Change xor to binary function

xor with more than two input parameters is not well defined and people
have different expectations on how it should behave. Avoid confusion by
sticking with two parameters only.

docs/language/api.rst

@@ -1516,10 +1516,9 @@ xor
 
 .. versionadded:: 0.12.0
 
-``xor`` is used in logical expressions to perform exclusive or. It takes at
-least two parameters. It returns ``True`` if exactly one of the parameters
-evaluates to ``True``. In all other cases ``False`` is returned. Example
-usage:
+``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
 
@@ -1529,7 +1528,7 @@ usage:
     => (xor True True)
     False
 
-    => (xor [] [] [0])
+    => (xor [] [0])
     True
 
 

hy/core/language.hy

@@ -425,6 +425,11 @@
         (hyify (. value __name__))
         (catch [] (string value))))))
 
+(defn xor [a b]
+  "Perform exclusive or between two parameters"
+  (or (and a (not b))
+      (and b (not a))))
+
 (def *exports* '[Botsbuildbots
                  butlast calling-module-name coll? cons cons? cycle
                  dec distinct disassemble drop drop-last drop-while empty? even?
@@ -434,4 +439,5 @@
                  keyword? last list* macroexpand macroexpand-1 map merge-with
                  name neg? nil? none? nth numeric? odd? pos? range read read-str
                  remove repeat repeatedly rest reduce second some string string?
-                 symbol? take take-nth take-while zero? zip zip_longest zipwith])
+                 symbol? take take-nth take-while xor zero? zip zip_longest
+                 zipwith])

hy/core/macros.hy

@@ -237,8 +237,3 @@
   (let [[decorators (slice expr nil -1)]
         [fndef (get expr -1)]]
     `(with-decorator ~@decorators ~fndef)))
-
-(defmacro xor [&rest args]
-  "perform exclusive or comparison between all arguments"
-  (when (< (len args) 2) (macro-error nil "xor requires at least two arguments."))
-  `(= (reduce (fn [a b] (if b (inc a) a)) ~args 0) 1))

tests/native_tests/language.hy

@@ -817,18 +817,10 @@
   "NATIVE: test the xor macro"
   (let [[xor-both-true (xor true true)]
         [xor-both-false (xor false false)]
-        [xor-true-false (xor true false)]
-        [xor-one-true (xor false true false)]
-        [xor-one-false (xor true false true)]
-        [xor-all-true (xor true true true)]
-        [xor-all-false (xor false false false)]]
+        [xor-true-false (xor true false)]]
     (assert (= xor-both-true false))
     (assert (= xor-both-false false))
-    (assert (= xor-true-false true))
-    (assert (= xor-one-true true))
-    (assert (= xor-one-false false))
-    (assert (= xor-all-true false))
-    (assert (= xor-all-false false))))
+    (assert (= xor-true-false true))))
 
 (defn test-if-return-branching []
   "NATIVE: test the if return branching"