Each module which enables the TemplateHaskell language pragma gets recompiled more often than necessary when dependencies change. It would be nice to bypass that by removing the usage of TemplateHaskell. A number of modules in the codebase are only using TemplateHaskell to safely create Path values, e.g. mkRelFile or mkRelDir. I recommend collecting these usages into a single module, likely Stack.Constants, and importing for there. That would allow us to reduce recompilation time and improve the project iteration cycle a bit.

I'm open to this being shot down, since I'm not at all the expert on fast iteration cycles :). CC @chrisdone and @bitemyapp.