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authorC. Bess <cbess@company.com>2015-11-09 17:55:53 -0600
committerC. Bess <cbess@company.com>2015-11-09 17:55:53 -0600
commitdf0992d72c2a28f140e6ff9681c505f36e19249a (patch)
tree508aa3abe4c25b957dca442560d9c95c9b1fc97a /clojure.html.markdown
parentafc5ea14654e0e9cd11c7ef1b672639d12418bad (diff)
parentc460e1fafa0e9b4edc6a5cb35b970bb5cc030a81 (diff)
Merge remote-tracking branch 'adambard/master'
Conflicts: swift.html.markdown
Diffstat (limited to 'clojure.html.markdown')
-rw-r--r--clojure.html.markdown27
1 files changed, 26 insertions, 1 deletions
diff --git a/clojure.html.markdown b/clojure.html.markdown
index 7917ab08..58e835c9 100644
--- a/clojure.html.markdown
+++ b/clojure.html.markdown
@@ -22,7 +22,7 @@ and often automatically.
; Clojure is written in "forms", which are just
; lists of things inside parentheses, separated by whitespace.
;
-; The clojure reader assumes that the first thing is a
+; The clojure reader assumes that the first thing is a
; function or macro to call, and the rest are arguments.
; The first call in a file should be ns, to set the namespace
@@ -264,6 +264,31 @@ keymap ; => {:a 1, :b 2, :c 3}
(print "Saying hello to " name)
(str "Hello " name)) ; => "Hello Urkel" (prints "Saying hello to Urkel")
+
+; Use the threading macros (-> and ->>) to express transformations of
+; data more clearly.
+
+; The "Thread-first" macro (->) inserts into each form the result of
+; the previous, as the first argument (second item)
+(->
+ {:a 1 :b 2}
+ (assoc :c 3) ;=> (assoc {:a 1 :b 2} :c 3)
+ (dissoc :b)) ;=> (dissoc (assoc {:a 1 :b 2} :c 3) :b)
+
+; This expression could be written as:
+; (dissoc (assoc {:a 1 :b 2} :c 3) :b)
+; and evaluates to {:a 1 :c 3}
+
+; The double arrow does the same thing, but inserts the result of
+; each line at the *end* of the form. This is useful for collection
+; operations in particular:
+(->>
+ (range 10)
+ (map inc) ;=> (map inc (range 10)
+ (filter odd?) ;=> (filter odd? (map inc (range 10))
+ (into [])) ;=> (into [] (filter odd? (map inc (range 10)))
+ ; Result: [1 3 5 7 9]
+
; Modules
;;;;;;;;;;;;;;;