haskell/step1_read_print.hs

   1 import System.IO (hFlush, stdout)
   2 import Control.Monad.Except (runExceptT)
   3 import Control.Monad.Trans (liftIO)
   4
   5 import Readline (addHistory, readline, load_history)
   6 import Types
   7 import Reader (read_str)
   8 import Printer (_pr_str)
   9
  10 -- read
  11
  12 mal_read :: String -> IOThrows MalVal
  13 mal_read = read_str
  14
  15 -- eval
  16
  17 eval :: MalVal -> MalVal
  18 eval = id
  19
  20 -- print
  21
  22 mal_print :: MalVal -> IOThrows String
  23 mal_print = liftIO. Printer._pr_str True
  24
  25 -- repl
  26
  27 rep :: String -> IOThrows String
  28 rep line = mal_print =<< (eval <$> mal_read line)
  29
  30 repl_loop :: IO ()
  31 repl_loop = do
  32     line <- readline "user> "
  33     case line of
  34         Nothing -> return ()
  35         Just "" -> repl_loop
  36         Just str -> do
  37             addHistory str
  38             res <- runExceptT $ rep str
  39             out <- case res of
  40                 Left mv -> (++) "Error: " <$> liftIO (Printer._pr_str True mv)
  41                 Right val -> return val
  42             putStrLn out
  43             hFlush stdout
  44             repl_loop
  45
  46 main :: IO ()
  47 main = do
  48     load_history
  49
  50     repl_loop