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|
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE TupleSections #-}
module Language.SimpleShell.Parser.Expr
( exprP
, strongTermP
, strongTermP_ -- TODO: Unused.
)
where
import Language.SimpleShell.AST.Expr (Expr(..), TypedExpr)
import Language.SimpleShell.AST.SimpleType (SimpleType(..))
import Language.SimpleShell.Parser
( Parser
, lexeme
, symbol
, lookupVar
, lookupFun
)
import Language.SimpleShell.Parser.Name (nameP, keyword)
import Language.SimpleShell.Parser.SimpleType (forceType)
import Control.Monad.Combinators.FailExpr
( Associativity(..)
, makeExprParser
, Operator(..)
)
import Control.Applicative ((<|>))
import Control.Monad (void)
import Control.Monad.Combinators (manyTill)
import Data.Foldable (asum)
import Data.Text (Text)
import Text.Megaparsec (anySingleBut, many)
import Text.Megaparsec.Char (char)
import qualified Text.Megaparsec.Char.Lexer as L (charLiteral, decimal)
exprP :: Parser TypedExpr
exprP
= makeExprParser weakTermP binaryOperatorTable
weakTermP :: Parser TypedExpr
weakTermP
= strongTermP
<|> unaryOpP
<|> builtinUnaryFunP
<|> funP
strongTermP :: Parser TypedExpr
strongTermP
= literalP
<|> varP
<|> symbol "(" *> exprP <* symbol ")"
-- | Parse a strong term--assuming its correctness--without yielding a result.
-- This basically only checks for matching parentheses.
strongTermP_ :: Parser ()
strongTermP_
= void literalP
<|> varP_
<|> symbol "(" *> void (many tok) <* symbol ")"
where
-- Notes:
-- * We need to make sure to correctly handle:
-- * parentheses
-- * string literals
-- * comments
-- - Thus, `takeWhile1P` is dangerous.
-- * This is hardly the most efficient implementation.
-- * A more efficient implementation would use `takeWhile1P` to parse
-- large chunks of input, but--as noted above--that is dangerous;
-- i.e., non-trivial (albeit not really hard) to do correctly.
tok :: Parser ()
tok
= strongTermP_
<|> void nameP -- function names; for efficiency only
<|> void (lexeme $ anySingleBut ')') -- operators (i.a.; catchall)
-- | Parse "strong" term with fixed type.
strongTermP' :: String -> SimpleType -> Parser Expr
strongTermP' errMsg t = forceType t strongTermP <|> fail errMsg
literalP :: Parser TypedExpr
literalP
= (IntType,) . IntLiteral <$> lexeme L.decimal
<|> (StrType,) . StrLiteral <$> strLitP
<|> (BoolType,) . BoolLiteral <$> boolLitP
where
boolLitP
= True <$ keyword "true"
<|> False <$ keyword "false"
strLitP :: Parser String
strLitP = lexeme $ char '"' *> manyTill L.charLiteral (char '"')
varP :: Parser TypedExpr
varP = do
_ <- char '$'
x <- nameP
t <- lookupVar x
return (t, Var x)
varP_ :: Parser ()
varP_ = void (char '$') <* nameP
funP :: Parser TypedExpr
funP = do
fname <- nameP
(t', ts) <- lookupFun fname
args <- mapM (strongTermP' "Type mismatch with function signature.") ts
return (t', FunCall fname args)
-- Binary operators.
type BinaryFun = Expr -> Expr -> Expr
type BinarySig = SimpleType -> SimpleType -> Maybe SimpleType
binaryOperatorTable :: [[Operator Parser TypedExpr]]
binaryOperatorTable =
[ [ binary AssocR "||" Or $ sameSig BoolType
]
, [ binary AssocR "&&" And $ sameSig BoolType
]
, [ binary AssocN "==" Eq $ anyCmpSig
, binary AssocN "!=" Neq $ anyCmpSig
, binary AssocN "<=" Le $ intCmpSig
, binary AssocN "<" Lt $ intCmpSig
, binary AssocN ">=" Ge $ intCmpSig
, binary AssocN ">" Gt $ intCmpSig
]
, [ Binary AssocL addP
, binary AssocL "-" Sub $ sameSig IntType
]
, [ binary AssocL "*" Mul $ sameSig IntType
, binary AssocL "/" Div $ sameSig IntType
]
]
where
sameSig :: SimpleType -> BinarySig
sameSig t t1 t2 = if t == t1 && t == t2 then Just t else Nothing
anyCmpSig t t'
| t == t' = Just BoolType
| otherwise = Nothing
intCmpSig IntType IntType = Just BoolType
intCmpSig _ _ = Nothing
addP :: Parser (TypedExpr -> TypedExpr -> Maybe TypedExpr)
addP = do
symbol "+"
return $ \(t1, x1) (t2, x2) ->
if t1 == t2
then
case t1 of
StrType -> Just (StrType, Concat x1 x2)
IntType -> Just (IntType, Add x1 x2)
_ -> Nothing
else Nothing
binary
:: Associativity -> Text -> BinaryFun -> BinarySig
-> Operator Parser TypedExpr
binary assoc symb op sig = Binary assoc $ do
symbol symb
return $ \(t1, e1) (t2, e2) -> fmap (, op e1 e2) $ sig t1 t2
-- Unary operators and builtin unary functions.
type UnaryFun = Expr -> Expr
type UnarySig = SimpleType -> Maybe SimpleType
type UnaryParser = Parser (TypedExpr -> Maybe TypedExpr)
unaryOperators, builtinUnaryFuns :: [UnaryParser]
(unaryOperators, builtinUnaryFuns) =
( [ unaryOp "!" Not $ uniqueSig BoolType BoolType
, unaryOp "-" UMinus $ uniqueSig IntType IntType
]
, [ unaryFun "length" Length $ uniqueSig StrType IntType
, unaryFun "int" IntCast $ uniqueSig StrType IntType
, unaryFun "str" StrCast $ uniqueSig IntType StrType
]
)
where
uniqueSig :: SimpleType -> SimpleType -> UnarySig
uniqueSig t1 t2 t1'
| t1 == t1' = Just t2
| otherwise = Nothing
unaryOp :: Text -> UnaryFun -> UnarySig -> UnaryParser
unaryOp = unary symbol
unaryFun :: Text -> UnaryFun -> UnarySig -> UnaryParser
unaryFun = unary keyword
unary :: (Text -> Parser ()) -> Text -> UnaryFun -> UnarySig -> UnaryParser
unary symbPF symb op sig = do
symbPF symb
return $ \(t, e) -> fmap (, op e) $ sig t
unaryOpP, builtinUnaryFunP :: Parser TypedExpr
(unaryOpP, builtinUnaryFunP) =
( asum $ map (aux "unary operator" weakTermP ) unaryOperators
, asum $ map (aux "builtin unary function" strongTermP) builtinUnaryFuns
)
where
aux :: String -> Parser TypedExpr -> UnaryParser -> Parser TypedExpr
aux desc argP p = do
f <- p
x <- argP
case f x of
Just x' -> return x'
Nothing -> fail $ "Mismatching " ++ desc ++ " signature."
|
