Example on how to use Compact values for serialisation with GHC

CompactTest.hs

#!/usr/bin/env stack
-- stack --resolver lts-11.22 script --optimize

{-# OPTIONS_GHC -Wall #-}
{-# LANGUAGE ScopedTypeVariables #-}

import           Data.Compact (compact, getCompact)
import           Data.Compact.Serialize (writeCompact, unsafeReadCompact)
import           System.Environment (getArgs)

-- Note: You cannot compact pinned values, like `ByteString`s.
-- That fails with: compaction failed: cannot compact mutable objects

type Val = [Int]

main :: IO ()
main = do
  args <- getArgs
  let path = "/tmp/compactfile"
  case args of
    ["write"] -> do
      let val :: Val
          val = [1..1000000]
      c <- compact val
      writeCompact path c
    ["read"] -> do
      eCompact <- unsafeReadCompact path
      case eCompact of
        Left err -> fail $ "Could not deserialise " ++ path ++ ": " ++ err
        Right c -> do
          let val :: Val
              val = getCompact c
          print (sum val)
    _ -> error "bad arguments"