add a raise_ helper function which is slightly more convenient than six.reraise

Author: radix

effect/__init__.py

@@ -9,7 +9,7 @@
 
 from __future__ import absolute_import
 
-from ._base import Effect, perform, NoPerformerFoundError, catch
+from ._base import Effect, perform, NoPerformerFoundError, catch, raise_
 from ._sync import (
     NotSynchronousError,
     sync_perform,
@@ -28,5 +28,5 @@
     "Constant", "Error", "FirstError", "Func",
     "base_dispatcher",
     "TypeDispatcher", "ComposedDispatcher",
-    "catch",
+    "catch", "raise_",
 ]

effect/_base.py

@@ -167,7 +167,7 @@ def _perform(bouncer, effect):
 
 def catch(exc_type, callable):
     """
-    A helper for handling errors of a specific type.
+    A helper for handling errors of a specific type::
 
         eff.on(error=catch(SpecificException,
                            lambda exc_info: "got an error!"))
@@ -180,3 +180,17 @@ def catcher(exc_info):
             return callable(exc_info)
         six.reraise(*exc_info)
     return catcher
+
+
+def raise_(exception, tb=None):
+    """Simple convenience function to allow raising exceptions from lambdas.
+
+    This is slightly more convenient than ``six.reraise`` because it takes an
+    exception instance instead of needing the type separate from the instance.
+
+    :param exception: An exception *instance* (not an exception type).
+
+    - ``raise_(exc)`` is the same as ``raise exc``.
+    - ``raise_(exc, tb)`` is the same as ``raise type(exc), exc, tb``.
+    """
+    six.reraise(type(exception), exception, tb)