Merge pull request #872 from tuturto/xor

Add exclusive or logical operator

docs/language/api.rst

@@ -1489,6 +1489,27 @@ expands to:
    Section :ref:`using-gensym`
 
 
+xor
+---
+
+.. versionadded:: 0.12.0
+
+``xor`` is used in logical expressions to perform exclusive or. It takes two
+parameters. It returns ``True`` if only of the parameters is ``True``. In all
+other cases ``False`` is returned. Example usage:
+
+.. code-block:: clj
+
+    => (xor True False)
+    True
+
+    => (xor True True)
+    False
+
+    => (xor [] [0])
+    True
+
+
 yield
 -----
 

hy/core/language.hy

@@ -463,6 +463,11 @@
         (hyify (. value __name__))
         (except [] (string value))))))
 
+(defn xor [a b]
+  "Perform exclusive or between two parameters"
+  (or (and a (not b))
+      (and b (not a))))
+
 (def *exports*
   '[*map accumulate butlast calling-module-name chain coll? combinations
     compress cons cons? count cycle dec distinct disassemble drop drop-last
@@ -472,4 +477,4 @@
     last list* macroexpand macroexpand-1 map merge-with multicombinations name
     neg? nil? none? nth numeric? odd? partition permutations pos? product range
     read read-str remove repeat repeatedly rest reduce second some string
-    string? symbol? take take-nth take-while tee zero? zip zip-longest])
+    string? symbol? take take-nth take-while xor tee zero? zip zip-longest])

tests/native_tests/language.hy

@@ -927,6 +927,15 @@
   (assert (= a 1)))
 
 
+(defn test-xor []
+  "NATIVE: test the xor macro"
+  (let [xor-both-true (xor true true)
+        xor-both-false (xor false false)
+        xor-true-false (xor true false)]
+    (assert (= xor-both-true false))
+    (assert (= xor-both-false false))
+    (assert (= xor-true-false true))))
+
 (defn test-if-return-branching []
   "NATIVE: test the if return branching"
                                 ; thanks, algernon