Add tab bar functions (#30)

Main.hs

@@ -5,6 +5,7 @@
 
 module Main (main) where
 
+import Control.Monad
 import Data.IORef
 import DearImGui
 import DearImGui.OpenGL
@@ -33,7 +34,9 @@ main = do
       pos <- newIORef $ ImVec2 64 64
       size' <- newIORef $ ImVec2 512 512
       selected <- newIORef 4
-      loop w checked color slider r pos size' selected
+      tab1 <- newIORef True
+      tab2 <- newIORef True
+      loop w checked color slider r pos size' selected tab1 tab2
 
       openGL2Shutdown
 
@@ -47,8 +50,10 @@ loop
   -> IORef ImVec2 
   -> IORef ImVec2
   -> IORef Int 
+  -> IORef Bool
+  -> IORef Bool
   -> IO ()
-loop w checked color slider r pos size' selected = do
+loop w checked color slider r pos size' selected tab1Ref tab2Ref = do
   quit <- pollEvents
 
   openGL2NewFrame
@@ -70,8 +75,22 @@ loop w checked color slider r pos size' selected = do
   setNextWindowBgAlpha 0.42
 
   begin "My Window"
+
   text "Hello!"
 
+  beginTabBar "My tab bar" ImGuiTabBarFlags_Reorderable >>= whenTrue do
+    beginTabItem "Tab 1" tab1Ref ImGuiTabBarFlags_None >>= whenTrue do
+      text "Tab 1 is currently selected."
+      endTabItem
+    beginTabItem "Tab 2" tab2Ref ImGuiTabBarFlags_None >>= whenTrue do
+      text "Tab 2 is selected now."
+      endTabItem
+    reOpen <- tabItemButton "ReopenTabs" ImGuiTabItemFlags_Trailing
+    when reOpen do
+      writeIORef tab1Ref True
+      writeIORef tab2Ref True
+    endTabBar
+
   listBox "Items" r [ "A", "B", "C" ]
 
   button "Click me" >>= \case
@@ -147,7 +166,7 @@ loop w checked color slider r pos size' selected = do
 
   glSwapWindow w
 
-  if quit then return () else loop w checked color slider r pos size' selected
+  if quit then return () else loop w checked color slider r pos size' selected tab1Ref tab2Ref
 
   where