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authorEli Barzilay <eli@barzilay.org>2013-07-16 01:55:29 -0400
committerEli Barzilay <eli@barzilay.org>2013-07-16 01:55:29 -0400
commit6af5c957d039eb4712092dcaf1e531ae4e9a35f9 (patch)
tree05ead1d45c61009e5efc248f904755eeff31c31a /racket.html.markdown
parent5d952fb6dab4989454c7e2e43fac664180817df8 (diff)
Clarify functional data structures.
Note that `set-add' is functional, clarify immutable hashes, add mutable hash examples to contrast.
Diffstat (limited to 'racket.html.markdown')
-rw-r--r--racket.html.markdown25
1 files changed, 18 insertions, 7 deletions
diff --git a/racket.html.markdown b/racket.html.markdown
index 21769e90..7ae9dad0 100644
--- a/racket.html.markdown
+++ b/racket.html.markdown
@@ -97,7 +97,7 @@ some-var ; => 5
;; You can also use unicode characters
(define ⊆ subset?)
-(⊆ (set 3 2) (set 1 2 3)); => #t
+(⊆ (set 3 2) (set 1 2 3)) ; => #t
;; Accessing a previously unassigned variable is an exception
; x ; => x: undefined ...
@@ -147,11 +147,12 @@ my-pet ; => #<dog>
;;; Sets
-;; create a set from a list
+;; Create a set from a list
(list->set '(1 2 3 1 2 3 3 2 1 3 2 1)) ; => (set 1 2 3)
;; Add a member with `set-add'
-(set-add (set 1 2 3) 4); => (set 1 2 3 4)
+;; (Functional: returns the extended set rather than mutate the input)
+(set-add (set 1 2 3) 4) ; => (set 1 2 3 4)
;; Remove one with `set-remove'
(set-remove (set 1 2 3) 1) ; => (set 2 3)
@@ -162,7 +163,7 @@ my-pet ; => #<dog>
;;; Hashes
-;; Create an immutable hash table (There are also mutables ones)
+;; Create an immutable hash table (mutable example below)
(define m (hash 'a 1 'b 2 'c 3))
;; Retrieve a value
@@ -174,16 +175,26 @@ my-pet ; => #<dog>
;; You can provide a default value for missing keys
(hash-ref m 'd 0) ; => 0
-;; Use `hash-set' to extend a hash table
+;; Use `hash-set' to extend an immutable hash table
+;; (Returns the extended hash instdead of mutating it)
(define m2 (hash-set m 'd 4))
m2 ; => '#hash((b . 2) (a . 1) (d . 4) (c . 3))
;; Remember, these hashes are immutable!
-m ; => '#hash((b . 2) (a . 1) (c . 3))
+m ; => '#hash((b . 2) (a . 1) (c . 3)) <-- no `d'
-;; Use `hash-remove' to remove keys
+;; Use `hash-remove' to remove keys (functional too)
(hash-remove m 'a) ; => '#hash((b . 2) (c . 3))
+;; Create an empty mutable hash table and manipulate it
+(define m3 (make-hash))
+(hash-set! m3 'a 1)
+(hash-set! m3 'b 2)
+(hash-set! m3 'c 3)
+(hash-ref m3 'a) ; => 1
+(hash-ref m3 'd 0) ; => 0
+(hash-remove! m3 'a)
+
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; 3. Functions
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;