Hello, I'm getting really frustrated by error handling in haskell. By this I mean "assert"-like errors. Which means, something that should never happen, happens. This will happen in the development and deployment of software of any size. When coding the feature you'll say, I don't need to handle the "Nothing" case, because it will never happen, or almost never, and this is not critical production software. But if one day it happens you find yourself with a several thousand lines program and all you have to debug is the input data (most of the time anyway, sometimes not even that) and this error message (for instance): *** Exception: Prelude.head: empty list And you don't know even, did you call "head" or maybe a library you are using called it. This is really poor compared to what Java, python and others offers. I can understand that it's difficult to provide a stack trace, especially with lazy evaluation, but at least the function name and maybe a line number... Actually I don't know why it would be so difficult to also give me the values of the parameters of the function... using print and if it's a pure function it intuitively doesn't seem difficult. I've tried ghci with :trace and ":set -fbreak-on-exception" and I got nowhere. It breaks in things which are not important (I have no idea where it breaks, it claims an exception was thrown, maybe but not in my code and it never reaches my code for sure). After hitting ":continue" many times, I get to my exception and there I didn't manage to get useful information (:hist never printed me anything). But I would like not to have to use ghci at all. And to avoid having to write all over the place in my code these "else" and case situations for things I assume are impossible (these are cases I would not write in other modern languages). This is a feature for which I would be ready to pay a 50% speed penalty and 50% memory use penalty. I understand if it's the haskell way of writing all those else clauses... But I think in that case it really makes it compare negatively to other languages. It would be a real minus in my opinion (including to code readability). I have read (quickly) those but didn't find the solution there: http://www.haskell.org/ghc/docs/7.0.1/html/users_guide/ghci-debugger.html http://book.realworldhaskell.org/read/error-handling.html Any advice will be welcome! I really hope I missed something. Emmanuel