Add argument destructuring

hy/compiler.py

@@ -1934,6 +1934,19 @@ class HyASTCompiler(object):
             raise HyTypeError(expression,
                               "First argument to (fn) must be a list")
         ret, args, defaults, stararg, kwargs = self._parse_lambda_list(arglist)
+        for i, arg in enumerate(args):
+            if isinstance(arg, HyList):
+                # Destructuring argument
+                if not arg:
+                    raise HyTypeError(arglist,
+                                      "Cannot destruct empty list")
+                args[i] = var = HySymbol(self.get_anon_var())
+                expression = HyExpression([
+                    HyExpression([
+                        HyString("setv"), arg, var
+                    ])]
+                ) + expression
+                expression = expression.replace(arg[0])
 
         if PY34:
             # Python 3.4+ requires that args are an ast.arg object, rather

tests/compilers/test_ast.py

@@ -404,6 +404,12 @@ def test_ast_tuple():
     assert type(code) == ast.Tuple
 
 
+def test_argument_destructuring():
+    """ Ensure argument destructuring compilers. """
+    can_compile("(fn [[a b]] (print a b))")
+    cant_compile("(fn [[]] 0)")
+
+
 def test_lambda_list_keywords_rest():
     """ Ensure we can compile functions with lambda list keywords."""
     can_compile("(fn (x &rest xs) (print xs))")

tests/native_tests/language.hy

@@ -1153,3 +1153,8 @@
   (assert
    (= (identify-keywords 1 "bloo" :foo)
       ["other" "other" "keyword"])))
+
+(defn test-argument-destr []
+  "Make sure argument destructuring works"
+  (defn f [[a b] [c]] (, a b c))
+  (assert (= (f [1 2] [3]) (, 1 2 3))))