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module Haskell.Parser where
import Control.Monad
import Data.Char
import Haskell.AST
import Text.Parsec
import Text.Parsec.String
parseAST :: String -> String -> Either ParseError AST
parseAST fname source = parse pAST fname source
pAST :: Parser AST
pAST = do
whitespace
tops <- many pToplevel
eof
return $ AST tops
pToplevel :: Parser Toplevel
pToplevel = TopDef <$> pDef
pDef :: Parser Def
pDef = do
n <- pVariable
args <- many pNameV
symbolO "="
ex <- pExpr
symbolO ";"
case args of
[] -> return $ Def n ex
_ -> return $ Def n (Lam args ex)
pExpr :: Parser Expr
pExpr = pLam <|> pCase <|> pApp
where
pSimpleExpr = choice [Num <$> pNum
,Ref <$> pVariable
,Con <$> pNameT
,parens (pExpr `sepBy` symbolO ",") >>= \case
[ex] -> return ex
exs -> return $ Tup exs]
pLam = do
symbolO "\\"
args <- many1 pNameV
symbolO "->"
body <- pExpr
return $ Lam args body
pApp = many1 pSimpleExpr >>= \case
[] -> undefined
[e] -> return e
(e:es) -> return $ App e es
pCase = do
symbolW "case"
e <- pExpr
symbolW "of"
arms <- braces (pCaseArm `sepBy` symbolO ";")
return $ Case e arms
pCaseArm = do
pat <- pLargePat
symbolO "->"
ex <- pExpr
return (pat, ex)
pSimplePat :: Parser Pat
pSimplePat = choice [symbolW "_" >> return PatAny
,PatVar <$> pNameV
,pNameT >>= \n -> return (PatCon n [])
,parens (pLargePat `sepBy` symbolO ",") >>= \case
[pat] -> return pat
pats -> return $ PatTup pats]
pLargePat :: Parser Pat
pLargePat = choice [PatCon <$> pNameT <*> many pSimplePat
,pSimplePat]
pNum :: Parser Integer
pNum = (char '-' >> (negate <$> pPositive)) <|> pPositive
where pPositive = read <$> many1 digit <* aheadW
pVariable :: Parser Name
pVariable = pNameV <|> try (parens pOperator)
pName :: Parser Name
pName = notReserved $ liftM2 (:) (satisfy isAlpha) pNameRest
pNameV :: Parser Name
pNameV = notReserved $ liftM2 (:) (satisfy isLower) pNameRest
pNameT :: Parser Name
pNameT = notReserved $ liftM2 (:) (satisfy isUpper) pNameRest
pNameRest :: Parser Name
pNameRest = many (satisfy $ \d -> isAlphaNum d || d `elem` "_'") <* aheadW
notReserved :: Parser Name -> Parser Name
notReserved p =
try $ p >>= \n ->
if n `elem` reservedWords then unexpected "reserved word" else return n
pOperator :: Parser String
pOperator = many1 (oneOf ":!#$%&*+./<=>?@\\^|-~") <* aheadO
parens :: Parser a -> Parser a
parens = between (symbolBare "(") (symbolBare ")")
braces :: Parser a -> Parser a
braces = between (symbolBare "{") (symbolBare "}")
symbolW :: String -> Parser ()
symbolW s = try (string s >> aheadW)
symbolO :: String -> Parser ()
symbolO s = try (string s >> aheadO)
symbolBare :: String -> Parser ()
symbolBare s = string s >> whitespace
aheadW :: Parser ()
aheadW = do
void (lookAhead (space <|> satisfy (\d -> not (isAlphaNum d) && d `notElem` "_'"))) <|> eof
whitespace
aheadO :: Parser ()
aheadO = do
void (lookAhead (space <|> alphaNum <|> oneOf ")};")) <|> eof
whitespace
whitespace :: Parser ()
whitespace = void $ many space
reservedWords :: [String]
reservedWords = ["case", "of", "class", "instance", "where", "let", "in"]
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