diff --git a/esphomeyaml/automation.py b/esphomeyaml/automation.py
index a3cb8e3a57..8e73a314ca 100644
--- a/esphomeyaml/automation.py
+++ b/esphomeyaml/automation.py
@@ -10,7 +10,7 @@ from esphomeyaml.core import CORE
 from esphomeyaml.cpp_generator import ArrayInitializer, Pvariable, TemplateArguments, add, \
     get_variable, process_lambda, templatable
 from esphomeyaml.cpp_types import Action, App, Component, PollingComponent, Trigger, \
-    esphomelib_ns, float_, uint32
+    esphomelib_ns, float_, uint32, void, bool_
 from esphomeyaml.util import ServiceRegistry
 
 
@@ -266,7 +266,7 @@ LAMBDA_ACTION_SCHEMA = cv.lambda_
 
 @ACTION_REGISTRY.register(CONF_LAMBDA, LAMBDA_ACTION_SCHEMA)
 def lambda_action_to_code(config, action_id, arg_type, template_arg):
-    for lambda_ in process_lambda(config, [(arg_type, 'x')]):
+    for lambda_ in process_lambda(config, [(arg_type, 'x')], return_type=void):
         yield None
     rhs = LambdaAction.new(template_arg, lambda_)
     type = LambdaAction.template(template_arg)
@@ -278,7 +278,7 @@ LAMBDA_CONDITION_SCHEMA = cv.lambda_
 
 @CONDITION_REGISTRY.register(CONF_LAMBDA, LAMBDA_CONDITION_SCHEMA)
 def lambda_condition_to_code(config, condition_id, arg_type, template_arg):
-    for lambda_ in process_lambda(config, [(arg_type, 'x')]):
+    for lambda_ in process_lambda(config, [(arg_type, 'x')], return_type=bool_):
         yield
     rhs = LambdaCondition.new(template_arg, lambda_)
     type = LambdaCondition.template(template_arg)
diff --git a/esphomeyaml/components/binary_sensor/__init__.py b/esphomeyaml/components/binary_sensor/__init__.py
index 2a3c909c20..6e08acd9d6 100644
--- a/esphomeyaml/components/binary_sensor/__init__.py
+++ b/esphomeyaml/components/binary_sensor/__init__.py
@@ -13,7 +13,8 @@ from esphomeyaml.const import CONF_DELAYED_OFF, CONF_DELAYED_ON, CONF_DEVICE_CLA
 from esphomeyaml.core import CORE
 from esphomeyaml.cpp_generator import process_lambda, ArrayInitializer, add, Pvariable, \
     StructInitializer, get_variable
-from esphomeyaml.cpp_types import esphomelib_ns, Nameable, Trigger, NoArg, Component, App, bool_
+from esphomeyaml.cpp_types import esphomelib_ns, Nameable, Trigger, NoArg, Component, App, bool_, \
+    optional
 from esphomeyaml.py_compat import string_types
 
 DEVICE_CLASSES = [
@@ -207,8 +208,8 @@ def setup_filter(config):
     elif CONF_HEARTBEAT in config:
         yield App.register_component(HeartbeatFilter.new(config[CONF_HEARTBEAT]))
     elif CONF_LAMBDA in config:
-        lambda_ = None
-        for lambda_ in process_lambda(config[CONF_LAMBDA], [(bool_, 'x')]):
+        for lambda_ in process_lambda(config[CONF_LAMBDA], [(bool_, 'x')],
+                                      return_type=optional.template(bool_)):
             yield None
         yield LambdaFilter.new(lambda_)
 
diff --git a/esphomeyaml/components/display/lcd_gpio.py b/esphomeyaml/components/display/lcd_gpio.py
index c0264618ff..c796ed3f28 100644
--- a/esphomeyaml/components/display/lcd_gpio.py
+++ b/esphomeyaml/components/display/lcd_gpio.py
@@ -7,7 +7,7 @@ from esphomeyaml.const import CONF_DATA_PINS, CONF_DIMENSIONS, CONF_ENABLE_PIN,
     CONF_LAMBDA, CONF_RS_PIN, CONF_RW_PIN
 from esphomeyaml.cpp_generator import Pvariable, add, process_lambda
 from esphomeyaml.cpp_helpers import gpio_output_pin_expression, setup_component
-from esphomeyaml.cpp_types import App, PollingComponent
+from esphomeyaml.cpp_types import App, PollingComponent, void
 
