Sample Haskell project using embedded Ruby as a preprocessor

A.hs

module A where

B.erb

module B where

<% (1..5).each do |i| %>
test<%= i %> :: Int
test<%= i %> = <%= i %>
<% end %>

ghctest.cabal

name:                 ghctest
version:              0.1
build-type:           Custom
cabal-version:        >= 1.10

library
  exposed-modules:      A, B
  build-depends:        base
  default-language:     Haskell2010

custom-setup
  setup-depends:        base, Cabal, process

Setup.hs

module Main where

import Distribution.Simple
import Distribution.Simple.PreProcess
import System.Process (readProcess)

runRuby _ _ = PreProcessor
  { platformIndependent = True
  , runPreProcessor = mkSimplePreProcessor $ \erbFile fout verbosity -> do
    readProcess "erb" [erbFile] "" >>= writeFile fout
  }

main :: IO ()
main = defaultMainWithHooks simpleUserHooks
  { hookedPreProcessors = [("erb", runRuby)]
  }