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module DSL.BaseParsers where
-- Parsec is for casuals
import Control.Applicative (Alternative(..), liftA2)
import Control.Monad (MonadPlus(..), guard)
import Data.Maybe (catMaybes)
import Data.Void
data ParserError
= ErrorLeaf String
| ErrorBranch String [ParserError]
deriving (Show)
newtype Parser t a =
Parser { parse :: [t] -> Either ParserError ([t], a) }
instance Semigroup a => Semigroup (Parser t a) where
(<>) = liftA2 (<>)
instance Monoid a => Monoid (Parser t a) where
mempty = pure mempty
instance Functor (Parser t) where
fmap f (Parser p) = Parser $ fmap (fmap f) . p
instance Applicative (Parser t) where
pure = result
p <*> q = Parser $ \ inp -> do
(inp', f) <- parse p inp
parse (f <$> q) inp'
instance Monad (Parser t) where
return = pure
p >>= f = Parser $ \ inp -> do
(inp', x) <- parse p inp
parse (f x) inp'
instance Alternative (Parser t) where
empty = flunkWith "Flunked: empty Alternative"
(<|>) = alt
instance MonadPlus (Parser t)
instance MonadFail (Parser t) where
fail _ = mzero
type ErrorChanger t a = String -> Parser t a -> Parser t a
nicePrintParserError :: ParserError -> String
nicePrintParserError = unlines . go 0
where
indentSize = 4
go indent (ErrorLeaf s) = [replicate indent ' ' ++ s]
go indent (ErrorBranch s es) = s':es'
where
s' = replicate indent ' ' ++ s
es' = es >>= go (indent + indentSize)
-----------------------------------------------------------------------------
perr :: String -> Either ParserError Void
perr = Left . ErrorLeaf
overwriteError :: ErrorChanger t a
overwriteError s p = Parser $ \ inp -> case parse p inp of
Left _ -> absurd <$> perr s
Right x -> Right x
setError :: ErrorChanger t a
setError s p = Parser $ \ inp -> case parse p inp of
Left (ErrorLeaf _) -> absurd <$> perr s
Left (ErrorBranch _ es) -> Left $ ErrorBranch s es
Right x -> Right x
prependError :: ErrorChanger t a
prependError s p = Parser $ \ inp -> case parse p inp of
Left e -> Left $ ErrorBranch s [e]
Right x -> Right x
flunk :: Parser t a
flunk = flunkWith "Flunked parser"
flunkWith :: String -> Parser t a
flunkWith e = Parser $ \ _ -> absurd <$> perr e
result :: a -> Parser t a
result x = Parser $ \ inp -> Right (inp, x)
peek :: Parser t a -> Parser t a
peek p = prependError "peek:" $ Parser $ \ inp -> do
(_, x) <- parse p inp
return (inp, x)
anyToken :: Parser t t
anyToken = Parser $ \ inp -> case inp of
t:ts -> Right (ts, t)
_ -> absurd <$> perr "anyToken: Expected a token, got EOF"
eof :: Parser t ()
eof = Parser $ \ inp -> case inp of
[] -> Right ([], ())
_ -> absurd <$> perr "eof: Expected EOF, got a token"
infixl 3 `alt`
alt :: Parser t a -> Parser t a -> Parser t a
alt p q = Parser $ \ inp -> case (parse p inp, parse q inp) of
(Right x, _) -> Right x
(_, Right x) -> Right x
(Left e1, Left e2) -> Left $ case (e1, e2) of
(ErrorLeaf s, ErrorBranch b es) -> ErrorBranch b (ErrorLeaf s:es)
(ErrorBranch b es, ErrorLeaf s) -> ErrorBranch b (es ++ [ErrorLeaf s])
_ -> ErrorBranch "alt:" [e1, e2]
chain :: Parser s [t] -> Parser t a -> Parser s a
chain p q = prependError "chain:" $ Parser $ \ inp1 -> case parse p inp1 of
Left e1 -> Left e1
Right (inp1', inp2) -> case parse q inp2 of
Left e2 -> Left e2
Right (_, x) -> Right (inp1', x)
-----------------------------------------------------------------------------
phrase :: Parser t a -> Parser t a
phrase = prependError "phrase:" . (<* eof)
plus :: Parser t a -> Parser t b -> Parser t (a, b)
plus p q = prependError "plus:" $ liftA2 (,) p q
recover :: a -> Parser t a -> Parser t a
recover x p = p <|> pure x
optionalMaybe :: Parser t a -> Parser t (Maybe a)
optionalMaybe = recover Nothing . fmap Just
optionalEither :: e -> Parser t a -> Parser t (Either e a)
optionalEither e = recover (Left e) . fmap Right
optional :: Parser t a -> Parser t ()
optional p = () <$ optionalMaybe p
assert :: (a -> Bool) -> Parser t a -> Parser t a
assert f p = prependError "assert:" $ do
x <- p
guard $ f x
return x
satisfy :: (t -> Bool) -> Parser t t
satisfy f = prependError "satisfy:" $ assert f anyToken
token :: Eq t => t -> Parser t t
token t = prependError "token:" $ satisfy (==t)
list :: Eq t => [t] -> Parser t [t]
list = prependError "list:" . traverse token
mult :: Parser t a -> Parser t [a]
mult = prependError "mult:" . many
mult1 :: Parser t a -> Parser t [a]
mult1 = prependError "mult1:" . some
exactly :: Int -> Parser t a -> Parser t [a]
exactly i = prependError "exactly:" . sequence . replicate i
atLeast :: Int -> Parser t a -> Parser t [a]
atLeast i p = prependError "atLeast:" $ exactly i p <> mult p
atMost :: Int -> Parser t a -> Parser t [a]
atMost i = prependError "atMost" . fmap catMaybes . exactly i . optionalMaybe
between :: Int -> Int -> Parser t a -> Parser t [a]
between x y p = prependError "between:" $ exactly (min x y) p <> atMost (abs $ x - y) p
stopAt :: Parser t a -> Parser t [t]
stopAt p = setError "stopAt: failed to find stop point" $ go
where
p' = ([] <$ peek p)
go = p' <|> liftA2 (:) anyToken go
stopAfter :: Parser t a -> Parser t ([t], a)
stopAfter p = prependError "stopAfter:" $ stopAt p `plus` p
stopIf :: Parser t a -> Parser t [t]
stopIf p = stopAt $ () <$ p <|> eof
firstOf :: [Parser t a] -> Parser t a
firstOf = prependError "firstOf:" . foldr1 (<|>)
sepBy1 :: Parser t a -> Parser t b -> Parser t [a]
sepBy1 a b = prependError "sepBy1:" $ do
x <- a
xs <- mult $ b >> a
return $ x:xs
sepBy :: Parser t a -> Parser t b -> Parser t [a]
sepBy a b = sepBy1 a b <|> pure []
|
