Keyan Zhang 2015-03-13 14:04:20 -04:00
parent 5148227611
commit 8f904480c0

View File

@ -7,6 +7,7 @@ contributors:
- ["Eli Barzilay", "https://github.com/elibarzilay"] - ["Eli Barzilay", "https://github.com/elibarzilay"]
- ["Gustavo Schmidt", "https://github.com/gustavoschmidt"] - ["Gustavo Schmidt", "https://github.com/gustavoschmidt"]
- ["Duong H. Nguyen", "https://github.com/cmpitg"] - ["Duong H. Nguyen", "https://github.com/cmpitg"]
- ["Keyan Zhang", "https://github.com/keyanzhang"]
--- ---
Racket is a general purpose, multi-paradigm programming language in the Lisp/Scheme family. Racket is a general purpose, multi-paradigm programming language in the Lisp/Scheme family.
@ -282,16 +283,49 @@ m ; => '#hash((b . 2) (a . 1) (c . 3)) <-- no `d'
;; for numbers use `=' ;; for numbers use `='
(= 3 3.0) ; => #t (= 3 3.0) ; => #t
(= 2 1) ; => #f (= 2 1) ; => #f
;; `eq?' returns #t if 2 arguments refer to the same object (in memory),
;; #f otherwise.
;; In other words, it's a simple pointer comparison.
(eq? '() '()) ; => #t, since there exists only one empty list in memory
(let ([x '()] [y '()])
(eq? x y)) ; => #t, same as above
;; for object identity use `eq?'
(eq? 3 3) ; => #t
(eq? 3 3.0) ; => #f
(eq? (list 3) (list 3)) ; => #f (eq? (list 3) (list 3)) ; => #f
(let ([x (list 3)] [y (list 3)])
(eq? x y)) ; => #f — not the same list in memory!
;; for collections use `equal?' (let* ([x (list 3)] [y x])
(equal? (list 'a 'b) (list 'a 'b)) ; => #t (eq? x y)) ; => #t, since x and y now point to the same stuff
(equal? (list 'a 'b) (list 'b 'a)) ; => #f
(eq? 'yes 'yes) ; => #t
(eq? 'yes 'no) ; => #f
(eq? 3 3) ; => #t — be careful here
; Its better to use `=' for number comparisons.
(eq? 3 3.0) ; => #f
(eq? (expt 2 100) (expt 2 100)) ; => #f
(eq? (integer->char 955) (integer->char 955)) ; => #f
(eq? (string-append "foo" "bar") (string-append "foo" "bar")) ; => #f
;; `eqv?' supports the comparison of number and character datatypes.
;; for other datatypes, `eqv?' and `eq?' return the same result.
(eqv? 3 3.0) ; => #f
(eqv? (expt 2 100) (expt 2 100)) ; => #t
(eqv? (integer->char 955) (integer->char 955)) ; => #t
(eqv? (string-append "foo" "bar") (string-append "foo" "bar")) ; => #f
;; `equal?' supports the comparison of the following datatypes:
;; strings, byte strings, pairs, mutable pairs, vectors, boxes,
;; hash tables, and inspectable structures.
;; for other datatypes, `equal?' and `eqv?' return the same result.
(equal? 3 3.0) ; => #f
(equal? (string-append "foo" "bar") (string-append "foo" "bar")) ; => #t
(equal? (list 3) (list 3)) ; => #t
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; 5. Control Flow ;; 5. Control Flow