(+) at least it's drawing

src/Canvas.hs

@@ -1,6 +1,6 @@
 module Canvas where
 
-import Graphics.Gloss.Data.Picture ( Picture (Text), pictures, scale, translate )
+import Graphics.Gloss.Data.Picture ( Picture (Text, Blank), pictures, scale, translate, rectangleSolid, circle )
 import Graphics.Gloss.Interface.IO.Interact ( Event (EventKey, EventMotion), KeyState (Down, Up), Key (Char, MouseButton), MouseButton (LeftButton) )
 
 type Dimension  = (Int, Int)
@@ -17,10 +17,18 @@ data Canvas = Canvas {
 
 data Mode = Brush | Eraser deriving (Eq, Show)
 
-newtype Tip = Shape TipSize 
+data Tip = Tip {
+    shape   :: Shape
+,   size    :: TipSize
+}
 
 data Shape = Rectangular | Circular
 
+nextPicture :: Canvas -> Picture
+nextPicture (Canvas _ Brush True position (Tip Rectangular size)) = uncurry translate position $ rectangleSolid size size
+nextPicture (Canvas _ Brush True position (Tip Circular size)) = uncurry translate position $ circle size
+nextPicture _ = Blank
+
 windowSize :: Dimension
 windowSize = (500, 500)
 
@@ -49,5 +57,5 @@ handle (EventMotion (x, y)) canv                          = canv { pos = (x, y)}
 handle _ canv = canv
 
 update :: Float -> Canvas -> Canvas
-update _ canv = canv
+update _ canv = canv { items = nextPicture canv : items canv }
 

src/Costants.hs

@@ -16,5 +16,5 @@ initial = Canvas {
 ,   mode    =   Brush
 ,   drawing =   False
 ,   pos     =   (0, 0)
-,   tip     = Rectangular 3
+,   tip     =   Tip Rectangular 3
 }