[curryhoward]

The suggestion is to use pure Haskell for the rules DSL only. The surrounding system that applies any side effects would presumably not be written in that language.

It's a good idea, and Facebook actually does something like this for their spam filtering rules: https://engineering.fb.com/2015/06/26/security/fighting-spam...

[daxfohl]

Looks like it has become abandonware, or at least the component they open sourced. Oh well, such is life in the Haskell ecosystem. https://github.com/facebook/Haxl