 LCDDisplay = display.display_ns.class_('LCDDisplay', PollingComponent)
 LCDDisplayRef = LCDDisplay.operator('ref')
@@ -64,7 +64,8 @@ def to_code(config):
         add(lcd.set_rw_pin(rw))
 
     if CONF_LAMBDA in config:
-        for lambda_ in process_lambda(config[CONF_LAMBDA], [(LCDDisplayRef, 'it')]):
+        for lambda_ in process_lambda(config[CONF_LAMBDA], [(LCDDisplayRef, 'it')],
+                                      return_type=void):
             yield
         add(lcd.set_writer(lambda_))
 
diff --git a/esphomeyaml/components/display/lcd_pcf8574.py b/esphomeyaml/components/display/lcd_pcf8574.py
index f967f259d1..cc3792f992 100644
--- a/esphomeyaml/components/display/lcd_pcf8574.py
+++ b/esphomeyaml/components/display/lcd_pcf8574.py
@@ -7,7 +7,7 @@ import esphomeyaml.config_validation as cv
 from esphomeyaml.const import CONF_ADDRESS, CONF_DIMENSIONS, CONF_ID, CONF_LAMBDA
 from esphomeyaml.cpp_generator import Pvariable, add, process_lambda
 from esphomeyaml.cpp_helpers import setup_component
-from esphomeyaml.cpp_types import App
+from esphomeyaml.cpp_types import App, void
 
 DEPENDENCIES = ['i2c']
 
@@ -28,7 +28,8 @@ def to_code(config):
         add(lcd.set_address(config[CONF_ADDRESS]))
 
     if CONF_LAMBDA in config:
-        for lambda_ in process_lambda(config[CONF_LAMBDA], [(LCDDisplayRef, 'it')]):
+        for lambda_ in process_lambda(config[CONF_LAMBDA], [(LCDDisplayRef, 'it')],
+                                      return_type=void):
             yield
         add(lcd.set_writer(lambda_))
 
diff --git a/esphomeyaml/components/display/max7219.py b/esphomeyaml/components/display/max7219.py
index 7283d5932e..fcca07154b 100644
--- a/esphomeyaml/components/display/max7219.py
+++ b/esphomeyaml/components/display/max7219.py
@@ -8,7 +8,7 @@ from esphomeyaml.const import CONF_CS_PIN, CONF_ID, CONF_INTENSITY, CONF_LAMBDA,
     CONF_SPI_ID
 from esphomeyaml.cpp_generator import Pvariable, add, get_variable, process_lambda
 from esphomeyaml.cpp_helpers import gpio_output_pin_expression, setup_component
-from esphomeyaml.cpp_types import App, PollingComponent
+from esphomeyaml.cpp_types import App, PollingComponent, void
 
 DEPENDENCIES = ['spi']
 
@@ -39,7 +39,8 @@ def to_code(config):
         add(max7219.set_intensity(config[CONF_INTENSITY]))
 
     if CONF_LAMBDA in config:
-        for lambda_ in process_lambda(config[CONF_LAMBDA], [(MAX7219ComponentRef, 'it')]):
+        for lambda_ in process_lambda(config[CONF_LAMBDA], [(MAX7219ComponentRef, 'it')],
+                                      return_type=void):
             yield
         add(max7219.set_writer(lambda_))
 
diff --git a/esphomeyaml/components/display/nextion.py b/esphomeyaml/components/display/nextion.py
index 254a76eddf..4d051c39b6 100644
--- a/esphomeyaml/components/display/nextion.py
+++ b/esphomeyaml/components/display/nextion.py
@@ -4,7 +4,7 @@ import esphomeyaml.config_validation as cv
 from esphomeyaml.const import CONF_ID, CONF_LAMBDA, CONF_UART_ID
 from esphomeyaml.cpp_generator import Pvariable, add, get_variable, process_lambda
 from esphomeyaml.cpp_helpers import setup_component
-from esphomeyaml.cpp_types import App, PollingComponent
+from esphomeyaml.cpp_types import App, PollingComponent, void
 
