From 9477dbe667f250ecd23f8fc0d56b942191526421 Mon Sep 17 00:00:00 2001
From: Franciszek Malinka <franciszek.malinka@gmail.com>
Date: Thu, 25 Feb 2021 14:42:55 +0100
Subject: Stare semestry, niepoukladane

---
 Semestr 2/racket/l10z18/solution.bak | 363 +++++++++++++++++++++++++++++++
 Semestr 2/racket/l10z18/solution.rkt | 409 +++++++++++++++++++++++++++++++++++
 2 files changed, 772 insertions(+)
 create mode 100644 Semestr 2/racket/l10z18/solution.bak
 create mode 100644 Semestr 2/racket/l10z18/solution.rkt

(limited to 'Semestr 2/racket/l10z18')

diff --git a/Semestr 2/racket/l10z18/solution.bak b/Semestr 2/racket/l10z18/solution.bak
new file mode 100644
index 0000000..02eb770
--- /dev/null
+++ b/Semestr 2/racket/l10z18/solution.bak	
@@ -0,0 +1,363 @@
+#lang racket
+
+;; Składnia abstrakcyjna
+(struct const (val)                 #:transparent)
+(struct var-expr (name)             #:transparent)
+(struct let-expr (id bound body)    #:transparent)
+(struct letrec-expr (id bound body) #:transparent)
+(struct if-expr  (eb et ef)         #:transparent)
+(struct lambda-expr (arg body)      #:transparent)
+(struct app-expr (fun arg)          #:transparent)
+
+(define (keyword s)
+  (member s '(true false null and or if cond else lambda let letrec)))
+
+(define (expr? e)
+  (match e
+    [(const n)           (or (number? n)
+                             (boolean? n)
+                             (null? n)
+                             (string? n))]
+    [(var-expr id)       (symbol? id)]
+    [(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))]
+    [(lambda-expr x e)   (and (symbol? x)
+                              (expr? e))]
+    [(app-expr ef ea)    (and (expr? ef)
+                              (expr? ea))]
+    [_                   false]))
+
+;; Parsowanie (zacytowane wyrażenie -> składnia abstrakcyjna)
+(define (parse q)
+  (cond
+   [(number? q)     (const q)]
+   [(string? q)     (const q)]
+   [(eq? q 'true)   (const true)]
+   [(eq? q 'false)  (const false)]
+   [(eq? q 'null)   (const null)]
+   [(and (symbol? q)
+         (not (keyword q)))
+    (var-expr q)]
+   [(and (list? q)
+         (= (length q) 3)
+         (eq? (first q) 'let)
+         (list? (second q))
+         (= (length (second q)) 2)
+         (symbol? (first (second q))))
+    (let-expr (first (second q))
+              (parse (second (second q)))
+              (parse (third q)))]
+   [(and (list? q)
+         (= (length q) 3)
+         (eq? (first q) 'letrec)
+         (list? (second q))
+         (= (length (second q)) 2)
+         (symbol? (first (second q))))
+    (letrec-expr (first (second q))
+                 (parse (second (second q)))
+                 (parse (third q)))]
+   [(and (list? q)
+         (= (length q) 4)
+         (eq? (first q) 'if))
+    (if-expr (parse (second q))
+             (parse (third q))
+             (parse (fourth q)))]
+   [(and (list? q)
+         (pair? q)
+         (eq? (first q) 'and))
+    (desugar-and (map parse (cdr q)))]
+   [(and (list? q)
+         (pair? q)
+         (eq? (first q) 'or))
+    (desugar-or (map parse (cdr q)))]
+   [(and (list? q)
+         (>= (length q) 2)
+         (eq? (first q) 'cond))
+    (parse-cond (cdr q))]
+   [(and (list? q)
+         (= (length q) 3)
+         (eq? (first q) 'lambda)
+         (list? (second q))
+         (andmap symbol? (second q))
+         (cons? (second q)))
+    (desugar-lambda (second q) (parse (third q)))]
+   [(and (list? q)
+         (>= (length q) 2))
