(*) Exercise 2.2
Define a function regularPolygon :: Int -> Side -> Shape such that regularPolygon n s is a regular polygon with n sides, each of length s. (Hint: consider using some of Haskell's trigonometric functions, such as sin :: Float -> Float, cos :: Float -> Float, and tan :: Float -> Float.)
I'm a Haskell newbie, too, but I would use the angle between the line, which is defined from the point of orign to every corner of the polygon, and a coordinate axis. Then I would add some Postscript output for easier testing. http://www.frank-buss.de/tmp/polygons.png import System type Shape = [Vertex] type Side = Float type Vertex = (Float, Float) regularPolygon :: Int -> Side -> Shape regularPolygon n s = (buildList n) where buildList 0 = [] buildList i = let x = cos(alpha) * s y = sin(alpha) * s alpha = 2*pi/(fromIntegral n)*(fromIntegral i) in (x,y) : buildList (i-1) showVertex vertex = show (fst vertex) ++ " " ++ show (snd vertex) postscriptPolygon n s = (showVertex first ++ " moveto\n") ++ (unlines (map (\vertex -> (showVertex vertex ++ " lineto")) rest)) ++ (show (fst first) ++ " " ++ show (snd first) ++ " lineto") ++ "\n" where poly = regularPolygon n s first = head poly rest = tail poly main = do let file = "c:\\tmp\\test.ps" writeFile file ("20 20 scale 0.1 setlinewidth\n" ++ "5 5 translate\n" ++ (postscriptPolygon 4 4) ++ "8 4 translate\n" ++ (postscriptPolygon 7 2) ++ "stroke showpage\n") system ("c:\\Programme\\gs\\gs8.15\\bin\\gswin32.exe -g500x500 " ++ file) -- Frank Buss, fb@frank-buss.de http://www.frank-buss.de, http://www.it4-systems.de