Text.Megaparsec.Error

Parse errors. Current version of Megaparsec supports well-typed errors instead of String-based ones. This gives a lot of flexibility in describing what exactly went wrong as well as a way to return arbitrary data in case of failure.

Documentation

data ErrorItem t

Data type that is used to represent “unexpected/expected” items in parse error. The data type is parametrized over token type t.

Since: 5.0.0

Constructors

Tokens (NonEmpty t)

Non-empty stream of tokens

Label (NonEmpty Char)

Label (cannot be empty)

EndOfInput

End of input

Instances

Eq t => Eq (ErrorItem t)

Methods

(==) :: ErrorItem t -> ErrorItem t -> Bool

(/=) :: ErrorItem t -> ErrorItem t -> Bool

Data t => Data (ErrorItem t)

Methods

gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> ErrorItem t -> c (ErrorItem t)

gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c (ErrorItem t)

toConstr :: ErrorItem t -> Constr

dataTypeOf :: ErrorItem t -> DataType

dataCast1 :: Typeable (* -> *) t => (forall d. Data d => c (t d)) -> Maybe (c (ErrorItem t))

dataCast2 :: Typeable (* -> * -> *) t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c (ErrorItem t))

gmapT :: (forall b. Data b => b -> b) -> ErrorItem t -> ErrorItem t

gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> ErrorItem t -> r

gmapQr :: (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> ErrorItem t -> r

gmapQ :: (forall d. Data d => d -> u) -> ErrorItem t -> [u]

gmapQi :: Int -> (forall d. Data d => d -> u) -> ErrorItem t -> u

gmapM :: Monad m => (forall d. Data d => d -> m d) -> ErrorItem t -> m (ErrorItem t)

gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> ErrorItem t -> m (ErrorItem t)

gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> ErrorItem t -> m (ErrorItem t)

Ord t => Ord (ErrorItem t)

Methods

compare :: ErrorItem t -> ErrorItem t -> Ordering

(<) :: ErrorItem t -> ErrorItem t -> Bool

(<=) :: ErrorItem t -> ErrorItem t -> Bool

(>) :: ErrorItem t -> ErrorItem t -> Bool

(>=) :: ErrorItem t -> ErrorItem t -> Bool

max :: ErrorItem t -> ErrorItem t -> ErrorItem t

min :: ErrorItem t -> ErrorItem t -> ErrorItem t

Read t => Read (ErrorItem t)

Methods

readsPrec :: Int -> ReadS (ErrorItem t)

readList :: ReadS [ErrorItem t]

readPrec :: ReadPrec (ErrorItem t)

readListPrec :: ReadPrec [ErrorItem t]

Show t => Show (ErrorItem t)

Methods

showsPrec :: Int -> ErrorItem t -> ShowS

show :: ErrorItem t -> String

showList :: [ErrorItem t] -> ShowS

Generic (ErrorItem t)

Associated Types

type Rep (ErrorItem t) :: * -> *

Methods

from :: ErrorItem t -> Rep (ErrorItem t) x

to :: Rep (ErrorItem t) x -> ErrorItem t

Arbitrary t => Arbitrary (ErrorItem t)

Methods

arbitrary :: Gen (ErrorItem t)

shrink :: ErrorItem t -> [ErrorItem t]

NFData t => NFData (ErrorItem t)

Methods

rnf :: ErrorItem t -> ()

(Ord t, ShowToken t) => ShowErrorComponent (ErrorItem t)

Methods

showErrorComponent :: ErrorItem t -> String

type Rep (ErrorItem t)

type Rep (ErrorItem t) = D1 (MetaData "ErrorItem" "Text.Megaparsec.Error" "megaparsec-5.2.0-5Nnt0uqxGq2A3FwuKIsIs3" False) ((:+:) (C1 (MetaCons "Tokens" PrefixI False) (S1 (MetaSel (Nothing Symbol) NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 (NonEmpty t)))) ((:+:) (C1 (MetaCons "Label" PrefixI False) (S1 (MetaSel (Nothing Symbol) NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 (NonEmpty Char)))) (C1 (MetaCons "EndOfInput" PrefixI False) U1)))

class Ord e => ErrorComponent e where

The type class defines how to represent information about various exceptional situations. Data types that are used as custom data component in ParseError must be instances of this type class.

Since: 5.0.0

Minimal complete definition

representFail, representIndentation

Methods

representFail :: String -> e

Represent message passed to fail in parser monad.

Since: 5.0.0

representIndentation :: Ordering -> Pos -> Pos -> e

Represent information about incorrect indentation.

