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module Unlambda.Interpreter (
unlambda
) where
import System.IO.Error
import Control.Exception( Exception(..), Handler(..), throw, catches )
import Control.Monad.Trans.Class
import Control.Monad.Trans.Cont
import Control.Monad.Trans.State.Lazy
import Control.Monad.IO.Class
import Data.Typeable
import Data.Maybe
import Unlambda.Parser
type ULM a = ContT UnlambdaTerm (StateT (Maybe Char) IO) a
data UnlambdaException = UnlambdaException { exitValue :: UnlambdaTerm }
deriving (Show, Typeable)
instance Exception UnlambdaException
unlambda :: UnlambdaTerm -> IO UnlambdaTerm
unlambda term = catches ((`evalStateT` Nothing) . (`runContT` return) $ eval term)
[ Handler ((\e -> return . exitValue $ e) :: UnlambdaException -> IO UnlambdaTerm) ]
setCurChar :: Maybe Char -> ULM ()
setCurChar x = lift (put x)
getCurChar :: ULM (Maybe Char)
getCurChar = lift (get)
eval :: UnlambdaTerm -> ULM UnlambdaTerm
eval term =
case term of
App f x -> do
t <- eval f
apply t x
_ -> return term
apply :: UnlambdaTerm -> UnlambdaTerm -> ULM UnlambdaTerm
apply firstTerm secondTerm =
case firstTerm of
K -> eval secondTerm >>= return . Kpartial
Kpartial x -> eval secondTerm >> return x
S -> eval secondTerm >>= return . Spartial
Spartial x -> eval secondTerm >>= return . (Sapp x)
Sapp x y -> do
z <- eval secondTerm
eval (App (App x z) (App y z))
I -> eval secondTerm
V -> eval secondTerm >> return V
C -> callCC $ \cont -> eval (App secondTerm (Continuation cont))
Continuation cont -> eval secondTerm >>= cont
D -> return (Promise secondTerm)
Promise x -> eval secondTerm >>= eval . (App x)
Dot c -> do
t <- eval secondTerm
liftIO (putChar c)
return t
R -> do
t <- eval secondTerm
liftIO (putChar '\n')
return t
E -> eval secondTerm >>= throw . UnlambdaException
Reed -> do
t <- eval secondTerm
ch <- liftIO (catchIOError (getChar >>= return . Just) (\e -> return Nothing))
setCurChar ch
if (isNothing ch) then eval (App t V) else eval (App t I)
Bar -> do
t <- eval secondTerm
ch <- getCurChar
if (isNothing ch) then eval (App t V) else eval (App t I)
Compare c -> do
t <- eval secondTerm
ch <- getCurChar
if (ch /= Just c) then eval (App t V) else eval (App t I)
|
