A monad transformer for tracing provenience of errors

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MIT licensed by Jon Sterling
Maintained by


A monad transformer for tracing error provenience. If you want a nice example of how to use it, this bidirectional type checker provides a very nice example and motivation.


  • Provided MonadTrace instances to the transformers menagerie.

  • Provided the various mtl instance to TraceT.

  • Based TraceT on ExceptT to shed the either package dependency.

  • Remove some things that were of limited utility which had caused profunctors, kan-extensions dependencies to be incurred.

  • Added a Monad superclass constraint to MonadTrace.

  • Added Typeable, Generic, and NFData instances for ErrorTrace.
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