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Interpreter.hs
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Interpreter.hs
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{-# LANGUAGE LambdaCase #-}
module Interpreter where
import Control.Monad.Except
import Control.Monad.Reader
import Control.Monad.State
import Data.Map.Lazy (Map, empty, insert, (!?))
import Ruskell.Abs
import Ruskell.ErrM
data List = IntListV [Integer] | BoolListV [Bool] | EmptyList
deriving (Eq)
instance Show List where
show (IntListV il) = show il
show (BoolListV bl) = show bl
show EmptyList = "[]"
data Lambda = ExpF Exp | LambdaF Ident Lambda
deriving (Eq)
instance Show Lambda where
show (ExpF e) = show e
show (LambdaF (Ident x) e) = "<function>"
data Value = BoolV Bool | IntV Integer | ListV List | FunV Lambda Env
deriving (Eq)
instance Show Value where
show (IntV n) = show n
show (ListV il) = show il
show (BoolV b) = show b
show (FunV f e) = show f
type Env = Map String Value
-- nicer-looking error messages
prettyBNFC :: BNFC'Position -> String
prettyBNFC p = case p of
Just (l, c) -> "line " ++ show l ++ ", column " ++ show c
Nothing -> "?"
interpreterError :: BNFC'Position -> String -> ReaderT Env Err Value
interpreterError p m = throwError ("error at " ++ prettyBNFC p ++ ":\n" ++ m)
-- helper functions
allInts :: [Value] -> Bool
allInts =
all
( \case
IntV _ -> True
_ -> False
)
allBools :: [Value] -> Bool
allBools =
all
( \case
BoolV _ -> True
_ -> False
)
eval :: Exp -> ReaderT Env Err Value
-- literals and simple expressions
eval (LitE _ n) = case n of
IntL _ n -> return $ IntV n
TL _ -> return $ BoolV True
FL _ -> return $ BoolV False
eval (NotE p e) = do
e' <- eval e
case e' of
BoolV e'' -> return $ BoolV $ not e''
_ -> interpreterError p ("Invalid usage of 'not' on " ++ show e')
eval (NegE p e) = do
e' <- eval e
case e' of
IntV e'' -> return $ IntV $ -e''
_ -> interpreterError p ("Invalid usage of '-' on " ++ show e' ++ ".")
eval (OrE p l r) = do
l' <- eval l
r' <- eval r
case (l', r') of
(BoolV l'', BoolV r'') -> return $ BoolV $ l'' || r''
_ -> interpreterError p ("Cannot use '||' between " ++ show l' ++ " and " ++ show r' ++ ".")
eval (AndE p l r) = do
l' <- eval l
r' <- eval r
case (l', r') of
(BoolV l'', BoolV r'') -> return $ BoolV $ l'' && r''
_ -> interpreterError p ("Cannot use '&&' between " ++ show l' ++ " and " ++ show r' ++ ".")
eval (AddE p l o r) = do
l' <- eval l
r' <- eval r
case (l', r') of
(IntV l'', IntV r'') ->
case o of
AddO _ -> return $ IntV $ l'' + r''
SubO _ -> return $ IntV $ l'' - r''
_ -> interpreterError p "Invalid usage of '+' or '-' between not-integers."
eval (MulE p l o r) = do
l' <- eval l
r' <- eval r
case (l', r') of
(IntV l'', IntV r'') ->
case o of
MulO _ -> return $ IntV $ l'' * r''
DivO p' -> case r'' of
0 -> interpreterError p' "Division by zero."
_ -> return $ IntV $ l'' `div` r''
_ -> interpreterError p "Invalid usage of '*' or '/' between not-integers."
eval (RelE p l o r) = do
l' <- eval l
r' <- eval r
case (l', r') of
(IntV l'', IntV r'') ->
case o of
LtO _ -> return $ BoolV $ l'' < r''
LeO _ -> return $ BoolV $ l'' <= r''
GtO _ -> return $ BoolV $ l'' > r''
GeO _ -> return $ BoolV $ l'' >= r''
EqO _ -> return $ BoolV $ l'' == r''
NeO _ -> return $ BoolV $ l'' /= r''
(BoolV l'', BoolV r'') ->
case o of
EqO _ -> return $ BoolV $ l'' == r''
NeO _ -> return $ BoolV $ l'' /= r''
_ -> interpreterError p "Invalid comparison between bools."
(ListV l'', ListV r'') ->
case (l'', r'') of
(IntListV l''', IntListV r''') ->
case o of
EqO _ -> return $ BoolV $ l''' == r'''
NeO _ -> return $ BoolV $ l''' /= r'''
_ -> interpreterError p "Invalid comparison between lists."