 DEPENDENCIES = ['uart']
 
@@ -24,7 +24,8 @@ def to_code(config):
     nextion = Pvariable(config[CONF_ID], rhs)
 
     if CONF_LAMBDA in config:
-        for lambda_ in process_lambda(config[CONF_LAMBDA], [(NextionRef, 'it')]):
+        for lambda_ in process_lambda(config[CONF_LAMBDA], [(NextionRef, 'it')],
+                                      return_type=void):
             yield
         add(nextion.set_writer(lambda_))
 
diff --git a/esphomeyaml/components/display/ssd1306_i2c.py b/esphomeyaml/components/display/ssd1306_i2c.py
index 27a77018b5..966ecdc844 100644
--- a/esphomeyaml/components/display/ssd1306_i2c.py
+++ b/esphomeyaml/components/display/ssd1306_i2c.py
@@ -8,7 +8,7 @@ from esphomeyaml.const import CONF_ADDRESS, CONF_EXTERNAL_VCC, CONF_ID, CONF_LAM
     CONF_RESET_PIN
 from esphomeyaml.cpp_generator import Pvariable, add, process_lambda
 from esphomeyaml.cpp_helpers import gpio_output_pin_expression, setup_component
-from esphomeyaml.cpp_types import App
+from esphomeyaml.cpp_types import App, void
 
 DEPENDENCIES = ['i2c']
 
@@ -37,7 +37,7 @@ def to_code(config):
         add(ssd.set_address(config[CONF_ADDRESS]))
     if CONF_LAMBDA in config:
         for lambda_ in process_lambda(config[CONF_LAMBDA],
-                                      [(display.DisplayBufferRef, 'it')]):
+                                      [(display.DisplayBufferRef, 'it')], return_type=void):
             yield
         add(ssd.set_writer(lambda_))
 
diff --git a/esphomeyaml/components/display/ssd1306_spi.py b/esphomeyaml/components/display/ssd1306_spi.py
index 34e24ba8b2..54cd05995b 100644
--- a/esphomeyaml/components/display/ssd1306_spi.py
+++ b/esphomeyaml/components/display/ssd1306_spi.py
@@ -8,7 +8,7 @@ from esphomeyaml.const import CONF_CS_PIN, CONF_DC_PIN, CONF_EXTERNAL_VCC, CONF_
     CONF_MODEL, CONF_RESET_PIN, CONF_SPI_ID
 from esphomeyaml.cpp_generator import Pvariable, add, get_variable, process_lambda
 from esphomeyaml.cpp_helpers import gpio_output_pin_expression, setup_component
-from esphomeyaml.cpp_types import App, PollingComponent
+from esphomeyaml.cpp_types import App, PollingComponent, void
 
 DEPENDENCIES = ['spi']
 
@@ -60,7 +60,7 @@ def to_code(config):
         add(ssd.set_external_vcc(config[CONF_EXTERNAL_VCC]))
     if CONF_LAMBDA in config:
         for lambda_ in process_lambda(config[CONF_LAMBDA],
-                                      [(display.DisplayBufferRef, 'it')]):
+                                      [(display.DisplayBufferRef, 'it')], return_type=void):
             yield
         add(ssd.set_writer(lambda_))
 
