parsec-3.1.3: Monadic parser combinators

Safe HaskellSafe-Inferred



Parse errors



data Message Source

This abstract data type represents parse error messages. There are four kinds of messages:

  data Message = SysUnExpect String
               | UnExpect String
               | Expect String
               | Message String

The fine distinction between different kinds of parse errors allows the system to generate quite good error messages for the user. It also allows error messages that are formatted in different languages. Each kind of message is generated by different combinators:

  • A SysUnExpect message is automatically generated by the satisfy combinator. The argument is the unexpected input.
  • A UnExpect message is generated by the unexpected combinator. The argument describes the unexpected item.
  • A Expect message is generated by the <?> combinator. The argument describes the expected item.
  • A Message message is generated by the fail combinator. The argument is some general parser message.


SysUnExpect !String 
UnExpect !String 
Expect !String 
Message !String 


Enum Message 
Eq Message 
Ord Message 

messageString :: Message -> StringSource

Extract the message string from an error message

data ParseError Source

The abstract data type ParseError represents parse errors. It provides the source position (SourcePos) of the error and a list of error messages (Message). A ParseError can be returned by the function parse. ParseError is an instance of the Show class.


Show ParseError 

errorPos :: ParseError -> SourcePosSource

Extracts the source position from the parse error

errorMessages :: ParseError -> [Message]Source

Extracts the list of error messages from the parse error

showErrorMessages :: String -> String -> String -> String -> String -> [Message] -> StringSource