Compile or load it into a Haskell interpreter and evaluate main. The current textual user interface is rather simple. You first have to choose an example program and then choose between free navigation and algorithmic debugging. Both have many variants, the command ? gives an overview of the available commands. All examples are hard-coded in abstract syntax at the end of the source code. It should not be too difficult to add further examples. If you have interesting examples, please send them to me, just like any comments you have.
TypeIlluminator currently handles class contexts, but it does not yet help understanding them.
Note that the source contains code of Mark Jones' Typing Haskell in Haskell.
Removed several bugs. Improved pretty printing. Written in Haskell 2010 for ghci.
Version demonstrated at ICFP'01, as described in the paper Compositional Explanation of Types and Algorithmic Debugging of Type Errors. Written in Haskell 98 for Hugs98.