module Minilang.IO where

import qualified Data.ByteString as BS
import qualified Data.Text as Text
import Data.Text.Encoding
  ( decodeUtf8With,
    encodeUtf8,
  )
import Data.Text.Encoding.Error (lenientDecode)
import Minilang.Lambda.DeBruijn (eval, fromDeBruijn, toDeBruijn)
import Minilang.Lambda.Parser (desugar, parse, pretty, resugar)
import System.IO (Handle)

-- | Read a "program" from @hin@ handle, evaluate it and dump the result
-- on @hout@.
runEval :: Handle -> Handle -> IO ()
runEval hin hout = do
  programText <- decodeUtf8With lenientDecode <$> BS.hGetContents hin
  let parsed = parse programText
  let result =
        case parsed of
          Left err -> Text.pack $ show err
          Right ast ->
            let evaluate =
                  pretty
                    . resugar
                    . fromDeBruijn
                    . eval
                    . toDeBruijn
                    . desugar
             in evaluate ast

  BS.hPut
    hout
    (encodeUtf8 result)