65 lines
1.8 KiB
Haskell
65 lines
1.8 KiB
Haskell
module Interpreter (interFile) where
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import qualified Data.Map.Strict as Map
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import Lexer (lexL)
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import Parser (AstNode(..), parse)
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interFile :: FilePath -> IO ()
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interFile path = do
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putStrLn $ "Interpreting " ++ path
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content <- readFile path
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let ls = zip [1..] (lines content)
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mapM_ (uncurry interLine) ls
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interLine :: Int -> String -> IO ()
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interLine lineNum line =
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case lexL lineNum line of
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Left e -> error $ "Lexer error: " ++ e
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Right toks ->
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case parse toks of
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Left e -> error $ "Parser error: " ++ e
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Right ast ->
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case ast of
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Epsilon -> return ()
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_ -> do
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let result = evaluate ast
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putStrLn $ show ast ++ " => " ++ show result
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evaluate :: AstNode -> AstNode
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evaluate ast =
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let ast' = reduce ast Map.empty
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in if ast' == ast then ast else evaluate ast'
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reduce :: AstNode -> Map.Map String AstNode -> AstNode
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reduce (Abstraction p t) env =
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case p of
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Identifier pid ->
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let env' = Map.delete pid env
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in case t of
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Application tl tr
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| tr == p && not (isFree tl p) -> reduce tl env'
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_ -> Abstraction p (reduce t env')
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_ -> error "Invalid abstraction"
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reduce (Application l r) env =
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case l of
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Abstraction p body ->
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case p of
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Identifier pid ->
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let env' = Map.insert pid (reduce r env) env
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in reduce body env'
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_ -> error "Invalid application"
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_ -> Application (reduce l env) (reduce r env)
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reduce (Identifier id_) env =
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case Map.lookup id_ env of
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Just x -> x
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Nothing -> Identifier id_
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reduce Epsilon _ = Epsilon
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isFree :: AstNode -> AstNode -> Bool
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isFree (Abstraction p t) id_ = id_ /= p && isFree t id_
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isFree (Application l r) id_ = isFree l id_ || isFree r id_
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isFree (Identifier s) id_ = Identifier s == id_
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isFree _ _ = False
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