
385 665c255d 2023-08-04 jrmu the-empty-environment)))
386 665c255d 2023-08-04 jrmu (define-variable! 'true true initial-env)
387 665c255d 2023-08-04 jrmu (define-variable! 'false false initial-env)
388 665c255d 2023-08-04 jrmu initial-env))
389 665c255d 2023-08-04 jrmu (define the-global-environment (setup-environment))
391 665c255d 2023-08-04 jrmu ;; auxiliary
392 665c255d 2023-08-04 jrmu (define (test-case actual expected)
394 665c255d 2023-08-04 jrmu (display "Actual: ")
395 665c255d 2023-08-04 jrmu (display actual)
397 665c255d 2023-08-04 jrmu (display "Expected: ")
398 665c255d 2023-08-04 jrmu (display expected)
400 665c255d 2023-08-04 jrmu (define (geval exp) ;; eval globally
401 665c255d 2023-08-04 jrmu (eval exp the-global-environment))
402 665c255d 2023-08-04 jrmu (define (test-eval exp expected)
403 665c255d 2023-08-04 jrmu (test-case (geval exp) expected))
406 665c255d 2023-08-04 jrmu ;; Exercise 4.8. ``Named let'' is a variant of let that has the form
408 665c255d 2023-08-04 jrmu ;; (let <var> <bindings> <body>)
410 665c255d 2023-08-04 jrmu ;; The <bindings> and <body> are just as in ordinary let, except that <var> is bound within <body> to a procedure whose body is <body> and whose parameters are the variables in the <bindings>. Thus, one can repeatedly execute the <body> by invoking the procedure named <var>. For example, the iterative Fibonacci procedure (section 1.2.2) can be rewritten using named let as follows:
412 665c255d 2023-08-04 jrmu ;; (let fib-iter ((a 1)
414 665c255d 2023-08-04 jrmu ;; (count n))
415 665c255d 2023-08-04 jrmu ;; (if (= count 0)
417 665c255d 2023-08-04 jrmu ;; (fib-iter (+ a b) a (- count 1))))
420 665c255d 2023-08-04 jrmu ;; test-suite
422 665c255d 2023-08-04 jrmu ;; procedure definitions
425 665c255d 2023-08-04 jrmu '(define (assoc key records)
426 665c255d 2023-08-04 jrmu (cond ((null? records) false)
427 665c255d 2023-08-04 jrmu ((equal? key (caar records)) (car records))
428 665c255d 2023-08-04 jrmu (else (assoc key (cdr records))))))
431 665c255d 2023-08-04 jrmu '(define (map proc list)
432 665c255d 2023-08-04 jrmu (if (null? list)
434 665c255d 2023-08-04 jrmu (cons (proc (car list))
435 665c255d 2023-08-04 jrmu (map proc (cdr list))))))
438 665c255d 2023-08-04 jrmu '(define (accumulate op initial sequence)
439 665c255d 2023-08-04 jrmu (if (null? sequence)
441 665c255d 2023-08-04 jrmu (op (car sequence)
442 665c255d 2023-08-04 jrmu (accumulate op initial (cdr sequence))))))
444 665c255d 2023-08-04 jrmu ;; all special forms
445 665c255d 2023-08-04 jrmu (test-eval '(begin 5 6) 6)
446 665c255d 2023-08-04 jrmu (test-eval '10 10)
447 665c255d 2023-08-04 jrmu (geval '(define x 3))
448 665c255d 2023-08-04 jrmu (test-eval 'x 3)
449 665c255d 2023-08-04 jrmu (test-eval '(set! x -25) 'ok)
450 665c255d 2023-08-04 jrmu (test-eval 'x -25)
451 665c255d 2023-08-04 jrmu (geval '(define z (lambda (x y) (+ x (* x y)))))
452 665c255d 2023-08-04 jrmu (test-eval '(z 3 4) 15)
453 665c255d 2023-08-04 jrmu (test-eval '(cond ((= x -2) 'x=-2)
454 665c255d 2023-08-04 jrmu ((= x -25) 'x=-25)
455 665c255d 2023-08-04 jrmu (else 'failed))
457 665c255d 2023-08-04 jrmu (test-eval '(if true false true) false)
459 665c255d 2023-08-04 jrmu '(let ((x 4) (y 7))
460 665c255d 2023-08-04 jrmu (+ x y (* x y)))
461 665c255d 2023-08-04 jrmu (+ 4 7 (* 4 7)))
465 665c255d 2023-08-04 jrmu (geval '(define x (+ 3 8)))
466 665c255d 2023-08-04 jrmu (test-eval '(and 0 true x) 11)
467 665c255d 2023-08-04 jrmu (test-eval '(and 0 true x false) false)
468 665c255d 2023-08-04 jrmu (test-eval '(and 0 true x (set! x -2) false) false)
469 665c255d 2023-08-04 jrmu (test-eval 'x -2)
470 665c255d 2023-08-04 jrmu (test-eval '(and 0 true x false (set! x -5)) false)
471 665c255d 2023-08-04 jrmu (test-eval 'x -2)
