Add while loops to the compiler

TODO

@@ -9,9 +9,6 @@
 
    + Use (def) to imply global foo
 
- - New Builtins:
-   + While
-
  - New macros:
    + loop
 

hy/compiler.py

@@ -545,6 +545,26 @@ class HyASTCompiler(object):
         self.returnable = ret_status
         return ret
 
+    @builds("while")
+    def compile_while_expression(self, expr):
+        expr.pop(0)  # "while"
+
+        try:
+            test = expr.pop(0)
+        except IndexError:
+            raise TypeError("while expects at least 2 arguments, got 0")
+        test = self.compile(test)
+
+        if not expr:
+            raise TypeError("while expects a body")
+
+        return ast.While(test=test,
+                         body=self._mangle_branch([
+                             self.compile(x) for x in expr]),
+                         orelse=[],
+                         lineno=expr.start_line,
+                         col_offset=expr.start_column)
+
     @builds(HyList)
     def compile_list(self, expr):
         return ast.List(

tests/compilers/test_ast.py

@@ -66,6 +66,29 @@ def test_ast_valid_if():
     hy_compile(tokenize("(if foo bar)"))
 
 
+def test_ast_bad_while_0_arg():
+    "Make sure AST can't compile invalid while"
+    try:
+        hy_compile(tokenize("(while)"))
+        assert False
+    except TypeError:
+        pass
+
+
+def test_ast_bad_while_1_arg():
+    "Make sure AST can't compile invalid while"
+    try:
+        hy_compile(tokenize("(while (true))"))
+        assert False
+    except TypeError:
+        pass
+
+
+def test_ast_valid_while():
+    "Make sure AST can't compile invalid while"
+    hy_compile(tokenize("(while foo bar)"))
+
+
 def test_ast_expression_basics():
     """ Ensure basic AST expression conversion works. """
     code = hy_compile(tokenize("(foo bar)")).body[0]

tests/native_tests/language.hy

@@ -32,6 +32,17 @@
   (assert (= count 150)))
 
 
+(defn test-while-loop []
+  "NATIVE: test while loops?"
+  (setv count 5)
+  (setv fact 1)
+  (while (> count 0)
+    (setv fact (* fact count))
+    (setv count (- count 1)))
+  (assert (= count 0))
+  (assert (= fact 120)))
+
+
 (defn test-in []
   "NATIVE: test in"
   (assert (in "a" ["a" "b" "c" "d"]))