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, toDeBruijn)
import Minilang.Lambda.Parser (desugar, parse, pretty)
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
  case parsed of
    Left err -> print err
    Right ast -> do
      putStrLn $ Text.unpack $ "Evaluating " <> pretty ast
      let termy = desugar ast
      putStrLn $ "Desugared to " <> show termy
      let term = toDeBruijn termy
      print $ eval term