Since: 5.0.0

Instances

ErrorComponent Dec

Methods

representFail :: String -> Dec

representIndentation :: Ordering -> Pos -> Pos -> Dec

data Dec

“Default error component”. This in our instance of ErrorComponent provided out-of-box.

Since: 5.0.0

Constructors

DecFail String

fail has been used in parser monad

DecIndentation Ordering Pos Pos

Incorrect indentation error: desired ordering between reference level and actual level, reference indentation level, actual indentation level

Instances

Eq Dec

Methods

(==) :: Dec -> Dec -> Bool

(/=) :: Dec -> Dec -> Bool

Data Dec

Methods

gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> Dec -> c Dec

gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c Dec

toConstr :: Dec -> Constr

dataTypeOf :: Dec -> DataType

dataCast1 :: Typeable (* -> *) t => (forall d. Data d => c (t d)) -> Maybe (c Dec)

dataCast2 :: Typeable (* -> * -> *) t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c Dec)

gmapT :: (forall b. Data b => b -> b) -> Dec -> Dec

gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> Dec -> r

gmapQr :: (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> Dec -> r

gmapQ :: (forall d. Data d => d -> u) -> Dec -> [u]

gmapQi :: Int -> (forall d. Data d => d -> u) -> Dec -> u

gmapM :: Monad m => (forall d. Data d => d -> m d) -> Dec -> m Dec

gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> Dec -> m Dec

gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> Dec -> m Dec

Ord Dec

Methods

compare :: Dec -> Dec -> Ordering

(<) :: Dec -> Dec -> Bool

(<=) :: Dec -> Dec -> Bool

(>) :: Dec -> Dec -> Bool

(>=) :: Dec -> Dec -> Bool

max :: Dec -> Dec -> Dec

min :: Dec -> Dec -> Dec

Read Dec

Methods

readsPrec :: Int -> ReadS Dec

readList :: ReadS [Dec]

readPrec :: ReadPrec Dec

readListPrec :: ReadPrec [Dec]

Show Dec

Methods

showsPrec :: Int -> Dec -> ShowS

show :: Dec -> String

showList :: [Dec] -> ShowS

Arbitrary Dec

Methods

arbitrary :: Gen Dec

shrink :: Dec -> [Dec]

NFData Dec

Methods

rnf :: Dec -> ()

ShowErrorComponent Dec

Methods

showErrorComponent :: Dec -> String

ErrorComponent Dec

Methods

representFail :: String -> Dec

representIndentation :: Ordering -> Pos -> Pos -> Dec

data ParseError t e

The data type ParseError represents parse errors. It provides the stack of source positions, set of expected and unexpected tokens as well as set of custom associated data. The data type is parametrized over token type t and custom data e.

Note that stack of source positions contains current position as its head, and the rest of positions allows to track full sequence of include files with topmost source file at the end of the list.

Semigroup (or Monoid) instance of the data type allows to merge parse errors from different branches of parsing. When merging two ParseErrors, longest match is preferred; if positions are the same, custom data sets and collections of message items are combined.

Constructors

ParseError

Fields

• errorPos :: NonEmpty SourcePos

  Stack of source positions

• errorUnexpected :: Set (ErrorItem t)

  Unexpected items

• errorExpected :: Set (ErrorItem t)

  Expected items

• errorCustom :: Set e

  Associated data, if any

Instances

(Eq e, Eq t) => Eq (ParseError t e)

Methods

(==) :: ParseError t e -> ParseError t e -> Bool

(/=) :: ParseError t e -> ParseError t e -> Bool

(Ord e, Ord t, Data e, Data t) => Data (ParseError t e)

Methods

gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> ParseError t e -> c (ParseError t e)

gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c (ParseError t e)

toConstr :: ParseError t e -> Constr

dataTypeOf :: ParseError t e -> DataType

dataCast1 :: Typeable (* -> *) t => (forall d. Data d => c (t d)) -> Maybe (c (ParseError t e))

dataCast2 :: Typeable (* -> * -> *) t => (forall d a. (Data d, Data a) => c (t d a)) -> Maybe (c (ParseError t e))

gmapT :: (forall b. Data b => b -> b) -> ParseError t e -> ParseError t e

gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> ParseError t e -> r

gmapQr :: (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> ParseError t e -> r

gmapQ :: (forall d. Data d => d -> u) -> ParseError t e -> [u]

gmapQi :: Int -> (forall d. Data d => d -> u) -> ParseError t e -> u

gmapM :: Monad m => (forall d. Data d => d -> m d) -> ParseError t e -> m (ParseError t e)

gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> ParseError t e -> m (ParseError t e)

gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> ParseError t e -> m (ParseError t e)

