More convenient switch and multiSwitch.

1 files changed, 11 insertions, 13 deletions

diff --git a/Spear/Step.hs b/Spear/Step.hs
index e767166..a860247 100644
--- a/Spear/Step.hs
+++ b/Spear/Step.hs
@@ -112,9 +112,11 @@ swhen expectedEvent step = Step $ \elapsed dt state maybeEvent a ->
              in (a', swhen expectedEvent step')
       else (a, swhen expectedEvent step)
 
--- | Construct a step that switches between two steps based on input.
+-- | Construct a step that switches between two steps based on input events.
 --
--- The initial step is the first one.
+-- The current step runs with every 'runStep' even when there are no new events.
+--
+-- The initial step is the identity, 'sid'.
 switch ::
   Eq e =>
   e ->
@@ -122,16 +124,8 @@ switch ::
   e ->
   Step s (Maybe e) a a ->
   Step s (Maybe e) a a
-switch flag1 s1 flag2 s2 = switch' s1 flag1 s1 flag2 s2
+switch = switch' sid
 
-switch' ::
-  Eq e =>
-  Step s (Maybe e) a a ->
-  e ->
-  Step s (Maybe e) a a ->
-  e ->
-  Step s (Maybe e) a a ->
-  Step s (Maybe e) a a
 switch' cur flag1 s1 flag2 s2 = Step $ \elapsed dt g e a ->
   case e of
     Nothing ->
@@ -141,11 +135,15 @@ switch' cur flag1 s1 flag2 s2 = Step $ \elapsed dt g e a ->
       let next
             | e' == flag1 = s1
             | e' == flag2 = s2
-            | otherwise = cur
+            | otherwise   = cur
           (a', s') = runStep next elapsed dt g e a
        in (a', switch' s' flag1 s1 flag2 s2)
 
--- | Construct a step that switches among multiple steps based on input.
+-- | Construct a step that switches among multiple steps based on input events.
+--
+-- The current step runs with every 'runStep' even when there are no new events.
+--
+-- The initial step is the identity, 'sid'.
 multiSwitch :: (Eq e, Ord e) => [(e, Step s (Maybe e) a a)] -> Step s (Maybe e) a a
 multiSwitch xs = multiSwitch' Nothing sid (Map.fromList xs)