subtraction negate single argument

src/kiss/Prelude.hx

@@ -103,6 +103,10 @@ class Prelude {
     public static var add:Function = makeVarArgsWithArrayCheck(_add, "+");
 
     static function _subtract(values:Array<Dynamic>):Dynamic {
+        // with one argument, just negate:
+        if (values.length == 1)
+            return -values[0];
+
         var difference:Float = values[0];
         for (value in values.slice(1))
             difference -= value;

src/test/cases/BasicTestCase.hx

@@ -72,11 +72,11 @@ class BasicTestCase extends Test {
         Assert.equals(6, BasicTestCase.mySum);
     }
 
-    function testVariadicSubtract() {
-        Assert.equals(-2, BasicTestCase.myDifference);
+    function testSubtraction() {
+        _testSubtraction();
     }
 
-    function testVariadicMultiply() {
+    function testMultiplication() {
         _testMultiplication();
     }
 

src/test/cases/BasicTestCase.kiss

@@ -46,10 +46,11 @@
 (function _testCollect []
     (Assert.equals "[0,1,2]" (Std.string (collect (range 3)))))
 
-// Variadic math uses haxe's Lambda.fold under the hood
 (var mySum (+ 1 2 3))
 
-(var myDifference (- 5 4 3))
+(function _testSubtraction []
+    (Assert.equals -2 (- 5 4 3))
+    (Assert.equals -2 (- 2)))
 
 (function _testMultiplication [] 
     (Assert.equals 60 (* 2 5 6))