blob: 7b5e0bc93fc01266b8792614fee9c5adf98822be (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
|
#lang racket
; Do fun.rkt dodajemy rekurencyjne let-y
;
; Miejsca, ktore sie zmienily oznaczone sa przez !!!
; --------- ;
; Wyrazenia ;
; --------- ;
(struct const (val) #:transparent)
(struct binop (op l r) #:transparent)
(struct var-expr (id) #:transparent)
(struct let-expr (id e1 e2) #:transparent)
(struct letrec-expr (id e1 e2) #:transparent) ; <----------------- !!!
(struct if-expr (eb et ef) #:transparent)
(struct cons-expr (e1 e2) #:transparent)
(struct car-expr (e) #:transparent)
(struct cdr-expr (e) #:transparent)
(struct null-expr () #:transparent)
(struct null?-expr (e) #:transparent)
(struct app (f e) #:transparent)
(struct lam (id e) #:transparent)
(struct citation (q) #:transparent)
(define (expr? e)
(match e
[(const n) (or (number? n) (boolean? n))]
[(binop op l r) (and (symbol? op) (expr? l) (expr? r))]
[(var-expr x) (symbol? x)]
[(let-expr x e1 e2)
(and (symbol? x) (expr? e1) (expr? e2))]
[(letrec-expr x e1 e2) ; <------------------------------------ !!!
(and (symbol? x) (expr? e1) (expr? e2))]
[(if-expr eb et ef)
(and (expr? eb) (expr? et) (expr? ef))]
[(cons-expr e1 e2) (and (expr? e1) (expr? e2))]
[(car-expr e) (expr? e)]
[(cdr-expr e) (expr? e)]
[(null-expr) true]
[(null?-expr e) (expr? e)]
[(app f e) (and (expr? f) (expr? e))]
[(lam id e) (and (symbol? id) (expr? e))]
[(citation q) true]
[_ false]))
(define (parse q)
(cond
[(number? q) (const q)]
[(eq? q 'true) (const true)]
[(eq? q 'false) (const false)]
[(eq? q 'null) (null-expr)]
[(symbol? q) (var-expr q)]
[(and (list? q) (eq? 'quote (first q))) (citation (second q))]
[(and (list? q) (eq? (length q) 2) (eq? (first q) 'null?))
(null?-expr (parse (second q)))]
[(and (list? q) (eq? (length q) 3) (eq? (first q) 'cons))
(cons-expr (parse (second q))
(parse (third q)))]
[(and (list? q) (eq? (length q) 2) (eq? (first q) 'car))
(car-expr (parse (second q)))]
[(and (list? q) (eq? (length q) 2) (eq? (first q) 'cdr))
(cdr-expr (parse (second q)))]
[(and (list? q) (eq? (length q) 3) (eq? (first q) 'let))
(let-expr (first (second q))
(parse (second (second q)))
(parse (third q)))]
[(and (list? q) (eq? (length q) 3) (eq? (first q) 'letrec)) ; <!!!
(letrec-expr (first (second q))
(parse (second (second q)))
(parse (third q)))]
[(and (list? q) (eq? (length q) 4) (eq? (first q) 'if))
(if-expr (parse (second q))
(parse (third q))
(parse (fourth q)))]
[(and (list? q) (eq? (length q) 3) (eq? (first q) 'lambda))
(parse-lam (second q) (third q))]
[(and (list? q) (pair? q) (not (op->proc (car q))))
(parse-app q)]
[(and (list? q) (eq? (length q) 3) (symbol? (first q)))
(binop (first q)
(parse (second q))
(parse (third q)))]))
(define (parse-app q)
(define (parse-app-accum q acc)
(cond [(= 1 (length q)) (app acc (parse (car q)))]
[else (parse-app-accum (cdr q) (app acc (parse (car q))))]))
(parse-app-accum (cdr q) (parse (car q))))
(define (parse-lam pat e)
(cond [(= 1 (length pat))
(lam (car pat) (parse e))]
[else
(lam (car pat) (parse-lam (cdr pat) e))]))
; ---------- ;
; Srodowiska ;
; ---------- ;
(struct blackhole () #:transparent) ; <------------------------- !!!
