Re: [Haskell-cafe] Area from [(x,y)] using foldl

Sorry, I forgot to add that if the polygon is very far from the origin, you may have overflow or increased round off error; it is better to translate the polygon back to the origin, before doing the area calculation. How about these BETTER type signatures. -- Area of a Polygon import Data.List type X = Double type Y = Double type Area = Double poly1 = [(0,1),(5,0),(3,4)]::[(X,Y)] areaPoly :: [(X,Y)] -> Area areaPolyCalc :: (Area,(X,Y)) -> (X,Y) -> (Area,(X,Y)) areaPoly (pt:pts) = 0.5 * (fst (foldl' areaPolyCalc (0,pt) pts)) areaPolyCalc (sum,(x,y)) (xNext,yNext) = (sum + (x * yNext - xNext * y),(xNext,yNext)) -- Regards, Casey