Hello, I am trying to model multigraphs ....but getting errors with ghci and can't figure out why.... I have a serious blind spot .... {-# LANGUAGE MultiParamTypeClasses, FunctionalDependencies #-} module Bonzo where class Graph arrow node where source :: arrow -> node target :: arrow -> node data Arrow = Arrow (Int, Int) instance Graph Arrow Int where source Arrow = fst Arrow target Arrow = snd Arrow ~ ~ {-# LANGUAGE MultiParamTypeClasses, FunctionalDependencies #-} module Bonzo where class Graph arrow node where source :: arrow -> node target :: arrow -> node data Arrow = Arrow (Int, Int) instance Graph Arrow Int where source Arrow = fst Arrow target Arrow = snd Arrow ~ ~ ghci> :load junk1.hs [1 of 1] Compiling Bonzo ( junk1.hs, interpreted ) junk1.hs:19:12: Constructor `Arrow' should have 1 argument, but has been given 0 In the pattern: Arrow In the definition of `source': source Arrow = fst Arrow In the instance declaration for `Graph Arrow Int' junk1.hs:21:12: Constructor `Arrow' should have 1 argument, but has been given 0 In the pattern: Arrow In the definition of `target': target Arrow = snd Arrow In the instance declaration for `Graph Arrow Int' Regards, Vasili