<html><head><style type="text/css"><!-- DIV {margin:0px;} --></style></head><body><div style="font-family:arial,helvetica,sans-serif;font-size:12pt">Hi,<br><br>I've defined the datatype:<br><br>data Graph a b = Empty | Context a b :& Graph a b<br><br> and the function<br><br> isEmpty :: Graph a b -> Bool<br> isEmpty Empty = True<br> isEmpty _ = False<br><br>and when I do a test run with the graph, <br>( [ ],2,'c',[("down",3)]) :& Empty<br><br>Haskell is bringing the message " Not in scope: data constructor `:&' "<br>Why is that so?<br><div> </div><br><div> </div><span style="font-weight: bold; color: rgb(0, 64, 127);"><span style="font-style: italic;">Kind regards</span></span></div><br>
</body></html>