Make error reports more comprehensible for the uninitiated

[oleks]

Currently it just prints a Haskell type.

[kirkedal]

This have now been improved

• 676793ea8432b80a30336e4f2385cc46c1801442

We would need a more detailed parsing to give more details

One points though, perhaps check should not report empty leaves as an invalid judgement. It is now just an indication of pending work.