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| -rw-r--r-- | clojure.html.markdown | 25 |
1 files changed, 25 insertions, 0 deletions
diff --git a/clojure.html.markdown b/clojure.html.markdown index a125d18f..58e835c9 100644 --- a/clojure.html.markdown +++ b/clojure.html.markdown @@ -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 ;;;;;;;;;;;;;;; |