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Author | SHA1 | Date |
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Simon Bruder | f691bfccae | |
Simon Bruder | 4a767388fd | |
Simon Bruder | b9c0851beb | |
Simon Bruder | d823f5b33c | |
Simon Bruder | 5d956a3d89 | |
Simon Bruder | 002b834449 |
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/genstar/doc
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module Main where
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import Control.Monad (join)
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import Test.QuickCheck (Arbitrary (arbitrary))
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-- | One point of a path, consisting of its \(x\) and \(y\) coordinates.
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newtype Vertex = Point (Double, Double) deriving (Eq)
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instance Show Vertex where
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show (Point (x, y)) = show x ++ " " ++ show y
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instance Arbitrary Vertex where
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arbitrary = do
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x <- arbitrary
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y <- arbitrary
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return (Point (x, y))
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-- | 'vertexDistance' @p@
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-- returns the distance of a vertex to the origin
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vertexDistance :: Vertex -> Double
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vertexDistance (Point (x, y)) = sqrt (x ** 2 + y ** 2)
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-- | 'fromAngle' @angle@
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-- creates a point on the unit circle at the specified angle
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-- (specified in radians).
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fromAngle angle = Point (sin angle, cos angle)
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-- | 'scale' @s@ @p@ scales the vector to @p@ by the factor @s@.
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scale :: Double -> Vertex -> Vertex
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scale s (Point (x, y)) = Point (s * x, s * y)
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-- | 'move' @p1@ @p2@ adds the coordinates of @p1@ and @p2@,
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-- effectively moving @p1@ by @p2@ (or vice-versa).
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move :: Vertex -> Vertex -> Vertex
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move (Point (x1, y1)) (Point (x2, y2)) = Point (x1 + x2, y1 + y2)
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-- | Points \(p_0, p_2, \dots, p_{n-1}\)
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-- that should be connected,
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-- so that \(p_{i \bmod n}\) is connected to \(p_{i+1 \bmod n}\).
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newtype PolygonPath = PolygonPath [Vertex]
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instance Show PolygonPath where
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show (PolygonPath (v : vs)) = "<path d=\"M " ++ show v ++ join (map (\v -> " L " ++ show v) vs) ++ " Z\"/>\n"
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show (PolygonPath []) = ""
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-- | 'regularPolygonMod' @n@ @rf@ @pos@
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-- creates a regular @n@-gon
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-- with the center at @pos@
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-- that is modified in the sense that it takes @rf@,
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-- which is used to set the radius for each individual point.
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regularPolygonMod :: Integer -> (Integer -> Double) -> Vertex -> PolygonPath
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regularPolygonMod n rf pos = PolygonPath (map (\step -> move pos $ scale (rf step) $ fromAngle (fromInteger step * 2 * pi / fromInteger n)) [0 .. (n - 1)])
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-- | 'regularPolygon' @n@ @r@ @pos@
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-- creates a regular polygon
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-- with the radius @r@
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-- and the center at @pos@.
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regularPolygon :: Integer -> Integer -> Vertex -> PolygonPath
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regularPolygon n r = regularPolygonMod n (const (fromInteger r))
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-- | 'star' @n@ @r1@ @r2@ @pos@
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-- creates a star
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-- with @n@ spikes,
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-- the inner radius @r1@,
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-- the outer radius @r2@
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-- and the center @pos@.
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star :: Integer -> Double -> Double -> Vertex -> PolygonPath
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star n r1 r2 = regularPolygonMod (n * 2) ((take (fromInteger n * 2) (cycle [r1, r2]) !!) . fromInteger)
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main :: IO ()
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main = putStr $ join $ map (\n -> show n ++ "-gon: " ++ show (regularPolygon n 100 (Point (100, 100)))) [5, 8, 10, 15, 18, 30]
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{-# LANGUAGE TemplateHaskell #-}
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module Test where
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import Main (Vertex (Point), fromAngle, move, scale, vertexDistance)
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import Test.QuickCheck (discard, quickCheck, quickCheckAll)
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-- | the largest acceptable difference between two doubles so they are considered equal
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epsilon :: Double
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epsilon = 1e-10
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-- | checks whether the distance of a vertex constructed by 'fromAngle' to the origin is 1
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prop_VertexFromAngleDistance :: Double -> Bool
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prop_VertexFromAngleDistance angle = abs (1 - vertexDistance (fromAngle angle)) < epsilon
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-- | checks whether the distance of a vertex scaled by an factor is multiplied by that factor (absolute).
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prop_VertexScaleDistance :: (Vertex, Double) -> Bool
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prop_VertexScaleDistance (p, s) = abs (abs s * vertexDistance p - vertexDistance (scale s p)) < epsilon
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-- | checks whether moving a vertex by itself equals scaling it by 2
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prop_MoveSelfEqualsScale2 :: Vertex -> Bool
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prop_MoveSelfEqualsScale2 p = move p p == scale 2 p
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-- | checks whether moving a vertex by itself scaled by -1 equals the origin
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prop_MoveNegativeSelfEqualsOrigin :: Vertex -> Bool
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prop_MoveNegativeSelfEqualsOrigin p = move p (scale (-1) p) == Point (0, 0)
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return []
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check = $quickCheckAll
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main :: IO Bool
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main = check
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