Capitalization effect example

Purpose of this effect is to create very simple example that would
be easy to compose in a very obvious way.

examples/src/Capitalize.hs

@@ -0,0 +1,22 @@
+{-# LANGUAGE DataKinds #-}
+{-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE GADTs #-}
+{-# LANGUAGE TypeOperators #-}
+module Capitalize where
+
+import Data.Char (toUpper)
+
+import Control.Monad.Freer
+import Control.Monad.Freer.Internal
+
+data Capitalize v where
+    Capitalize :: String -> Capitalize String
+
+capitalize :: Member Capitalize r => String -> Eff r String
+capitalize = send . Capitalize
+
+runCapitalizeM :: Eff (Capitalize ': r) w -> Eff r w
+runCapitalizeM (Val x) = return x
+runCapitalizeM (E u q) = case decomp u of
+    Right (Capitalize s) -> runCapitalizeM (qApp q (map toUpper s))
+    Left u'              -> E u' (tsingleton (\s -> runCapitalizeM (qApp q s)))

freer-effects.cabal

@@ -88,7 +88,8 @@ executable freer-examples
   hs-source-dirs:       examples/src
   main-is:              Main.hs
   other-modules:
-      Common
+      Capitalize
+    , Common
     , Coroutine
     , Cut
     , Fresh