Making the controllers more linear

Basically, the idea of `(oneBranch <> secondBranch)` instead of

```
do
x <- foo
case x of
  ...
```

src/AFRP/Diagram.hs

@@ -1,3 +1,4 @@
+{-# LANGUAGE OverloadedStrings #-}
 module AFRP.Diagram where
 import Data.Text (Text)
 import qualified Text.Printf as Text
@@ -23,22 +24,26 @@ emptyDiagram :: DiagramC
 emptyDiagram r = r Empty
 
 
-renderF :: DiagramF (Maybe String) -> Maybe String
+renderF :: DiagramF (Maybe T.Text) -> Maybe T.Text
 renderF = \case
   Empty -> Nothing
-  Step n x -> Just $ T.unpack n <> maybe "" (Text.printf "( %s )") x
+  Step n x -> Just $ n <> T.pack (maybe "" (Text.printf "( %s )") x)
   Then (Just a) (Just b) -> Just $ a <> " -> " <> b
   Then (Just a) _ -> Just a
   Then _ b -> b
-  Both (Just a) (Just b) -> Just $ Text.printf "(%s, %s)" a b
+  Both (Just a) (Just b) -> Just $ T.pack $ Text.printf "(%s, %s)" a b
   Both (Just a) _ -> Just a
   Both _ b -> b
-  Branch (Just a) (Just b) -> Just $ Text.printf "(%s || %s)" a b
-  Branch (Just a) Nothing -> Just $ Text.printf "(%s || <skip>)" a
+  Branch (Just a) (Just b) -> Just $ T.pack $ Text.printf "(%s || %s)" a b
+  -- I'm leaving this here. This would be technically more correct (showing
+  -- the empty branch, ie. the full if-then-else, but often we care about a
+  -- more simplistic `when` style structure
+  -- Branch (Just a) Nothing -> Just $ T.pack $ Text.printf "(%s || <skip>)" a
+  Branch (Just a) Nothing -> Just $ T.pack $ Text.printf "%s" a
   Branch _ b -> b
-  Merge (Just a) (Just b) -> Just $ Text.printf "(%s, %s)" a b
+  Merge (Just a) (Just b) -> Just $ T.pack $ Text.printf "(%s, %s)" a b
   Merge (Just a) _ -> Just a
   Merge _ b -> b
-  Compose (Just a) (Just b) -> Just $ Text.printf "(%s, %s)" a b
+  Compose (Just a) (Just b) -> Just $ T.pack $ Text.printf "(%s, %s)" a b
   Compose (Just a) _ -> Just a
   Compose _ b -> b