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module Unlambda.Interpreter (
unlambda
) where
import System.IO.Error
import Control.Exception( Exception(..), Handler(..), throw, catches )
import Control.Monad.Trans.Cont
import Control.Monad.IO.Class
import Data.Typeable
import Unlambda.Parser
data UnlambdaException = UnlambdaException { endTerm :: UnlambdaTerm }
deriving (Show, Typeable)
instance Control.Exception.Exception UnlambdaException
unlambda :: UnlambdaTerm -> IO UnlambdaTerm
unlambda term =
catches ((`runContT` return) $ eval term)
[ Handler ((\e -> return (endTerm e)) :: UnlambdaException -> IO UnlambdaTerm) ]
eval :: UnlambdaTerm -> ContT UnlambdaTerm IO UnlambdaTerm
eval term =
case term of
App f x -> do
t <- eval f
apply t x
_ -> return term
apply :: UnlambdaTerm -> UnlambdaTerm -> ContT UnlambdaTerm IO 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
result <- eval (App (App x z) (App y z))
return result
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 -> do
y <- eval secondTerm
result <- eval (App x y)
return result
Dot c -> do
t <- eval secondTerm
liftIO (putChar c)
return t
R -> do
t <- eval secondTerm
liftIO (putChar '\n')
return t
E -> do
t <- eval secondTerm
throw (UnlambdaException t)
Reed -> return I --do
--t <- eval ch secondTerm
--catchIOError (do
-- ch' <- getChar
-- eval (Just ch') (App t I)
-- ) (\e -> eval Nothing (App t V))
Bar -> return I --do
--t <- eval ch secondTerm
--case ch of
-- Just x -> eval ch (App t (Dot x))
-- Nothing -> eval ch (App t V)
Compare c -> return I --do
--t <- eval ch secondTerm
--case (ch == Just c) of
-- True -> eval ch (App t I)
-- False -> eval ch (App t V)
|
