Copyright	© 2015–2017 Megaparsec contributors
License	FreeBSD
Maintainer	Mark Karpov <markkarpov92@gmail.com>
Stability	experimental
Portability	portable
Safe Haskell	None
Language	Haskell2010

Text.Megaparsec.Error

Contents

Parse error type
Pretty-printing

Description

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.

You probably do not want to import this module directly because Text.Megaparsec re-exports it anyway.

Synopsis

Parse error type

data ErrorItem t Source #

Data type that is used to represent “unexpected/expected” items in ParseError. The data type is parametrized over the 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

Functor ErrorItem Source #
Methods fmap :: (a -> b) -> ErrorItem a -> ErrorItem b # (<$) :: a -> ErrorItem b -> ErrorItem a #
Eq t => Eq (ErrorItem t) Source #
Methods (==) :: ErrorItem t -> ErrorItem t -> Bool # (/=) :: ErrorItem t -> ErrorItem t -> Bool #
Data t => Data (ErrorItem t) Source #
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) Source #
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) Source #
Methods readsPrec :: Int -> ReadS (ErrorItem t) # readList :: ReadS [ErrorItem t] # readPrec :: ReadPrec (ErrorItem t) # readListPrec :: ReadPrec [ErrorItem t] #
Show t => Show (ErrorItem t) Source #
Methods showsPrec :: Int -> ErrorItem t -> ShowS # show :: ErrorItem t -> String # showList :: [ErrorItem t] -> ShowS #
Generic (ErrorItem t) Source #
Associated Types type Rep (ErrorItem t) :: * -> * # Methods from :: ErrorItem t -> Rep (ErrorItem t) x # to :: Rep (ErrorItem t) x -> ErrorItem t #
NFData t => NFData (ErrorItem t) Source #
Methods rnf :: ErrorItem t -> () #
(Ord t, ShowToken t) => ShowErrorComponent (ErrorItem t) Source #
Methods showErrorComponent :: ErrorItem t -> String Source #
type Rep (ErrorItem t) Source #
type Rep (ErrorItem t) = D1 * (MetaData "ErrorItem" "Text.Megaparsec.Error" "megaparsec-6.4.0-xl4HlJBghw88uZEZB1lRf" 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 *))))

data ErrorFancy e Source #

Additional error data, extendable by user. When no custom data is necessary, the type is typically indexed by Void to “cancel” the ErrorCustom constructor.

Since: 6.0.0

Constructors

ErrorFail String	`fail` has been used in parser monad
ErrorIndentation Ordering Pos Pos	Incorrect indentation error: desired ordering between reference level and actual level, reference indentation level, actual indentation level
ErrorCustom e	Custom error data, can be conveniently disabled by indexing `ErrorFancy` by `Void`