472 665c255d 2023-08-04 jrmu (test-eval '(or false (set! x 25)) 'ok)
473 665c255d 2023-08-04 jrmu (test-eval 'x 25)
474 665c255d 2023-08-04 jrmu (test-eval '(or (set! x 2) (set! x 4)) 'ok)
475 665c255d 2023-08-04 jrmu (test-eval 'x 2)
476 665c255d 2023-08-04 jrmu (test-eval '(or false (set! x 25) true false) 'ok)
477 665c255d 2023-08-04 jrmu (test-eval 'x 25)
478 665c255d 2023-08-04 jrmu (test-eval '(or ((lambda (x) x) 5)) 5)
479 665c255d 2023-08-04 jrmu (test-eval '(or (begin (set! x (+ x 1)) x)) 26)
485 665c255d 2023-08-04 jrmu '(cond ((assoc 'b '((a 1) (b 2))) => cadr)
486 665c255d 2023-08-04 jrmu (else false))
490 665c255d 2023-08-04 jrmu '(cond ((= 3 4) 'not-true)
491 665c255d 2023-08-04 jrmu ((= (* 2 4) 3) 'also-false)
492 665c255d 2023-08-04 jrmu ((map (lambda (x)
493 665c255d 2023-08-04 jrmu (* x (+ x 1)))
494 665c255d 2023-08-04 jrmu '(2 4 1 9))
496 665c255d 2023-08-04 jrmu (lambda (x)
497 665c255d 2023-08-04 jrmu (accumulate + 0 x)))
498 665c255d 2023-08-04 jrmu (else 'never-reach))
500 665c255d 2023-08-04 jrmu ;; '(6 20 2 90)
503 665c255d 2023-08-04 jrmu ;; procedure definition and application
505 665c255d 2023-08-04 jrmu '(define (factorial n)
506 665c255d 2023-08-04 jrmu (if (= n 0)
508 665c255d 2023-08-04 jrmu (* n (factorial (- n 1))))))
509 665c255d 2023-08-04 jrmu (test-eval '(factorial 5) 120)
514 665c255d 2023-08-04 jrmu '(map (lambda (x)
515 665c255d 2023-08-04 jrmu (* x (+ x 1)))
516 665c255d 2023-08-04 jrmu '(2 1 4 2 8 3))
517 665c255d 2023-08-04 jrmu '(6 2 20 6 72 12))
518 665c255d 2023-08-04 jrmu ;; accumulate
521 665c255d 2023-08-04 jrmu '(accumulate + 0 '(1 2 3 4 5))
524 665c255d 2023-08-04 jrmu ;; make-let
526 665c255d 2023-08-04 jrmu (make-let '(x y) '(3 5) '((+ x y)))
533 665c255d 2023-08-04 jrmu '(let ((x 3))
537 665c255d 2023-08-04 jrmu '(let ((x 3)
542 665c255d 2023-08-04 jrmu '(let ((x 3)
544 665c255d 2023-08-04 jrmu (+ (let ((x (+ y 2))
548 665c255d 2023-08-04 jrmu (+ (* 4 3) 3 2))
550 665c255d 2023-08-04 jrmu '(let ((x 6)
551 665c255d 2023-08-04 jrmu (y (let ((x 2))
553 665c255d 2023-08-04 jrmu (z (let ((a (* 3 2)))
562 665c255d 2023-08-04 jrmu '(let* ((x 3)
563 665c255d 2023-08-04 jrmu (y (+ x 2))
564 665c255d 2023-08-04 jrmu (z (+ x y 5)))
573 665c255d 2023-08-04 jrmu '(let* ((x 3))
574 665c255d 2023-08-04 jrmu (let* ((y 5))
579 665c255d 2023-08-04 jrmu '(let* ((x 3)
580 665c255d 2023-08-04 jrmu (y (+ x 1)))
581 665c255d 2023-08-04 jrmu (+ (let* ((x (+ y 2))
585 665c255d 2023-08-04 jrmu (+ (* 6 6) 3 4))
587 665c255d 2023-08-04 jrmu '(let* ((x 6)
588 665c255d 2023-08-04 jrmu (y (let* ((x 2)
589 665c255d 2023-08-04 jrmu (a (let* ((x (* 3 x)))
592 665c255d 2023-08-04 jrmu (z (+ x y)))
596 665c255d 2023-08-04 jrmu ;; named-let
599 665c255d 2023-08-04 jrmu '(let eight ()
605 665c255d 2023-08-04 jrmu '(let loop ((count 0))
606 665c255d 2023-08-04 jrmu (if (= 100 count)
608 665c255d 2023-08-04 jrmu (loop (+ count 1))))
611 665c255d 2023-08-04 jrmu '(define (prime? x)
612 665c255d 2023-08-04 jrmu (let prime-iter ((i 2))
613 665c255d 2023-08-04 jrmu (cond ((> (* i i) x) true)
614 665c255d 2023-08-04 jrmu ((= (remainder x i) 0) false)
615 665c255d 2023-08-04 jrmu (else (prime-iter (+ i 1)))))))
617 665c255d 2023-08-04 jrmu '(let primes ((x 2)
619 665c255d 2023-08-04 jrmu (cond ((= n 0) '())
620 665c255d 2023-08-04 jrmu ((prime? x)
622 665c255d 2023-08-04 jrmu (primes (+ x 1) (- n 1))))
623 665c255d 2023-08-04 jrmu (else (primes (+ x 1) n))))
624 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))
627 665c255d 2023-08-04 jrmu '(define (fib n)
628 665c255d 2023-08-04 jrmu (let fib-iter ((a 1)
631 665c255d 2023-08-04 jrmu (if (= count 0)
633 665c255d 2023-08-04 jrmu (fib-iter (+ a b) a (- count 1))))))
634 665c255d 2023-08-04 jrmu (test-eval '(fib 19) 4181)