+    (desugar-app (parse (first q)) (map parse (cdr q)))]
+   [else (error "Unrecognized token:" q)]))
+
+(define (parse-cond qs)
+  (match qs
+    [(list (list 'else q))
+     (parse q)]
+
+    [(list (list q _))
+     (error "Expected 'else' in last branch but found:" q)]
+
+    [(cons (list qb qt) qs)
+     (if-expr (parse qb) (parse qt) (parse-cond qs))]))
+
+(define (desugar-and es)
+  (if (null? es)
+      (const true)
+      (if-expr (car es) (desugar-and (cdr es)) (const false))))
+
+(define (desugar-or es)
+  (if (null? es)
+      (const false)
+      (if-expr (car es) (const true) (desugar-or (cdr es)))))
+
+(define (desugar-lambda xs e)
+  (if (null? xs)
+      e
+      (lambda-expr (car xs) (desugar-lambda (cdr xs) e))))
+
+(define (desugar-app e es)
+  (if (null? es)
+      e
+      (desugar-app (app-expr e (car es)) (cdr es))))
+
+;; Środowiska
+(struct blackhole ())
+(struct environ (xs))
+
+(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)))
+           (let ((v (mcdr (car xs))))
+             (if (blackhole? v)
+                 (error "Jumped into blackhole at" x)
+                 v))]
+          [else (assoc-lookup (cdr xs))]))
+  (assoc-lookup (environ-xs env)))
+(define (env-update! x v env)
+  (define (assoc-update xs)
+    (cond [(null? xs) (error "Unknown identifier" x)]
+          [(eq? x (mcar (car xs)))
+           (set-mcdr! (car xs) v)]
+          [else (assoc-update (cdr xs))]))
+  (assoc-update (environ-xs env)))
+
+;; Domknięcia
+(struct clo (arg body env))
+
+;; Procedury wbudowane, gdzie
+;; proc — Racketowa procedura którą należy uruchomić
+;; args — lista dotychczas dostarczonych argumentów
+;; pnum — liczba brakujących argumentów (> 0)
+;; W ten sposób pozwalamy na częściową aplikację Racketowych procedur
+;; — zauważmy że zawsze znamy pnum, bo w naszym języku arność
+;; procedury jest ustalona z góry
+(struct builtin (proc args pnum) #:transparent)
+
+;; Pomocnicze konstruktory procedur unarnych i binarnych
+(define (builtin/1 p)
+  (builtin (lambda (x) (return (p x))) null 1))
+(define (builtin/2 p)
+  (builtin (lambda (x y) (return (p x y))) null 2))
+
+;; Procedury
+(define (proc? v)
+  (or (and (clo? v)
+           (symbol?  (clo-arg v))
+           (expr?    (clo-body v))
+           (environ? (clo-env v)))
+      (and (builtin? v)
+           (procedure? (builtin-proc v))
+           (andmap value? (builtin-args v))
+           (natural? (builtin-pnum v))
+           (> (builtin-pnum v) 0))))
+
+;; Definicja typu wartości
+(define (value? v)
+  (or (number? v)
+      (boolean? v)
+      (null? v)
+      (string? v)
+      (and (cons? v)
+           (value? (car v))
+           (value? (cdr v)))
+      (proc? v)))
+
+;; Środowisko początkowe (przypisujące procedury wbudowane ich nazwom)
+
+(define start-env
+  (foldl (lambda (p env) (env-add (first p) (second p) env))
+         env-empty
+         `((+        ,(builtin/2 +))
+           (-        ,(builtin/2 -))
+           (*        ,(builtin/2 *))
+           (/        ,(builtin/2 /))
+           (~        ,(builtin/1 -))
+           (<        ,(builtin/2 <))
+           (>        ,(builtin/2 >))
+           (=        ,(builtin/2 =))
+           (<=       ,(builtin/2 <=))
+           (>=       ,(builtin/2 >=))
+           (not      ,(builtin/1 not))
+           (cons     ,(builtin/2 cons))
+           (car      ,(builtin/1 car))
+           (cdr      ,(builtin/1 cdr))
+           (pair?    ,(builtin/1 cons?))
