Hello! I have a class Drawable, and some datatypes which are instances of it, and I would like to be able to draw them all at once! drawMany window [image, text, otherImage] I think the type of the function drawMany would be: drawMany :: Window -> [forall a. (Drawable a) => a] -> IO () However it doesn't work. I know one solution is to make a new datatype (e.g. DrawableObj) which will be: data DrawableObj = forall a (Drawable a) => DrawableObj a And then declare drawMany as: drawMany :: Window -> [DrawableObj] -> IO () But to use it I have to wrap up myself every drawable in a DrawableObj: drawMany window [DrawableObj image, DrawableObj text, DrawableObj otherImage] Is there another more suitable way to handle a list of drawables? ----- Yves Parès Live long and prosper -- View this message in context: http://old.nabble.com/Lists-of-Existential-DT-tp27735354p27735354.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.