don't scroll past top of page

src/Mtlstats/Actions.hs

@@ -38,6 +38,8 @@ module Mtlstats.Actions
   , resetGoalData
   , assignPMins
   , backHome
+  , scrollUp
+  , scrollDown
   ) where
 
 import Control.Monad.Trans.State (modify)
@@ -237,3 +239,11 @@ backHome
   = (progMode     .~ MainMenu)
   . (inputBuffer  .~ "")
   . (scrollOffset .~ 0)
+
+-- | Scrolls the display up
+scrollUp :: ProgState -> ProgState
+scrollUp = scrollOffset %~ max 0 . pred
+
+-- | Scrolls the display down
+scrollDown :: ProgState -> ProgState
+scrollDown = scrollOffset %~ succ

src/Mtlstats/Control.hs

@@ -278,8 +278,8 @@ reportC = Controller
     return C.CursorInvisible
   , handleController = \e -> do
     case e of
-      C.EventSpecialKey C.KeyUpArrow   -> modify $ scrollOffset %~ pred
-      C.EventSpecialKey C.KeyDownArrow -> modify $ scrollOffset %~ succ
+      C.EventSpecialKey C.KeyUpArrow   -> modify scrollUp
+      C.EventSpecialKey C.KeyDownArrow -> modify scrollDown
       C.EventSpecialKey C.KeyHome      -> modify $ scrollOffset .~ 0
       C.EventSpecialKey _              -> modify backHome
       C.EventCharacter _               -> modify backHome