+           (null?    ,(builtin/1 null?))
+           (boolean? ,(builtin/1 boolean?))
+           (number?  ,(builtin/1 number?))
+           (procedure? ,(builtin/1 (lambda (x) (or (clo? x) (builtin? x)))))
+           (string?  ,(builtin/1 string?))
+           (string-= ,(builtin/2 string=?))
+           ;; and so on, and so on
+           )))
+
+;; Efekt
+
+(define (effect-builtin/1 p)
+  (builtin p null 1))
+(define (effect-builtin/2 p)
+  (builtin p null 2))
+
+(define effect-env
+  (foldl (lambda (p env) (env-add (first p) (second p) env))
+         start-env
+         `((choose ,(effect-builtin/2 (lambda (x y) (list x y))))
+           )))
+
+(define (bind c k) (append-map k c)) 
+
+(define (return x) (list x))
+
+;; Ewaluator
+(define (eval-env e env)
+  (match e
+    [(const n)
+     (return n)]
+
+    [(var-expr x)
+     (return (env-lookup x env))]
+
+    [(let-expr x e1 e2)
+     (bind (eval-env e1 env) (lambda (v1)
+       (eval-env e2 (env-add x v1 env))))]
+
+    [(letrec-expr f ef eb)
+     (let ((new-env (env-add f (blackhole) env)))
+     (bind (eval-env ef new-env) (lambda (vf)
+       (env-update! f vf new-env)
+       (eval-env eb new-env))))]
+
+    [(if-expr eb et ef)
+     (bind (eval-env eb env) (lambda (vb) 
+     (match vb
+       [#t   (eval-env et env)]
+       [#f   (eval-env ef env)]
+       [v    (error "Not a boolean:" v)])))]
+
+    [(lambda-expr x e)
+     (return (clo x e env))]
+
+    [(app-expr ef ea)
+     (bind (eval-env ef env) (lambda (vf)
+     (bind (eval-env ea env) (lambda (va)
+       (match vf
+         [(clo x e env)
+          (eval-env e (env-add x va env))]
+         [(builtin p args nm)
+          (if (= nm 1)
+              (apply p (reverse (cons va args)))
+              (return (builtin p (cons va args) (- nm 1))))]
+         [_ (error "Not a function:" vf)])))))]))
+
+(define (eval e)
+  (eval-env e effect-env))
+
+
+;; Przykladowy program
+
+(define PROGRAM
+  '((if (choose true false) (lambda (x) x) (lambda (x) (+ x 1))) (choose 1 2)))
+
+
+;; REPL — interpreter interaktywny (read-eval-print loop)
+
+;; dodajemy składnię na wiązanie zmiennych "na poziomie interpretera"
+;; i komendę wyjścia "exit" ...
+(struct letrec-repl (id expr))
+(struct let-repl (id expr))
+(struct exit-repl ())
+
+;; ... a także rozszerzoną procedurę parsującą te dodatkowe komendy i
+;; prostą obsługę błędów
+(define (parse-repl q)
+  (with-handlers
+      ([exn? (lambda (exn)
+                 (display "Parse error! ")
+                 (displayln (exn-message exn)))])
+    (cond
+     [(eq? q 'exit)   (exit-repl)]
+     [(and (list? q)
+           (= 3 (length q))
+           (eq? (first q) 'let))
+      (let-repl (second q) (parse (third q)))]
+     [(and (list? q)
+           (= 3 (length q))
+           (eq? (first q) 'letrec))
+      (letrec-repl (second q) (parse (third q)))]
+     [else (parse q)])))
+
+;; trochę zamieszania w procedurze eval-repl wynika z rudymentarnej
+;; obsługi błędów: nie chcemy żeby błąd w interpretowanym programie
+;; kończył działanie całego interpretera!
