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|
module Unlambda.Interpreter (
unlambda
) where
import System.IO.Error
import Control.Exception( Exception(..), Handler(..), throw, catches )
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 (eval Nothing term)
[ Handler ((\e -> return (endTerm e)) :: UnlambdaException -> IO UnlambdaTerm) ]
eval :: Maybe Char -> UnlambdaTerm -> IO UnlambdaTerm
eval ch term =
case term of
App f x -> do
t <- eval ch f
apply ch t x
_ -> return term
apply :: Maybe Char -> UnlambdaTerm -> UnlambdaTerm -> IO UnlambdaTerm
apply ch firstTerm secondTerm =
case firstTerm of
K -> eval ch secondTerm >>= return . Kpartial
Kpartial x -> eval ch secondTerm >> return x
S -> eval ch secondTerm >>= return . Spartial
Spartial x -> eval ch secondTerm >>= return . (Sapp x)
Sapp x y -> do
z <- eval ch secondTerm
result <- eval ch (App (App x z) (App y z))
return result
I -> eval ch secondTerm
V -> eval ch secondTerm >> return V
C -> return I --placeholder
D -> return (Promise secondTerm)
Promise x -> do
y <- eval ch secondTerm
result <- eval ch (App x y)
return result
Dot c -> putChar c >> eval ch secondTerm
R -> putChar '\n' >> eval ch secondTerm
E -> do
t <- eval ch secondTerm
throw (UnlambdaException t)
Reed -> do
t <- eval ch secondTerm
catchIOError (do
ch' <- getChar
eval (Just ch') (App t I)
) (\e -> eval Nothing (App t V))
Bar -> do
t <- eval ch secondTerm
case ch of
Just x -> eval ch (App t (Dot x))
Nothing -> eval ch (App t V)
Compare c -> do
t <- eval ch secondTerm
case (ch == Just c) of
True -> eval ch (App t I)
False -> eval ch (App t V)
|
