Assert plugin

What

Drop in replacement for GHC's assert feature.

How to use:

• Use assert in your code.
• Turn on assertion checking by calling GHC with -fplugin=With.Assertions (otherwise assert doesn't have any effect the generated code)

Why

GHC's native assert only supports boolean assertions. So assert failures are not very informative. I wanted richer assertions, which could build up an assertion failure message (such as Validation in the validity package, which are supported out of the box by the assert plugin).