+(define (eval-repl c env continue)
+  (define (eval-with-err e env)
+    (with-handlers
+        ([exn? (lambda (exn)
+                 (display "Error! ")
+                 (displayln (exn-message exn)))])
+      (eval-env e env)))
+  (match c
+    [(exit-repl)
+     (void)]
+
+    [(let-repl x e)
+     (let ((v (eval-with-err e env)))
+       (if (void? v)
+           (continue env)
+           (continue (env-add x v env))))]
+
+    [(letrec-repl f e)
+     (let* ((new-env (env-add f (blackhole) env))
+            (v       (eval-with-err e new-env)))
+       (if (void? v)
+           (continue env)
+           (begin
+             (env-update! f v new-env)
+             (continue new-env))))]
+
+    [_
+     (let ((v (eval-with-err c env)))
+       (unless (void? v)
+         (displayln v))
+       (continue env))]))
+
+;; I w końcu interaktywny interpreter
+(define (repl)
+  (define (go env)
+    (display "FUN > ")
+    (let* ((q (read))
+           (c (parse-repl q)))
+      (if (void? c)
+          (go env)
+          (eval-repl c env go))))
+  (displayln "Welcome to the FUN functional language interpreter!")
+  (go start-env))
\ No newline at end of file
diff --git a/Semestr 2/racket/l10z18/solution.rkt b/Semestr 2/racket/l10z18/solution.rkt
new file mode 100644
index 0000000..7adcea4
--- /dev/null
+++ b/Semestr 2/racket/l10z18/solution.rkt	
@@ -0,0 +1,409 @@
+#lang racket
+
+;; Składnia abstrakcyjna
+(struct const (val)                 #:transparent)
+(struct var-expr (name)             #:transparent)
+(struct let-expr (id bound body)    #:transparent)
+(struct letrec-expr (id bound body) #:transparent)
+(struct if-expr  (eb et ef)         #:transparent)
+(struct lambda-expr (arg body)      #:transparent)
+(struct app-expr (fun arg)          #:transparent)
+
+(provide parse eval norm)
+
+(define (keyword s)
+  (member s '(true false null and or if cond else lambda let letrec)))
+
+(define (expr? e)
+  (match e
+    [(const n)           (or (number? n)
+                             (boolean? n)
+                             (null? n)
+                             (string? n))]
+    [(var-expr id)       (symbol? id)]
+    [(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))]
+    [(lambda-expr x e)   (and (symbol? x)
+                              (expr? e))]
+    [(app-expr ef ea)    (and (expr? ef)
+                              (expr? ea))]
+    [_                   false]))
+
+;; Parsowanie (zacytowane wyrażenie -> składnia abstrakcyjna)
+(define (parse q)
+  (cond
+   [(number? q)     (const q)]
+   [(string? q)     (const q)]
+   [(eq? q 'true)   (const true)]
+   [(eq? q 'false)  (const false)]
+   [(eq? q 'null)   (const null)]
+   [(and (symbol? q)
+         (not (keyword q)))
+    (var-expr q)]
+   [(and (list? q)
+         (= (length q) 3)
+         (eq? (first q) 'let)
+         (list? (second q))
+         (= (length (second q)) 2)
+         (symbol? (first (second q))))
+    (let-expr (first (second q))
+              (parse (second (second q)))
+              (parse (third q)))]
+   [(and (list? q)
+         (= (length q) 3)
+         (eq? (first q) 'letrec)
+         (list? (second q))
+         (= (length (second q)) 2)
+         (symbol? (first (second q))))
+    (letrec-expr (first (second q))
+                 (parse (second (second q)))
+                 (parse (third q)))]
+   [(and (list? q)
+         (= (length q) 4)
+         (eq? (first q) 'if))
+    (if-expr (parse (second q))
+             (parse (third q))
+             (parse (fourth q)))]
+   [(and (list? q)
+         (pair? q)
+         (eq? (first q) 'and))
+    (desugar-and (map parse (cdr q)))]
+   [(and (list? q)
+         (pair? q)
+         (eq? (first q) 'or))
+    (desugar-or (map parse (cdr q)))]
+   [(and (list? q)
+         (>= (length q) 2)
