* David Thomas
Is there a library that provides a near-complete solution for this? I looked around a bit and found many (many!) partial solutions on hackage, but nothing that really does it all. In coding it up for my own projects, however, I can't help but feel like I must be reinventing the wheel.
What I want is something that will process command line options (this seems to be where most packages are targetted), environment variables, and settings files (possibly specified in options), and override/default appropriately.
Did I miss something?
If not, I'd like to see about fixing the situation, but very much want to avoid the whole "There were X libraries that didn't quite do it right; now there's X+1!" thing. Are there any opinions as to which of the many libraries is likely the best starting point if I'm going to contribute to one of them?
What functionality would such a library provide? There is a variety of good command-line parsing libraries and even more possible configuration file formats. I don't think you want to commit to some particular command-line syntax or config file format for the library to be generally useful (and I don't see any benefit of doing so). But then the only part that remains is just combining the settings, which is a simple monoidal operation. Just define the data type of your settings, define/derive a Monoid instance for it in spirit of First/Last monoids, and then mappend them in the right order. (I also mostly concur with what Ben wrote on this subject.) Roman