Introduce a context manager for compiler.returnable

Signed-off-by: Julien Danjou <julien@danjou.info>

hy/compiler.py

@@ -33,7 +33,7 @@ from hy.models.list import HyList
 from hy.models.dict import HyDict
 from hy.models.keyword import HyKeyword
 
-from hy.util import flatten_literal_list, str_type
+from hy.util import flatten_literal_list, str_type, temporary_attribute_value
 
 from collections import defaultdict
 import codecs
@@ -129,6 +129,9 @@ class HyASTCompiler(object):
         self.anon_fn_count = 0
         self.imports = defaultdict(list)
 
+    def being_returnable(self, v):
+        return temporary_attribute_value(self, "returnable", v)
+
     def compile(self, tree):
         try:
             for _type in _compile_table:
@@ -951,9 +954,7 @@ class HyASTCompiler(object):
     @builds("foreach")
     @checkargs(min=1)
     def compile_for_expression(self, expression):
-        ret_status = self.returnable
+        with self.being_returnable(False):
-        self.returnable = False
-
             expression.pop(0)  # for
             name, iterable = expression.pop(0)
             target = self._storeize(self.compile_symbol(name))
@@ -963,7 +964,8 @@ class HyASTCompiler(object):
             if expression and expression[-1][0] == HySymbol("else"):
                 else_expr = expression.pop()
                 if len(else_expr) > 2:
-                raise HyTypeError(else_expr,
+                    raise HyTypeError(
+                        else_expr,
                         "`else' statement in `foreach' is too long")
                 elif len(else_expr) == 2:
                     orelse = self._code_branch(
@@ -981,7 +983,6 @@ class HyASTCompiler(object):
                               expression.start_column),
                           orelse=orelse)
 
-        self.returnable = ret_status
         return ret
 
     @builds("while")
@@ -1012,22 +1013,20 @@ class HyASTCompiler(object):
     def compile_fn_expression(self, expression):
         expression.pop(0)  # fn
 
-        ret_status = self.returnable
-
         self.anon_fn_count += 1
         name = "_hy_anon_fn_%d" % (self.anon_fn_count)
         sig = expression.pop(0)
 
         body = []
         if expression != []:
-            self.returnable = True
+            with self.being_returnable(True):
                 tailop = self.compile(expression.pop(-1))
-            self.returnable = False
+            with self.being_returnable(False):
                 for el in expression:
                     body.append(self.compile(el))
             body.append(tailop)
 
-        self.returnable = True
+        with self.being_returnable(True):
             body = self._code_branch(body,
                                      expression.start_line,
                                      expression.start_column)
@@ -1052,7 +1051,6 @@ class HyASTCompiler(object):
                 body=body,
                 decorator_list=[])
 
-        self.returnable = ret_status
         return ret
 
     @builds(HyInteger)

hy/util.py

@@ -1,4 +1,5 @@
 # Copyright (c) 2013 Paul Tagliamonte <paultag@debian.org>
+# Copyright (c) 2013 Julien Danjou <julien@danjou.info>
 #
 # Permission is hereby granted, free of charge, to any person obtaining a
 # copy of this software and associated documentation files (the "Software"),
@@ -18,6 +19,7 @@
 # FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 # DEALINGS IN THE SOFTWARE.
 
+import contextlib
 import sys
 
 
@@ -27,6 +29,15 @@ else:
     str_type = unicode
 
 
+@contextlib.contextmanager
+def temporary_attribute_value(obj, attribute, value):
+    """Temporarily switch an object attribute value to another value."""
+    original_value = getattr(obj, attribute)
+    setattr(obj, attribute, value)
+    yield
+    setattr(obj, attribute, original_value)
+
+
 def flatten_literal_list(entry):
     for e in entry:
         if type(e) == list:

tests/test_util.py

@@ -0,0 +1,13 @@
+from hy import util
+
+
+def test_temporary_attribute_value():
+    class O(object):
+        def __init__(self):
+            self.foobar = 0
+
+    o = O()
+
+    with util.temporary_attribute_value(o, "foobar", 42):
+        assert o.foobar == 42
+    assert o.foobar == 0