+         (eq? (first q) 'cond))
+    (parse-cond (cdr q))]
+   [(and (list? q)
+         (= (length q) 3)
+         (eq? (first q) 'lambda)
+         (list? (second q))
+         (andmap symbol? (second q))
+         (cons? (second q)))
+    (desugar-lambda (second q) (parse (third q)))]
+   [(and (list? q)
+         (>= (length q) 2))
+    (desugar-app (parse (first q)) (map parse (cdr q)))]
+   [else (error "Unrecognized token:" q)]))
+
+(define (parse-cond qs)
+  (match qs
+    [(list (list 'else q))
+     (parse q)]
+
+    [(list (list q _))
+     (error "Expected 'else' in last branch but found:" q)]
+
+    [(cons (list qb qt) qs)
+     (if-expr (parse qb) (parse qt) (parse-cond qs))]))
+
+(define (desugar-and es)
+  (if (null? es)
+      (const true)
+      (if-expr (car es) (desugar-and (cdr es)) (const false))))
+
+(define (desugar-or es)
+  (if (null? es)
+      (const false)
+      (if-expr (car es) (const true) (desugar-or (cdr es)))))
+
+(define (desugar-lambda xs e)
+  (if (null? xs)
+      e
+      (lambda-expr (car xs) (desugar-lambda (cdr xs) e))))
+
+(define (desugar-app e es)
+  (if (null? es)
+      e
+      (desugar-app (app-expr e (car es)) (cdr es))))
+
+;; Środowiska
+(struct blackhole ())
+(struct environ (xs))
+
+(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)))
+           (let ((v (mcdr (car xs))))
+             (if (blackhole? v)
+                 (error "Jumped into blackhole at" x)
+                 v))]
+          [else (assoc-lookup (cdr xs))]))
+  (assoc-lookup (environ-xs env)))
+(define (env-update! x v env)
+  (define (assoc-update xs)
+    (cond [(null? xs) (error "Unknown identifier" x)]
+          [(eq? x (mcar (car xs)))
+           (set-mcdr! (car xs) v)]
+          [else (assoc-update (cdr xs))]))
+  (assoc-update (environ-xs env)))
+
+;; Domknięcia
+(struct clo (arg body env))
+
+;; Procedury wbudowane, gdzie
+;; proc — Racketowa procedura którą należy uruchomić
+;; args — lista dotychczas dostarczonych argumentów
+;; pnum — liczba brakujących argumentów (> 0)
+;; W ten sposób pozwalamy na częściową aplikację Racketowych procedur
+;; — zauważmy że zawsze znamy pnum, bo w naszym języku arność
+;; procedury jest ustalona z góry
+(struct builtin (proc args pnum) #:transparent)
+
+;; Pomocnicze konstruktory procedur unarnych i binarnych
+(define (builtin/1 p)
+  (builtin (lambda (x) (return (p x))) null 1))
+(define (builtin/2 p)
+  (builtin (lambda (x y) (return (p x y))) null 2))
+
+;; Procedury
+(define (proc? v)
+  (or (and (clo? v)
+           (symbol?  (clo-arg v))
+           (expr?    (clo-body v))
+           (environ? (clo-env v)))
+      (and (builtin? v)
+           (procedure? (builtin-proc v))
+           (andmap value? (builtin-args v))
+           (natural? (builtin-pnum v))
+           (> (builtin-pnum v) 0))))
+
+;; Definicja typu wartości
+(define (value? v)
+  (or (number? v)
+      (boolean? v)
+      (null? v)
+      (string? v)
+      (and (cons? v)
+           (value? (car v))
+           (value? (cdr v)))
+      (proc? v)))
+
+;; Środowisko początkowe (przypisujące procedury wbudowane ich nazwom)
+
+(define start-env
+  (foldl (lambda (p env) (env-add (first p) (second p) env))
+         env-empty
+         `((+        ,(builtin/2 +))
+           (-        ,(builtin/2 -))
+           (*        ,(builtin/2 *))
+           (/        ,(builtin/2 /))
+           (~        ,(builtin/1 -))
+           (<        ,(builtin/2 <))
+           (>        ,(builtin/2 >))
+           (=        ,(builtin/2 =))
+           (<=       ,(builtin/2 <=))
+           (>=       ,(builtin/2 >=))
+           (not      ,(builtin/1 not))
+           (cons     ,(builtin/2 cons))
+           (car      ,(builtin/1 car))
+           (cdr      ,(builtin/1 cdr))
+           (pair?    ,(builtin/1 cons?))
