[Haskell-cafe] Debug tracing in Haskell

[MarLinn]

This sounds an awful lot like a different name for what monad-logger offers.

Pro:
+ uses Template Haskell for decoupling and to add source positions
+ used in Yesod so probably well maintained
+ the underlying fast-logger was optimized for performance, including in 
concurrent production environments

Contra:
- only usable in monadic contexts
- I haven't found a better documentation than looking at how its used in 
Yesod source code

Pro/Contra:
* The package is from the Yesod/Stack corner of our world, so depending 
on your political viewpoint this can be anything from a bonus to a 
deal-breaker ;-)