Parameterise things a little

Main.hs

@@ -8,11 +8,26 @@ import Graphics.Gloss.Geometry.Angle
 
 data PolarCoord = PolarCoord { radius :: Float, angle :: Float }
 
+majorMass :: Float
+majorMass = 10
+
+minorMass :: Float
+minorMass = 4
+
+framesPerSecond :: Int
+framesPerSecond = 120
+
+angularVelocity :: Float
+angularVelocity = pi
+
 render :: PolarCoord -> Picture
-render state = pictures [ circleSolid 10, translatePolar state $ circleSolid 10 ]
+render state = pictures [ circleSolid majorMass
+                        , translatePolar state $ circleSolid minorMass ]
 
 step :: a -> b -> PolarCoord -> PolarCoord
-step _ _ state = state { angle = normalizeAngle $ angle state + pi / 50 }
+step _ _ state = let radiansPerFrame = angularVelocity / fromIntegral framesPerSecond
+                     nextAngle = normalizeAngle $ angle state + radiansPerFrame
+                 in state { angle = nextAngle }
 
 translatePolar :: PolarCoord -> Picture -> Picture
 translatePolar q = rotate (radToDeg $ angle q) . translate (radius q) 0
@@ -21,4 +36,4 @@ window :: Display
 window = InWindow "Foo" (200, 200) (100, 100)
 
 main :: IO ()
-main = simulate window white 100 (PolarCoord 80 0) render step
+main = simulate window white framesPerSecond (PolarCoord 80 0) render step