+           (null?    ,(builtin/1 null?))
+           (boolean? ,(builtin/1 boolean?))
+           (number?  ,(builtin/1 number?))
+           (procedure? ,(builtin/1 (lambda (x) (or (clo? x) (builtin? x)))))
+           (string?  ,(builtin/1 string?))
+           (string-= ,(builtin/2 string=?))
+           ;; and so on, and so on
+           )))
+
+;; Efekt
+
+(define (effect-builtin/1 p)
+  (builtin p null 1))
+(define (effect-builtin/2 p)
+  (builtin p null 2))
+(define (effect-builtin/3 p)
+  (builtin p null 3))
+
+
+(define effect-env
+  (foldl (lambda (p env) (env-add (first p) (second p) env))
+         start-env
+         `((flip ,(effect-builtin/3 (lambda (p x y) (list (cons p x) (cons (- 1 p) y)))))
+           (uniform ,(effect-builtin/1 (lambda (x) (let ((l (/ 1 (length x))))
+                                                      (map (lambda (x) (cons l x)) x)))))
+           )))
+
+;; c to lista par (pstwo, wartość)
+;; k to funkcja która przyjmuje wartość i coś z nią robi sobie i zwraca listę par (pstwo, wartość)
+
+(define (bind c k) 
+  (append-map 
+    (lambda (x) (let ((pstwo (car x))
+                      (val (cdr x)))
+                  (map 
+                    (lambda (x) (cons (* pstwo (car x)) (cdr x))) 
+                    (k (cdr x))))) 
+  c))
+                                                   
+(define (return x) (list (cons 1 x)))
+
+;; Ewaluator
+(define (eval-env e env)
+  (match e
+    [(const n)
+     (return n)]
+
+    [(var-expr x)
+     (return (env-lookup x env))]
+
+    [(let-expr x e1 e2)
+     (bind (eval-env e1 env) (lambda (v1)
+       (eval-env e2 (env-add x v1 env))))]
+
+    [(letrec-expr f ef eb)
+     (let ((new-env (env-add f (blackhole) env)))
+     (bind (eval-env ef new-env) (lambda (vf)
+       (env-update! f vf new-env)
+       (eval-env eb new-env))))]
+
+    [(if-expr eb et ef)
+     (bind (eval-env eb env) (lambda (vb) 
+     (match vb
+       [#t   (eval-env et env)]
+       [#f   (eval-env ef env)]
+       [v    (error "Not a boolean:" v)])))]
+
+    [(lambda-expr x e)
+     (return (clo x e env))]
+
+    [(app-expr ef ea)
+     (bind (eval-env ef env) (lambda (vf)
+     (bind (eval-env ea env) (lambda (va)
+       (match vf
+         [(clo x e env)
+          (eval-env e (env-add x va env))]
+         [(builtin p args nm)
+          (if (= nm 1)
+              (apply p (reverse (cons va args)))
+              (return (builtin p (cons va args) (- nm 1))))]
+         [_ (error "Not a function:" vf)])))))]))
+
+(define (eval e)
+  (eval-env e effect-env))
+
+
+;; Przykladowy program
+
+(define PROGRAM
+  '((if (choose true false) (lambda (x) x) (lambda (x) (+ x 1))) (choose 1 2)))
+
+
+;; REPL — interpreter interaktywny (read-eval-print loop)
+
+;; dodajemy składnię na wiązanie zmiennych "na poziomie interpretera"
+;; i komendę wyjścia "exit" ...
