Re: Diagrammatic representation of Haskell datatypes

I was wondering if there exists diagrammatic languages for modelling Haskell datatypes?

The paper: "A visualisation of polymorphic type checking" Jung & Michaelson J. Functional Prog., 10(1), Jan 2000 describes a scheme for visualising Standard ML types and type-checking. The Vital system: http://www.cs.kent.ac.uk/projects/vital/ allows the values of Haskell datatypes to be graphically depicted and edited. Keith Hanna