Instances

Functor ErrorFancy Source #
Methods fmap :: (a -> b) -> ErrorFancy a -> ErrorFancy b # (<$) :: a -> ErrorFancy b -> ErrorFancy a #
Eq e => Eq (ErrorFancy e) Source #
Methods (==) :: ErrorFancy e -> ErrorFancy e -> Bool # (/=) :: ErrorFancy e -> ErrorFancy e -> Bool #
Data e => Data (ErrorFancy e) Source #
Methods gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> ErrorFancy e -> c (ErrorFancy e) # gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c (ErrorFancy e) # toConstr :: ErrorFancy e -> Constr # dataTypeOf :: ErrorFancy e -> DataType # dataCast1 :: Typeable (* -> ) t => (forall d. Data d => c (t d)) -> Maybe (c (ErrorFancy e)) # dataCast2 :: Typeable ( -> * -> *) t => (forall d a. (Data d, Data a) => c (t d a)) -> Maybe (c (ErrorFancy e)) # gmapT :: (forall b. Data b => b -> b) -> ErrorFancy e -> ErrorFancy e # gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> ErrorFancy e -> r # gmapQr :: (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> ErrorFancy e -> r # gmapQ :: (forall d. Data d => d -> u) -> ErrorFancy e -> [u] # gmapQi :: Int -> (forall d. Data d => d -> u) -> ErrorFancy e -> u # gmapM :: Monad m => (forall d. Data d => d -> m d) -> ErrorFancy e -> m (ErrorFancy e) # gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> ErrorFancy e -> m (ErrorFancy e) # gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> ErrorFancy e -> m (ErrorFancy e) #
Ord e => Ord (ErrorFancy e) Source #
Methods compare :: ErrorFancy e -> ErrorFancy e -> Ordering # (<) :: ErrorFancy e -> ErrorFancy e -> Bool # (<=) :: ErrorFancy e -> ErrorFancy e -> Bool # (>) :: ErrorFancy e -> ErrorFancy e -> Bool # (>=) :: ErrorFancy e -> ErrorFancy e -> Bool # max :: ErrorFancy e -> ErrorFancy e -> ErrorFancy e # min :: ErrorFancy e -> ErrorFancy e -> ErrorFancy e #
Read e => Read (ErrorFancy e) Source #
Methods readsPrec :: Int -> ReadS (ErrorFancy e) # readList :: ReadS [ErrorFancy e] # readPrec :: ReadPrec (ErrorFancy e) # readListPrec :: ReadPrec [ErrorFancy e] #
Show e => Show (ErrorFancy e) Source #
Methods showsPrec :: Int -> ErrorFancy e -> ShowS # show :: ErrorFancy e -> String # showList :: [ErrorFancy e] -> ShowS #
Generic (ErrorFancy e) Source #
Associated Types type Rep (ErrorFancy e) :: * -> * # Methods from :: ErrorFancy e -> Rep (ErrorFancy e) x # to :: Rep (ErrorFancy e) x -> ErrorFancy e #
NFData a => NFData (ErrorFancy a) Source #
Methods rnf :: ErrorFancy a -> () #
ShowErrorComponent e => ShowErrorComponent (ErrorFancy e) Source #
Methods showErrorComponent :: ErrorFancy e -> String Source #
type Rep (ErrorFancy e) Source #
type Rep (ErrorFancy e) = D1 * (MetaData "ErrorFancy" "Text.Megaparsec.Error" "megaparsec-6.4.0-xl4HlJBghw88uZEZB1lRf" False) ((:+:) * (C1 * (MetaCons "ErrorFail" PrefixI False) (S1 * (MetaSel (Nothing Symbol) NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 * String))) ((:+:) * (C1 * (MetaCons "ErrorIndentation" PrefixI False) ((::) (S1 * (MetaSel (Nothing Symbol) NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 * Ordering)) ((::) (S1 * (MetaSel (Nothing Symbol) NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 * Pos)) (S1 * (MetaSel (Nothing Symbol) NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 * Pos))))) (C1 * (MetaCons "ErrorCustom" PrefixI False) (S1 * (MetaSel (Nothing Symbol) NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 * e)))))

data ParseError t e Source #

ParseError t e represents a parse error parametrized over the token type t and the custom data e.

Note that the 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 and Monoid instances of the data type allow to merge parse errors from different branches of parsing. When merging two ParseErrors, the longest match is preferred; if positions are the same, custom data sets and collections of message items are combined. Note that fancy errors take precedence over trivial errors in merging.

Since: 6.0.0

Constructors

TrivialError (NonEmpty SourcePos) (Maybe (ErrorItem t)) (Set (ErrorItem t))	Trivial errors, generated by Megaparsec's machinery. The data constructor includes the stack of source positions, unexpected token (if any), and expected tokens.
FancyError (NonEmpty SourcePos) (Set (ErrorFancy e))	Fancy, custom errors.

Instances

(Eq e, Eq t) => Eq (ParseError t e) Source #
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) Source #
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) Source #
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) Source #
Methods showsPrec :: Int -> ParseError t e -> ShowS # show :: ParseError t e -> String # showList :: [ParseError t e] -> ShowS #
Generic (ParseError t e) Source #
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) Source #
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) Source #
Methods mempty :: ParseError t e # mappend :: ParseError t e -> ParseError t e -> ParseError t e # mconcat :: [ParseError t e] -> ParseError t e #
(Show t, Ord t, ShowToken t, Typeable * t, Show e, ShowErrorComponent e, Typeable * e) => Exception (ParseError t e) Source #
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) Source #
Methods rnf :: ParseError t e -> () #
type Rep (ParseError t e) Source #
type Rep (ParseError t e) = D1 * (MetaData "ParseError" "Text.Megaparsec.Error" "megaparsec-6.4.0-xl4HlJBghw88uZEZB1lRf" False) ((:+:) * (C1 * (MetaCons "TrivialError" PrefixI False) ((::) (S1 * (MetaSel (Nothing Symbol) NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 * (NonEmpty SourcePos))) ((::) (S1 * (MetaSel (Nothing Symbol) NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 * (Maybe (ErrorItem t)))) (S1 * (MetaSel (Nothing Symbol) NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 * (Set (ErrorItem t))))))) (C1 * (MetaCons "FancyError" PrefixI False) ((::) (S1 * (MetaSel (Nothing Symbol) NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 * (NonEmpty SourcePos))) (S1 * (MetaSel (Nothing Symbol) NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 * (Set (ErrorFancy e)))))))

