Let setv take pairs of arguments (ref. #844)

docs/language/api.rst

@@ -334,6 +334,18 @@ For example:
     => (counter [1 2 3 4 5 2 3] 2)
     2
 
+They can be used to assign multiple variables at once:
+
+.. code-block:: hy
+
+    => (setv a 1 b 2)
+    (1L, 2L)
+    => a
+    1L
+    => b
+    2L
+    =>
+
 
 defclass
 --------

hy/compiler.py

@@ -1903,11 +1903,29 @@ class HyASTCompiler(object):
 
     @builds("def")
     @builds("setv")
-    @checkargs(2)
+    @checkargs(min=2)
     def compile_def_expression(self, expression):
-        return self._compile_assign(expression[1], expression[2],
-                                    expression.start_line,
-                                    expression.start_column)
+        expression.pop(0)
+        if len(expression) == 2:
+            return self._compile_assign(expression[0], expression[1],
+                                        expression.start_line,
+                                        expression.start_column)
+        elif len(expression) % 2 != 0:
+            raise HyTypeError(expression,
+                              "setv needs an even number of arguments")
+        else:
+            result = Result()
+            exprs = []
+            for tgt, target in zip(expression[::2], expression[1::2]):
+                item = self._compile_assign(tgt, target,
+                                            tgt.start_line, tgt.start_column)
+                result += item
+                exprs.append(item.force_expr)
+
+            result += ast.Tuple(elts=exprs, lineno=expression.start_line,
+                                col_offset=expression.start_column,
+                                ctx=ast.Load())
+            return result
 
     def _compile_assign(self, name, result,
                         start_line, start_column):

tests/native_tests/language.hy

@@ -58,6 +58,18 @@
   (try (eval '(defn lambda [] (print "hello")))
        (catch [e [TypeError]] (assert (in "Can't assign to a builtin" (str e))))))
 
+
+(defn test-setv-pairs []
+  "NATIVE: test that setv works on pairs of arguments"
+  (assert (= (setv a 1 b 2) (, 1 2)))
+  (assert (= a 1))
+  (assert (= b 2))
+  (setv y 0 x 1 y x)
+  (assert y)
+  (try (eval '(setv a 1 b))
+       (catch [e [TypeError]] (assert (in "setv needs an even number of arguments" (str e))))))
+
+
 (defn test-fn-corner-cases []
   "NATIVE: tests that fn/defn handles corner cases gracefully"
   (try (eval '(fn "foo"))