diff --git a/esphomeyaml/components/display/waveshare_epaper.py b/esphomeyaml/components/display/waveshare_epaper.py
index 2c0a7ccc79..bfca5bb3fd 100644
--- a/esphomeyaml/components/display/waveshare_epaper.py
+++ b/esphomeyaml/components/display/waveshare_epaper.py
@@ -9,7 +9,7 @@ from esphomeyaml.const import CONF_BUSY_PIN, CONF_CS_PIN, CONF_DC_PIN, CONF_FULL
 from esphomeyaml.cpp_generator import get_variable, Pvariable, process_lambda, add
 from esphomeyaml.cpp_helpers import gpio_output_pin_expression, gpio_input_pin_expression, \
     setup_component
-from esphomeyaml.cpp_types import PollingComponent, App
+from esphomeyaml.cpp_types import PollingComponent, App, void
 
 DEPENDENCIES = ['spi']
 
@@ -71,7 +71,8 @@ def to_code(config):
         raise NotImplementedError()
 
     if CONF_LAMBDA in config:
-        for lambda_ in process_lambda(config[CONF_LAMBDA], [(display.DisplayBufferRef, 'it')]):
+        for lambda_ in process_lambda(config[CONF_LAMBDA], [(display.DisplayBufferRef, 'it')],
+                                      return_type=void):
             yield
         add(epaper.set_writer(lambda_))
     if CONF_RESET_PIN in config:
diff --git a/esphomeyaml/components/light/__init__.py b/esphomeyaml/components/light/__init__.py
index 79cbfdd177..0997d1fd5b 100644
--- a/esphomeyaml/components/light/__init__.py
+++ b/esphomeyaml/components/light/__init__.py
@@ -14,7 +14,7 @@ from esphomeyaml.core import CORE
 from esphomeyaml.cpp_generator import process_lambda, Pvariable, add, StructInitializer, \
     ArrayInitializer, get_variable, templatable
 from esphomeyaml.cpp_types import esphomelib_ns, Application, Component, Nameable, Action, uint32, \
-    float_, std_string
+    float_, std_string, void
 
 PLATFORM_SCHEMA = cv.PLATFORM_SCHEMA.extend({
 
@@ -255,7 +255,7 @@ def build_effect(full_config):
     key, config = next(iter(full_config.items()))
     if key == CONF_LAMBDA:
         lambda_ = None
-        for lambda_ in process_lambda(config[CONF_LAMBDA], []):
+        for lambda_ in process_lambda(config[CONF_LAMBDA], [], return_type=void):
             yield None
         yield LambdaLightEffect.new(config[CONF_NAME], lambda_, config[CONF_UPDATE_INTERVAL])
     elif key == CONF_RANDOM:
@@ -291,7 +291,7 @@ def build_effect(full_config):
         yield effect
     elif key == CONF_ADDRESSABLE_LAMBDA:
         args = [(AddressableLightRef, 'it')]
-        for lambda_ in process_lambda(config[CONF_LAMBDA], args):
+        for lambda_ in process_lambda(config[CONF_LAMBDA], args, return_type=void):
             yield None
         yield AddressableLambdaLightEffect.new(config[CONF_NAME], lambda_,
                                                config[CONF_UPDATE_INTERVAL])
diff --git a/esphomeyaml/components/logger.py b/esphomeyaml/components/logger.py
index 59a86807af..ad713a4c2d 100644
--- a/esphomeyaml/components/logger.py
+++ b/esphomeyaml/components/logger.py
@@ -8,7 +8,7 @@ from esphomeyaml.const import CONF_ARGS, CONF_BAUD_RATE, CONF_FORMAT, CONF_ID, C
     CONF_LOGS, CONF_TAG, CONF_TX_BUFFER_SIZE
 from esphomeyaml.core import EsphomeyamlError, Lambda, CORE
 from esphomeyaml.cpp_generator import Pvariable, RawExpression, add, process_lambda, statement
-from esphomeyaml.cpp_types import App, Component, esphomelib_ns, global_ns
+from esphomeyaml.cpp_types import App, Component, esphomelib_ns, global_ns, void
 
 from esphomeyaml.py_compat import text_type
 
@@ -146,7 +146,7 @@ def logger_log_action_to_code(config, action_id, arg_type, template_arg):
 
     text = text_type(statement(esp_log(config[CONF_TAG], config[CONF_FORMAT], *args)))
 
