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module Eval
( evalMain
) where
import Control.Exception
import Control.Monad.State
import Debug.Trace
import Parser
import System.Console.Haskeline
import System.Environment
import System.Exit
import System.IO
import Text.Parsec hiding ( State
, try
)
type Environment = [(String, Expression)]
type Program = State Environment
eval :: [String] -> Environment -> IO Environment
eval [] env = pure env
eval (line : ls) env = case parse parseLine "Evaluator" line of
Left err -> print err >> pure env
Right instr -> case instr of
Define name exp ->
let (res, env') = evalDefine name exp `runState` env
in case res of
Left err -> print err >> eval ls env'
Right _ -> eval ls env'
Evaluate exp -> putStrLn "ok" >> pure env
_ -> eval ls env
evalVar :: String -> Program (Failable Expression)
evalVar var = state $ \e ->
( case lookup var e of
Nothing -> Left $ UndeclaredFunction var
Just x -> Right x
, e
)
evalApp :: Expression -> Expression -> Program (Failable Expression)
evalApp f g =
evalExp f
>>= (\case
Left e -> pure $ Left e
Right f' -> fmap (Application f') <$> evalExp g
)
evalExp :: Expression -> Program (Failable Expression)
evalExp idx@(Bruijn _ ) = pure $ Right idx
evalExp ( Variable var) = evalVar var
evalExp ( Abstraction exp) = evalExp exp
evalExp ( Application f g) = evalApp f g
evalDefine :: String -> Expression -> Program (Failable Expression)
evalDefine name exp =
evalExp exp
>>= (\case
Left e -> pure $ Left e
Right f -> modify ((name, f) :) >> pure (Right f)
)
evalFile :: String -> IO ()
evalFile path = do
file <- try $ readFile path :: IO (Either IOError String)
case file of
Left exception -> print (exception :: IOError)
Right file -> eval (lines file) [] >> putStrLn "Done"
evalRepl :: String -> Environment -> InputT IO Environment
evalRepl line env = outputStrLn (show env) >> pure env
repl :: Environment -> InputT IO ()
repl env =
getInputLine ":: "
>>= (\case
Nothing -> pure ()
Just line -> evalRepl line env >>= repl
)
usage :: IO ()
usage = putStrLn "Invalid arguments. Use 'bruijn [file]' instead"
evalMain :: IO ()
evalMain = do
args <- getArgs
case args of
[] -> runInputT defaultSettings { historyFile = Just ".brown-history" }
$ repl []
[path] -> evalFile path
_ -> usage
|
