Setting path on a shell script:

venvtest.hs

#!/usr/bin/env stack
-- stack --install-ghc runghc --package turtle

{-# LANGUAGE OverloadedStrings #-}

import Turtle
import System.Process(callProcess)

import qualified Data.Text as Text
-- adds virtualenv wrapper to path
addVirtualenvWrapper = do
  (exitSuccess, virtualenvwrapper) <- procStrict "which" ["virtualenvwrapper.sh"] empty
  shells virtualenvwrapper empty
  shells ("workon test") empty
  -- gives following error:
  --
  -- /bin/sh: workon: command not found
  -- venvtest.hs: ShellFailed {shellCommandLine = "workon test", shellExitCode = ExitFailure 127}

main = do
  addVirtualenvWrapper