Hi, Trying to get up to speed in Haskell, I'm playing with doing some abstraction in data types. Specifically, I have this: type Cartesian_coord = Float type Latitude = Float type Longitude = Float data Point = Cartesian (Cartesian_coord, Cartesian_coord) | Spherical (Latitude, Longitude) type Center = Point type Radius = Float data Shape = Circle Center Radius | Polygon [Point] This obviously stinks since a Polygon could contain mixed Cartesian and Spherical points. Polygon needs to be one or the other, but not mixed. I could define seperate types for Cartesian and Spherical and seperate CartesianPoly and SphericalPoly, but that doesn't seem very elegant and also increases as I add more coordinate systems and shapes. I read a little on GADTs, et al, but I'm not sure if that's what I want for this or not. Any help appreciated! -- Darrin Chandler | Phoenix BSD User Group | MetaBUG dwchandler@stilyagin.com | http://phxbug.org/ | http://metabug.org/ http://www.stilyagin.com/ | Daemons in the Desert | Global BUG Federation