How do I get a callstack in Haskell?

Question

I am trying to track down a non-exhaustive pattern in a libraries code. Specifically HDBC's mysql implementation. It is trying to match over types in my program and map them to mysql's types I believe. I can't seem to get a callstack for this error which means that since there are a number of parameters to the SQL query it is difficult to track down exactly what is causing it.

Is it possible to get a callstack in haskell so I would know which parameter was causing the error? Also I would think that this should be caught by the compiler since it should be able to look at my types and the patterns and make sure that there was a corresponding match.

Answer 1

You can use the GHCi debugger to identify where the exception is coming from.

I walk through a full example here.

Answer 2

You might also take a look at the Debug.Trace library.