-    for lambda_ in process_lambda(Lambda(text), [(arg_type, 'x')]):
+    for lambda_ in process_lambda(Lambda(text), [(arg_type, 'x')], return_type=void):
         yield None
     rhs = LambdaAction.new(template_arg, lambda_)
     type = LambdaAction.template(template_arg)
diff --git a/esphomeyaml/components/mqtt.py b/esphomeyaml/components/mqtt.py
index 4276cadcab..36afaa9f62 100644
--- a/esphomeyaml/components/mqtt.py
+++ b/esphomeyaml/components/mqtt.py
@@ -18,7 +18,7 @@ from esphomeyaml.core import EsphomeyamlError
 from esphomeyaml.cpp_generator import ArrayInitializer, Pvariable, RawExpression, \
     StructInitializer, TemplateArguments, add, process_lambda, templatable
 from esphomeyaml.cpp_types import Action, App, Component, JsonObjectConstRef, JsonObjectRef, \
-    Trigger, bool_, esphomelib_ns, optional, std_string, uint8
+    Trigger, bool_, esphomelib_ns, optional, std_string, uint8, void
 
 
 def validate_message_just_topic(value):
@@ -237,7 +237,8 @@ def mqtt_publish_json_action_to_code(config, action_id, arg_type, template_arg):
         yield None
     add(action.set_topic(template_))
 
-    for lambda_ in process_lambda(config[CONF_PAYLOAD], [(arg_type, 'x'), (JsonObjectRef, 'root')]):
+    for lambda_ in process_lambda(config[CONF_PAYLOAD], [(arg_type, 'x'), (JsonObjectRef, 'root')],
+                                  return_type=void):
         yield None
     add(action.set_payload(lambda_))
     if CONF_QOS in config:
diff --git a/esphomeyaml/components/sensor/__init__.py b/esphomeyaml/components/sensor/__init__.py
index 4e72835c96..5f8f52152f 100644
--- a/esphomeyaml/components/sensor/__init__.py
+++ b/esphomeyaml/components/sensor/__init__.py
@@ -16,7 +16,7 @@ from esphomeyaml.core import CORE
 from esphomeyaml.cpp_generator import ArrayInitializer, Pvariable, add, process_lambda, \
     templatable, get_variable
 from esphomeyaml.cpp_types import App, Component, Nameable, PollingComponent, Trigger, \
-    esphomelib_ns, float_
+    esphomelib_ns, float_, optional
 
 PLATFORM_SCHEMA = cv.PLATFORM_SCHEMA.extend({
 
@@ -136,7 +136,8 @@ def setup_filter(config):
         yield ExponentialMovingAverageFilter.new(conf[CONF_ALPHA], conf[CONF_SEND_EVERY])
     elif CONF_LAMBDA in config:
         lambda_ = None
-        for lambda_ in process_lambda(config[CONF_LAMBDA], [(float_, 'x')]):
+        for lambda_ in process_lambda(config[CONF_LAMBDA], [(float_, 'x')],
+                                      return_type=optional.template(float_)):
             yield None
         yield LambdaFilter.new(lambda_)
     elif CONF_THROTTLE in config:
diff --git a/esphomeyaml/cpp_types.py b/esphomeyaml/cpp_types.py
index d441094657..c07e0c6436 100644
--- a/esphomeyaml/cpp_types.py
+++ b/esphomeyaml/cpp_types.py
@@ -1,6 +1,7 @@
 from esphomeyaml.cpp_generator import MockObj
 
 global_ns = MockObj('', '')
+void = global_ns.namespace('void')
 float_ = global_ns.namespace('float')
 bool_ = global_ns.namespace('bool')
 std_ns = global_ns.namespace('std')