The builtin breakpoint functionality in GHCi is in a partially broken state, particularly with regards to concurrent programs such as web servers, and is not being actively maintained. As an attempt to remedy this situation, I have developed a GHC plugin that provides breakpoint functionality that works in concurrent contexts and is furthermore not dependent on the bytecode interpreter. I believe that this work could have significant value for industrial users and that the implementation details would be of interest to GHC hackers. See the Github repo for more info.