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authorGeoff Liu <g@geoffliu.me>2015-03-16 14:25:46 -0600
committerGeoff Liu <g@geoffliu.me>2015-03-16 14:25:46 -0600
commit366fe47ffa32d257fdbb703d8ae25f6078450db5 (patch)
treeaa6e69071c1755a9dc4384c394f32018016f4429 /racket.html.markdown
parent752279248e4950b5b702896edefec7af4f7ca001 (diff)
parenta6ea67e733d9ecede6c2d29d42a983ae4ffb4506 (diff)
Merge remote-tracking branch 'upstream/master'
Diffstat (limited to 'racket.html.markdown')
-rw-r--r--racket.html.markdown48
1 files changed, 41 insertions, 7 deletions
diff --git a/racket.html.markdown b/racket.html.markdown
index 6abc8759..e345db8b 100644
--- a/racket.html.markdown
+++ b/racket.html.markdown
@@ -7,6 +7,7 @@ contributors:
- ["Eli Barzilay", "https://github.com/elibarzilay"]
- ["Gustavo Schmidt", "https://github.com/gustavoschmidt"]
- ["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.
@@ -282,16 +283,49 @@ m ; => '#hash((b . 2) (a . 1) (c . 3)) <-- no `d'
;; for numbers use `='
(= 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
+(let ([x (list 3)] [y (list 3)])
+ (eq? x y)) ; => #f — not the same list in memory!
+
+(let* ([x (list 3)] [y x])
+ (eq? x y)) ; => #t, since x and y now point to the same stuff
+
+(eq? 'yes 'yes) ; => #t
+(eq? 'yes 'no) ; => #f
+
+(eq? 3 3) ; => #t — be careful here
+ ; It’s 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
-;; for collections use `equal?'
-(equal? (list 'a 'b) (list 'a 'b)) ; => #t
-(equal? (list 'a 'b) (list 'b 'a)) ; => #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