+(struct letrec-repl (id expr))
+(struct let-repl (id expr))
+(struct exit-repl ())
+
+;; ... a także rozszerzoną procedurę parsującą te dodatkowe komendy i
+;; prostą obsługę błędów
+(define (parse-repl q)
+  (with-handlers
+      ([exn? (lambda (exn)
+                 (display "Parse error! ")
+                 (displayln (exn-message exn)))])
+    (cond
+     [(eq? q 'exit)   (exit-repl)]
+     [(and (list? q)
+           (= 3 (length q))
+           (eq? (first q) 'let))
+      (let-repl (second q) (parse (third q)))]
+     [(and (list? q)
+           (= 3 (length q))
+           (eq? (first q) 'letrec))
+      (letrec-repl (second q) (parse (third q)))]
+     [else (parse q)])))
+
+;; trochę zamieszania w procedurze eval-repl wynika z rudymentarnej
+;; obsługi błędów: nie chcemy żeby błąd w interpretowanym programie
+;; kończył działanie całego interpretera!
+(define (eval-repl c env continue)
+  (define (eval-with-err e env)
+    (with-handlers
+        ([exn? (lambda (exn)
+                 (display "Error! ")
+                 (displayln (exn-message exn)))])
+      (eval-env e env)))
+  (match c
+    [(exit-repl)
+     (void)]
+
+    [(let-repl x e)
+     (let ((v (eval-with-err e env)))
+       (if (void? v)
+           (continue env)
+           (continue (env-add x v env))))]
+
+    [(letrec-repl f e)
+     (let* ((new-env (env-add f (blackhole) env))
+            (v       (eval-with-err e new-env)))
+       (if (void? v)
+           (continue env)
+           (begin
+             (env-update! f v new-env)
+             (continue new-env))))]
+
+    [_
+     (let ((v (eval-with-err c env)))
+       (unless (void? v)
+         (displayln v))
+       (continue env))]))
+
+;; I w końcu interaktywny interpreter
+(define (repl)
+  (define (go env)
+    (display "FUN > ")
+    (let* ((q (read))
+           (c (parse-repl q)))
+      (if (void? c)
+          (go env)
+          (eval-repl c env go))))
+  (displayln "Welcome to the FUN functional language interpreter!")
+  (go start-env))
+
+
+(define prog '(if (flip 0.3 true false) "wygrana" "przegrana"))
+
+
+(define (norm xs)
+  (define sum (lambda (xs) (foldl + 0 xs)))
+  (define carlist (lambda (xs) (map car xs)))
+  (define (iter xs res)
+    (cond 
+      [(null? xs) res]
+      [(member (cdar xs) (map cdr res)) (iter (cdr xs) res)]
+      [else (let* ((cur (cdar xs))
+                   (pstwa (filter (lambda (x) (equal? (cdr x) cur)) xs)))
+              (iter (cdr xs) (cons (cons (sum (carlist pstwa)) cur) res)))]))
+  (iter xs null))
+        
+
+(define DICE-MANY
+  '(letrec [from-to (lambda (x n)
+                  (cons x 
+                        (if (= x n)
+                        null
+                        (from-to (+ 1 x) n))))]
+   (let    [dice (lambda (x) (uniform (from-to 1 6)))]
+   (letrec [dice-many (lambda (n) (if (= n 0)
+                                      0
+                                      (+ (dice 0) (dice-many (- n 1)))))]
+   (dice-many (dice 0))))))
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