(struct environ (xs) #:transparent)
(define env-empty (environ null))
(define (env-add x v env)
(environ (cons (mcons x v) (environ-xs env)))) ; <-------------- !!!
(define (env-lookup x env)
(define (assoc-lookup xs)
(cond [(null? xs) (error "Unknown identifier" x)]
[(eq? x (mcar (car xs))) ; <---------------------------- !!!
(match (mcdr (car xs))
[(blackhole) (error "Stuck forever in a black hole!")]
[x x])]
[else (assoc-lookup (cdr xs))]))
(assoc-lookup (environ-xs env)))
(define (env-update! x v xs) ; <---------------------------------- !!!
(define (assoc-update! xs)
(cond [(null? xs) (error "Unknown identifier" x)]
[(eq? x (mcar (car xs))) (set-mcdr! (car xs) v)]
[else (env-update! x v (cdr xs))]))
(assoc-update! (environ-xs xs)))
; --------- ;
; Ewaluacja ;
; --------- ;
(struct clo (id e env) #:transparent)
(define (value? v)
(or (number? v)
(boolean? v)
(and (pair? v) (value? (car v)) (value? (cdr v)))
(null? v)
(clo? v)
(blackhole? v))) ; <---------------------------------------- !!!
(define (op->proc op)
(match op ['+ +] ['- -] ['* *] ['/ /] ['% modulo]
['= =] ['> >] ['>= >=] ['< <] ['<= <=]
['and (lambda (x y) (and x y))]
['or (lambda (x y) (or x y))]
[_ false]))
(define (eval-env e env)
(match e
[(const n) n]
[(citation q) q]
[(binop op l r) ((op->proc op) (eval-env l env)
(eval-env r env))]
[(let-expr x e1 e2)
(eval-env e2 (env-add x (eval-env e1 env) env))]
[(letrec-expr x e1 e2) ; <------------------------------------ !!!
(let* ([new-env (env-add x (blackhole) env)]
[v (eval-env e1 new-env)])
(begin
(env-update! x v new-env)
(eval-env e2 new-env)))]
[(var-expr x) (env-lookup x env)]
[(if-expr eb et ef) (if (eval-env eb env)
(eval-env et env)
(eval-env ef env))]
[(cons-expr e1 e2) (cons (eval-env e1 env)
(eval-env e2 env))]
[(car-expr e) (car (eval-env e env))]
[(cdr-expr e) (cdr (eval-env e env))]
[(null-expr) null]
[(null?-expr e) (null? (eval-env e env))]
[(lam x e) (clo x e env)]
[(app f e)
(let ([vf (eval-env f env)]
[ve (eval-env e env)])
(match vf [(clo x body fun-env)
(eval-env body (env-add x ve fun-env))]))]))
(define (eval e) (eval-env e env-empty))
(define program
'(letrec
[fact (lambda (n) (if (= n 0) 1 (* n (fact (- n 1)))))]
(letrec
[even-odd
(cons
(lambda (x)
(if (= x 0) true ((cdr even-odd) (- x 1))))
(lambda (x)
(if (= x 0) false ((car even-odd) (- x 1)))))]
(let [even (car even-odd)]
(let [odd (cdr even-odd)]
(even (fact 6)))))))
(define PROGRAM
'(letrec [from-to (lambda (n k)
(if (> n k)
null
(cons n (from-to (+ n 1) k))))]
(letrec [sum (lambda (xs)
(if (null? xs)
0
(+ (car xs) (sum (cdr xs)))))]
(sum (from-to 1 36)))))
(define (test-eval) (eval (parse PROGRAM)))
|