diff options
Diffstat (limited to 'semestr-2/racket/l9/zad4.rkt')
| -rw-r--r-- | semestr-2/racket/l9/zad4.rkt | 202 |
1 files changed, 202 insertions, 0 deletions
diff --git a/semestr-2/racket/l9/zad4.rkt b/semestr-2/racket/l9/zad4.rkt new file mode 100644 index 0000000..7b5e0bc --- /dev/null +++ b/semestr-2/racket/l9/zad4.rkt @@ -0,0 +1,202 @@ +#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)))
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