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-> (clj)
(source)macro
(-> x & forms)
Threads the expr through the forms. Inserts x as the
second item in the first form, making a list of it if it is not a
list already. If there are more forms, inserts the first form as the
second item in second form, etc.
Examples
clojure
(ns clojure.test-clojure.reducers
(:require [clojure.core.reducers :as r]
[clojure.test.generative :refer (defspec)]
[clojure.data.generators :as gen])
(:use clojure.test))
(defmacro defequivtest
;; f is the core fn, r is the reducers equivalent, rt is the reducible ->
;; coll transformer
[name [f r rt] fns]
`(deftest ~name
(let [c# (range -100 1000)]
(doseq [fn# ~fns]
(is (= (~f fn# c#)
(~rt (~r fn# c#))))))))
(deftest test-mapcat-obeys-reduced
(is (= [1 "0" 2 "1" 3]
(->> (concat (range 100) (lazy-seq (throw (Exception. "Too eager"))))
(r/mapcat (juxt inc str))
(r/take 5)
(into [])))))
clojure
(deftest division
(is (= clojure.core// /))
(binding [*ns* *ns*]
(eval '(do (ns foo
(:require [clojure.core :as bar])
(:use [clojure.test]))
(is (= clojure.core// bar//))))))
(deftest Instants
(testing "Instants are read as java.util.Date by default"
(is (= java.util.Date (class #inst "2010-11-12T13:14:15.666"))))
(let [s "#inst \"2010-11-12T13:14:15.666-06:00\""]
(binding [*data-readers* {'inst read-instant-date}]
(testing "read-instant-date produces java.util.Date"
(is (= java.util.Date (class (read-string s)))))
(testing "java.util.Date instants round-trips"
(is (= (-> s read-string)
(-> s read-string pr-str read-string))))
(testing "java.util.Date instants round-trip throughout the year"
(doseq [month (range 1 13) day (range 1 29) hour (range 1 23)]
(let [s (format "#inst \"2010-%02d-%02dT%02d:14:15.666-06:00\"" month day hour)]
(is (= (-> s read-string)
(-> s read-string pr-str read-string))))))
(testing "java.util.Date handling DST in time zones"
(let [dtz (TimeZone/getDefault)]
(try
;; A timezone with DST in effect during 2010-11-12
(TimeZone/setDefault (TimeZone/getTimeZone "Australia/Sydney"))
(is (= (-> s read-string)
(-> s read-string pr-str read-string)))
(finally (TimeZone/setDefault dtz)))))
(testing "java.util.Date should always print in UTC"
(let [d (read-string s)
pstr (print-str d)
len (.length pstr)]
(is (= (subs pstr (- len 7)) "-00:00\"")))))
(binding [*data-readers* {'inst read-instant-calendar}]
(testing "read-instant-calendar produces java.util.Calendar"
(is (instance? java.util.Calendar (read-string s))))
(testing "java.util.Calendar round-trips"
(is (= (-> s read-string)
(-> s read-string pr-str read-string))))
(testing "java.util.Calendar remembers timezone in literal"
(is (= "#inst \"2010-11-12T13:14:15.666-06:00\""
(-> s read-string pr-str)))
(is (= (-> s read-string)
(-> s read-string pr-str read-string))))
(testing "java.util.Calendar preserves milliseconds"
(is (= 666 (-> s read-string
(.get java.util.Calendar/MILLISECOND)))))))
(let [s "#inst \"2010-11-12T13:14:15.123456789\""
s2 "#inst \"2010-11-12T13:14:15.123\""
s3 "#inst \"2010-11-12T13:14:15.123456789123\""]
(binding [*data-readers* {'inst read-instant-timestamp}]
(testing "read-instant-timestamp produces java.sql.Timestamp"
(is (= java.sql.Timestamp (class (read-string s)))))
(testing "java.sql.Timestamp preserves nanoseconds"
(is (= 123456789 (-> s read-string .getNanos)))
(is (= 123456789 (-> s read-string pr-str read-string .getNanos)))
;; truncate at nanos for s3
(is (= 123456789 (-> s3 read-string pr-str read-string .getNanos))))
(testing "java.sql.Timestamp should compare nanos"
(is (= (read-string s) (read-string s3)))
(is (not= (read-string s) (read-string s2)))))
(binding [*data-readers* {'inst read-instant-date}]
(testing "read-instant-date should truncate at milliseconds"
(is (= (read-string s) (read-string s2) (read-string s3))))))
(let [s "#inst \"2010-11-12T03:14:15.123+05:00\""
s2 "#inst \"2010-11-11T22:14:15.123Z\""]
(binding [*data-readers* {'inst read-instant-date}]
(testing "read-instant-date should convert to UTC"
(is (= (read-string s) (read-string s2)))))
(binding [*data-readers* {'inst read-instant-timestamp}]
(testing "read-instant-timestamp should convert to UTC"
(is (= (read-string s) (read-string s2)))))
(binding [*data-readers* {'inst read-instant-calendar}]
(testing "read-instant-calendar should preserve timezone"
(is (not= (read-string s) (read-string s2)))))))
(defn roundtrip
"Print an object and read it back. Returns rather than throws
any exceptions."
[o]
(binding [*print-length* nil
*print-dup* nil
*print-level* nil]
(try
(-> o pr-str read-string)
(catch Throwable t t))))
(defn roundtrip-dup
"Print an object with print-dup and read it back.
Returns rather than throws any exceptions."
[o]
(binding [*print-length* nil
*print-dup* true
*print-level* nil]
(try
(-> o pr-str read-string)
(catch Throwable t t))))
(defn str->lnpr
[s]
(-> s (java.io.StringReader.) (clojure.lang.LineNumberingPushbackReader.)))
(deftest test-read+string
(let [[r s] (read+string (str->lnpr "[:foo 100]"))]
(is (= [:foo 100] r))
(is (= "[:foo 100]" s)))
(let [[r s] (read+string {:read-cond :allow :features #{:y}} (str->lnpr "#?(:x :foo :y :bar)"))]
(is (= :bar r))
(is (= "#?(:x :foo :y :bar)" s))))
(deftest t-Explicit-line-column-numbers
(is (= {:line 42 :column 99}
(-> "^{:line 42 :column 99} (1 2)" read-string meta (select-keys [:line :column]))))
(are [l c s] (= {:line l :column c} (-> s str->lnpr read meta (select-keys [:line :column])))
42 99 "^{:line 42 :column 99} (1 2)"
1 99 "^{:column 99} (1 2)")
(eval (-> "^{:line 42 :column 99} (defn explicit-line-numbering [])" str->lnpr read))
(is (= {:line 42 :column 99}
(-> 'explicit-line-numbering resolve meta (select-keys [:line :column])))))