check_lean_version

#!/usr/bin/env stack
-- stack --resolver lts-9.13 --install-ghc runghc --package MissingH

import Control.Monad
import Data.Char
import Data.String.Utils
import System.Exit
import System.Process

main = do
  xs <- readProcess "lean" ["-v"] ""
  let hash = takeWhile isAlphaNum $ dropWhile (/= "commit") (words xs) !! 1
  expected <- strip <$> readFile "lean_version"
  let expected' = take 12 expected
  unless (expected' == hash) $ do
    putStrLn "Wrong version of Lean found, expecting:"
    putStrLn $ "> " ++ expected
    exitFailure