errorPos :: ParseError t e -> NonEmpty SourcePos Source #

Get position of given ParseError.

Since: 6.0.0

Pretty-printing

class ShowToken a where Source #

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.

Since: 5.0.0

Minimal complete definition

showTokens

Methods

showTokens :: NonEmpty a -> String Source #

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

Instances

ShowToken Char Source #
Methods showTokens :: NonEmpty Char -> String Source #
ShowToken Word8 Source #
Methods showTokens :: NonEmpty Word8 -> String Source #

class LineToken a where Source #

Type class for tokens that support operations necessary for selecting and displaying relevant line of input.

Since: 6.0.0

Minimal complete definition

tokenAsChar, tokenIsNewline

Methods

tokenAsChar :: a -> Char Source #

Convert a token to a Char. This is used to print relevant line from input stream by turning a list of tokens into a String.

tokenIsNewline :: a -> Bool Source #

Check if given token is a newline or contains newline.

Instances

LineToken Char Source #
Methods tokenAsChar :: Char -> Char Source # tokenIsNewline :: Char -> Bool Source #
LineToken Word8 Source #
Methods tokenAsChar :: Word8 -> Char Source # tokenIsNewline :: Word8 -> Bool Source #

class Ord a => ShowErrorComponent a where Source #

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

Since: 5.0.0

Minimal complete definition

showErrorComponent

Methods

showErrorComponent :: a -> String Source #

Pretty-print custom data component of ParseError.

Instances

ShowErrorComponent Void Source #
Methods showErrorComponent :: Void -> String Source #
ShowErrorComponent e => ShowErrorComponent (ErrorFancy e) Source #
Methods showErrorComponent :: ErrorFancy e -> String Source #
(Ord t, ShowToken t) => ShowErrorComponent (ErrorItem t) Source #
Methods showErrorComponent :: ErrorItem t -> String Source #

parseErrorPretty Source #

Arguments

:: (Ord t, ShowToken t, ShowErrorComponent e)
=> ParseError t e	Parse error to render
-> String	Result of rendering

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

Since: 5.0.0

parseErrorPretty' Source #

Arguments

:: (ShowToken (Token s), LineToken (Token s), ShowErrorComponent e, Stream s)
=> s	Original input stream
-> ParseError (Token s) e	Parse error to render
-> String	Result of rendering

Pretty-print a ParseError and display the line on which the parse error occurred. The rendered String always ends with a newline.

Note that if you work with include files and have a stack of SourcePoses in ParseError, it's up to you to provide correct input stream corresponding to the file in which parse error actually happened.

parseErrorPretty' is defined in terms of the more general parseErrorPretty_ function which allows to specify tab width as well:

parseErrorPretty' = parseErrorPretty_ defaultTabWidth

Since: 6.0.0

parseErrorPretty_ Source #

Arguments

:: (ShowToken (Token s), LineToken (Token s), ShowErrorComponent e, Stream s)
=> Pos	Tab width
-> s	Original input stream
-> ParseError (Token s) e	Parse error to render
-> String	Result of rendering

Just like parseErrorPretty', but allows to specify tab width.

Since: 6.1.0

sourcePosStackPretty :: NonEmpty SourcePos -> String Source #

Pretty-print a stack of source positions.

Since: 5.0.0

parseErrorTextPretty Source #

Arguments

:: (Ord t, ShowToken t, ShowErrorComponent e)
=> ParseError t e	Parse error to render
-> String	Result of rendering

Pretty-print a 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