Add zero? predicate to check if an object is zero

AUTHORS

@@ -16,3 +16,4 @@
 * Guillermo Vayá <guivaya@gmail.com>
 * Bob Tolbert <bob@tolbert.org>
 * Ralph Möritz <ralph.moeritz@outlook.com>
+* Josh McLaughlin <josh@phear.cc>

docs/language/core.rst

@@ -270,6 +270,27 @@ Return True if x is greater than zero (0).
    False
 
 
+.. _zero?-fn:
+
+zero?
+----
+
+Usage: ``(zero? x)``
+
+Return True if x is zero (0).
+
+.. code-block:: clojure
+
+   => (zero? 3)
+   False
+
+   => (zero? -2)
+   False
+
+   => (zero? 0)
+   True
+
+
 Sequence Functions
 =======================
 

hy/core/language.hy

@@ -154,7 +154,12 @@
         (yield val)
         (break)))))
 
+(defn zero? [n]
+  "Return true if n is 0"
+  (_numeric_check n)
+  (= n 0))
+
 (def *exports* ["cycle" "dec" "distinct" "drop" "even?" "filter" "inc"
                 "instance?" "iterable?" "iterate" "iterator?" "neg?"
                 "none?" "nth" "numeric?" "odd?" "pos?" "remove" "repeat"
-                "repeatedly" "take" "take_nth" "take_while"])
+                "repeatedly" "take" "take_nth" "take_while" "zero?"])

tests/native_tests/core.hy

@@ -181,6 +181,18 @@
   (try (do (neg? None) (assert False))
        (catch [e [TypeError]] (assert (in "not a number" (str e))))))
 
+(defn test-zero []
+  "NATIVE: testing the zero? function"
+  (assert-false (zero? -2))
+  (assert-false (zero? 1))
+  (assert-true (zero? 0))
+  (try (do (zero? "foo") (assert False))
+       (catch [e [TypeError]] (assert (in "not a number" (str e)))))
+  (try (do (zero? []) (assert False))
+       (catch [e [TypeError]] (assert (in "not a number" (str e)))))
+  (try (do (zero? None) (assert False))
+       (catch [e [TypeError]] (assert (in "not a number" (str e))))))
+
 (defn test-none []
   "NATIVE: testing for `is None`"
   (assert-true (none? None))