(BoolListV l''', BoolListV r''') ->
case o of
EqO _ -> return $ BoolV $ l''' == r'''
NeO _ -> return $ BoolV $ l''' /= r'''
_ -> interpreterError p "Invalid comparison between lists."
(EmptyList, EmptyList) ->
case o of
EqO _ -> return $ BoolV True
NeO _ -> return $ BoolV False
_ -> interpreterError p "Invalid comparison between lists."
_ -> interpreterError p "Invalid comparison between lists of different types."
(FunV l'' _, FunV r'' _) ->
interpreterError p "Cannot compare functions."
_ -> interpreterError p "Invalid comparison between different types."
-- variables
eval (VarE p (Ident var)) = do
env <- ask
case env !? var of
Just val -> case val of
FunV fun env' -> case fun of
ExpF exp -> local (const $ insert var val env') (eval exp)
LambdaF _ _ -> return $ FunV fun (insert var val env')
_ -> return val
Nothing -> interpreterError p ("Variable " ++ var ++ " not found.")
-- if
eval (IfE p c t f) = do
c' <- eval c
case c' of
BoolV c'' -> if c'' then eval t else eval f
_ -> interpreterError p ("Invalid condition: " ++ show c')
-- lambda & application
eval (LmE p args e) = do
asks (FunV (foldr LambdaF (ExpF e) args))
eval (AppE p l r) = do
r' <- eval r
l' <- eval l
case l' of
-- left side must be a function
-- application "takes off" one variable from the lambda
FunV (LambdaF (Ident var) (ExpF exp)) env -> local (const $ insert var r' env) (eval exp)
FunV (LambdaF (Ident var) lm) env -> return $ FunV lm (insert var r' env)
_ -> interpreterError p ("Cannot apply (left: " ++ show l' ++ ") to (right: " ++ show r' ++ ").")
-- let
eval (LetE p ds e) = do
env <- ask
let (Right env') = execStateT (mapM_ declare ds) env
local (const env') (eval e)
-- lists
eval (LstE p exps) = do
exps' <- mapM eval exps
case (null exps', allInts exps', allBools exps') of
(True, _, _) -> return $ ListV EmptyList
(_, True, _) -> return $ ListV $ IntListV $ map (\(IntV n) -> n) exps'
(_, _, True) -> return $ ListV $ BoolListV $ map (\(BoolV b) -> b) exps'
_ -> interpreterError p ("Invalid list: " ++ show exps')
eval (ConE p e l) = do
l' <- eval l
e' <- eval e
case (e', l') of
(IntV e'', ListV (IntListV l'')) -> return $ ListV $ IntListV $ e'' : l''
(IntV e'', ListV EmptyList) -> return $ ListV $ IntListV [e'']
(BoolV e'', ListV (BoolListV l'')) -> return $ ListV $ BoolListV $ e'' : l''
(BoolV e'', ListV EmptyList) -> return $ ListV $ BoolListV [e'']
_ -> interpreterError p ("Cannot append " ++ show e' ++ " to " ++ show l' ++ ".")
-- builtin functions
eval (FunE p o e) = do
e' <- eval e
case e' of
ListV (IntListV l) -> case o of
Hd _ -> case l of
[] -> interpreterError p "Cannot get head of an empty list."
(x : _) -> return $ IntV x
Tl _ -> case l of
[] -> interpreterError p "Cannot get tail of an empty list."
(_ : xs) -> return $ ListV $ IntListV xs
Em _ -> return $ BoolV $ null l
ListV (BoolListV l) -> case o of
Hd _ -> case l of
[] -> interpreterError p "Cannot get head of an empty list."
(x : _) -> return $ BoolV x
Tl _ -> case l of
[] -> interpreterError p "Cannot get tail of an empty list."
(_ : xs) -> return $ ListV $ BoolListV xs
Em _ -> return $ BoolV $ null l
ListV EmptyList -> case o of
Hd _ -> interpreterError p "Cannot get head of an empty list."
Tl _ -> interpreterError p "Cannot get tail of an empty list."
Em _ -> return $ BoolV True
_ -> interpreterError p "Invalid list operation on a non-list."
declare :: Decl -> StateT Env Err ()
declare (FunD _ (Ident var) args exp) = do
env <- get
put $ insert var (FunV (foldr LambdaF (ExpF exp) args) env) env
initialEnv :: Env
initialEnv = empty
interpret :: Program -> Err Env
interpret (P _ ds) = execStateT (mapM_ declare ds) initialEnv
evalMain :: Env -> Err Value
evalMain env = case env !? "main" of
Just main -> case main of
FunV (ExpF exp) env' -> runReaderT (eval exp) env'
_ -> throwError "Main function incorrect - invalid declaration or parameterized."
Nothing -> throwError "Main function not found."