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.Eval (eval)
import System.IO (Handle)
import Minilang.Lambda.Parser (parse, desugar)

-- | 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
      result = case parsed of
         Left err -> show err
         Right ast ->
           let term = desugar ast
               env = mempty
           in show $ eval term env

  BS.hPut
    hout
    (encodeUtf8 (Text.pack result <> "\n"))