Previous Version is a simple Haskell tool that allows retrieving several versions of the same module from git. The preprocessor will analyse the imports from your Haskell files and extract the corresponding versions.

Add the following line in the header of your Haskell file:

{-# OPTIONS_GHC -F -pgmF prevproc #-}

You can now include previous versions of your imports:

import TypesV0
import TypesV1

The preprocessor will automatically extract the versions tagged V0 and V1 of the file Types.hs from your git repository. The extracted files will be placed in dist/build/autogen and renamed to match the imports.

Previous Version is used for "continuous data integration". See the example folder for an exemple repository doing continuous data integration using previous-version.