On Mon, Sep 13, 2010 at 09:53:21AM -0400, Brent Yorgey wrote:
On Mon, Sep 13, 2010 at 02:52:06PM +0200, Martin Tomko wrote:
Dear all, apologies for a newbie question, but I am returning to Haskell after years of hiatus and Java...
I have the following data type (representing geometries):
data Geometry = Point FID Coordinate | LineSegment FID (Coordinate,Coordinate) | Polyline FID [Coordinate] | Polygon FID [Coordinate] deriving (Show,Eq)
type Coordinate = (Float, Float)
And this is where I fail: I have no idea how to type getCoordinates, in order to match against the three different combinations -> it can result into a Coordinate, or a typle, or a List. I am sure it is possible!
Another thought: if it is important to be able to tell which sort of coordinates you have (single, pair, or list), you can make a new data type, like this: data CoordinateSet = Single Coordinate | Pair (Coordinate, Coordinate) | List [Coordinate] Now it should be no problem to write getCoordinates :: Geometry -> CoordinateSet -Brent