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#lang racket
; Do let-env.rkt dodajemy wartosci boolowskie
;
; 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 if-expr (eb et ef) #: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))]
[(if-expr eb et ef) ; <--------------------------------------- !!!
(and (expr? eb) (expr? et) (expr? ef))]
[_ false]))
(define (parse q)
(cond
[(number? q) (const q)]
[(eq? q 'true) (const true)] ; <---------------------------- !!!
[(eq? q 'false) (const false)] ; <---------------------------- !!!
[(symbol? q) (var-expr 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) 4) (eq? (first q) 'if)) ; <--- !!!
(if-expr (parse (second q))
(parse (third q))
(parse (fourth q)))]
[(and (list? q) (eq? (length q) 3) (symbol? (first q)))
(binop (first q)
(parse (second q))
(parse (third q)))]))
(define (test-parse) (parse '(let [x (+ 2 2)] (+ x 1))))
; ---------- ;
; Srodowiska ;
; ---------- ;
(struct environ (xs))
(define env-empty (environ null))
(define (env-add x v env)
(environ (cons (cons x v) (environ-xs env))))
(define (env-lookup x env)
(define (assoc-lookup xs)
(cond [(null? xs) (error "Unknown identifier" x)]
[(eq? x (car (car xs))) (cdr (car xs))]
[else (assoc-lookup (cdr xs))]))
(assoc-lookup (environ-xs env)))
; --------- ;
; Ewaluacja ;
; --------- ;
(define (value? v)
(or (number? v) (boolean? v)))
(define (op->proc op)
(match op ['+ +] ['- -] ['* *] ['/ /] ['% modulo] ; <----------- !!!
['= =] ['> >] ['>= >=] ['< <] ['<= <=]
['and (lambda (x y) (and x y))]
['or (lambda (x y) (or x y))]))
(define (eval-env e env)
(match e
[(const n) n]
[(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))]
[(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))]))
(define (eval e) (eval-env e env-empty))
(define program
'(if (or (< (% 123 10) 5)
true)
(+ 2 3)
(/ 2 0)))
(define (test-eval) (eval (parse program)))
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