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What are some open source programs that use Haskell and can be considered to be good quality modern Haskell? The larger the code base, the better.

I want to learn from their source code. I feel I'm past the point of learning from small code examples, which are often to esoteric and small-world. I want to see how code is structured, how monads interact when you have a lot of things going on (logging, I/O, configuration, etc.).