(Ord e, Ord t, Read e, Read t) => Read (ParseError t e)

Methods

readsPrec :: Int -> ReadS (ParseError t e)

readList :: ReadS [ParseError t e]

readPrec :: ReadPrec (ParseError t e)

readListPrec :: ReadPrec [ParseError t e]

(Show e, Show t) => Show (ParseError t e)

Methods

showsPrec :: Int -> ParseError t e -> ShowS

show :: ParseError t e -> String

showList :: [ParseError t e] -> ShowS

Generic (ParseError t e)

Associated Types

type Rep (ParseError t e) :: * -> *

Methods

from :: ParseError t e -> Rep (ParseError t e) x

to :: Rep (ParseError t e) x -> ParseError t e

(Ord t, Ord e) => Semigroup (ParseError t e)

Methods

(<>) :: ParseError t e -> ParseError t e -> ParseError t e

sconcat :: NonEmpty (ParseError t e) -> ParseError t e

stimes :: Integral b => b -> ParseError t e -> ParseError t e

(Ord t, Ord e) => Monoid (ParseError t e)

Methods

mempty :: ParseError t e

mappend :: ParseError t e -> ParseError t e -> ParseError t e

mconcat :: [ParseError t e] -> ParseError t e

(Arbitrary t, Ord t, Arbitrary e, Ord e) => Arbitrary (ParseError t e)

Methods

arbitrary :: Gen (ParseError t e)

shrink :: ParseError t e -> [ParseError t e]

(Show t, Typeable * t, Ord t, ShowToken t, Show e, Typeable * e, ShowErrorComponent e) => Exception (ParseError t e)

Methods

toException :: ParseError t e -> SomeException

fromException :: SomeException -> Maybe (ParseError t e)

displayException :: ParseError t e -> String

(NFData t, NFData e) => NFData (ParseError t e)

Methods

rnf :: ParseError t e -> ()

type Rep (ParseError t e)

type Rep (ParseError t e) = D1 (MetaData "ParseError" "Text.Megaparsec.Error" "megaparsec-5.2.0-5Nnt0uqxGq2A3FwuKIsIs3" False) (C1 (MetaCons "ParseError" PrefixI True) ((:*:) ((:*:) (S1 (MetaSel (Just Symbol "errorPos") NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 (NonEmpty SourcePos))) (S1 (MetaSel (Just Symbol "errorUnexpected") NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 (Set (ErrorItem t))))) ((:*:) (S1 (MetaSel (Just Symbol "errorExpected") NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 (Set (ErrorItem t)))) (S1 (MetaSel (Just Symbol "errorCustom") NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 (Set e))))))

class ShowToken a where

Type class ShowToken includes methods that allow to pretty-print single token as well as stream of tokens. This is used for rendering of error messages.

Minimal complete definition

showTokens

Methods

showTokens :: NonEmpty a -> String

Pretty-print non-empty stream of tokens. This function is also used to print single tokens (represented as singleton lists).

Since: 5.0.0

Instances

ShowToken Char

Methods

showTokens :: NonEmpty Char -> String

class Ord a => ShowErrorComponent a where

The type class defines how to print custom data component of ParseError.

Since: 5.0.0

Minimal complete definition

showErrorComponent

Methods

showErrorComponent :: a -> String

Pretty-print custom data component of ParseError.

Instances

ShowErrorComponent Dec

Methods

showErrorComponent :: Dec -> String

(Ord t, ShowToken t) => ShowErrorComponent (ErrorItem t)

Methods

showErrorComponent :: ErrorItem t -> String

parseErrorPretty

Arguments

:: (Ord t, ShowToken t, ShowErrorComponent e)

=> ParseError t e

Parse error to render

-> String

Result of rendering

Pretty-print ParseError. The rendered String always ends with a newline.

The function is defined as:

parseErrorPretty e =
  sourcePosStackPretty (errorPos e) ++ ":\n" ++ parseErrorTextPretty e

Since: 5.0.0

sourcePosStackPretty :: NonEmpty SourcePos -> String

Pretty-print stack of source positions.

Since: 5.0.0

parseErrorTextPretty

Arguments

:: (Ord t, ShowToken t, ShowErrorComponent e)

=> ParseError t e

Parse error to render

-> String

Result of rendering

Pretty-print textual part of a ParseError, that is, everything except stack of source positions. The rendered staring always ends with a new line.

Since: 5.1.0