License	BSD-3-Clause
Maintainer	Jamie Willis, Gigaparsec Maintainers
Stability	experimental
Safe Haskell	Safe
Language	Haskell2010

Text.Gigaparsec.Errors.ErrorGen

Contents

Documentation
- Error Generators
  - Blank Generators
- Error Generating Combinators

Description

This module can be used to generate hand-tuned error messages without using monadic bind.

Synopsis

data ErrorGen a
- = SpecializedGen {
  - messages :: a -> [String]
  - adjustWidth :: a -> Word -> Word
  }
- | VanillaGen {
  - unexpected :: a -> UnexpectedItem
  - reason :: a -> Maybe String
  - adjustWidth :: a -> Word -> Word
  }
data UnexpectedItem
- = RawItem
- | EmptyItem
- | NamedItem String
vanillaGen :: ErrorGen a
specializedGen :: ErrorGen a
asFail :: ErrorGen a -> Parsec (a, Word) -> Parsec b
asSelect :: ErrorGen a -> Parsec (Either (a, Word) b) -> Parsec b
asErr :: ErrorGen a -> a -> Word -> Parsec b

Documentation

Error Generators

data ErrorGen a Source #

This type describes special primitives that can use the results of a previous parser to form and raise an error message. This is not something that is normally possible with raw combinators, without using (>>=), which is expensive.

Primarily, these are designed to be used with filterSWith/verifiedWith/preventWith but can be used in other parsers as well.

Constructors

SpecializedGen	An error generator for Specialized errors, which can tune the freeform messages of the error.
Fields messages :: a -> [String] Produces the messages of the error message when given the result of the offending parser. adjustWidth :: a -> Word -> Word Controls how wide an error is based on the value `a` and width `Word` provided.
VanillaGen	An error generator for Vanilla errors, which can tune the unexpected message and a generated reason.
Fields unexpected :: a -> UnexpectedItem Produces the unexpected component (if any) of the error message when given the result of the offending parser. reason :: a -> Maybe String Produces the reason component (if any) of the error message when given the result of the offending parser. adjustWidth :: a -> Word -> Word Controls how wide an error is based on the value `a` and width `Word` provided.

data UnexpectedItem Source #

This type describes how to form the unexpected component of a vanilla error message from a VanillaGen.

This includes the different sorts of 'unexpected item' messages that may occur; whether to display the expected characters, a name for the expected expression, or not to display at all.

Constructors

RawItem	The error should use whatever input was consumed by the offending parser, verbatim.
EmptyItem	The error should not have an unexpected component at all (as in `filterS`).
NamedItem String	The error should use the given name as the unexpected component.

Blank Generators

vanillaGen :: ErrorGen a Source #

A blank Vanilla error generator, which does not affect the unexpected message or reason.

specializedGen :: ErrorGen a Source #

The default Specialized error generator, which does not affect the error message.

Error Generating Combinators

These combinators create parsers that fail or raise errors with messages desribed by a given ErrorGen.

asFail Source #

Arguments

:: ErrorGen a	`errGen`, the generator for the error message.
-> Parsec (a, Word)	`p`, a parser that returns a result `x` and its width `w`.
-> Parsec b	A parser that unconditionally fails with a message described by `errGen`, using the result of `p`.

This combinator takes a given parser p and unconditionally fails with a message based on p's results.

asSelect Source #

Arguments

:: ErrorGen a	`errGen`, the generator for the error message.
-> Parsec (Either (a, Word) b)	`p`, a parser which may produce a bad result of type `a`
-> Parsec b	A parser that fails if `p` produces a bad result, otherwise returns the result of `p` if it is a `b`

This combinator takes a given parser p and, if p returns an a, fails with a message based on this result.

asErr Source #

Arguments

:: ErrorGen a	`errGen`, the generator for the error message to raise.
-> a	`x`, the result of the offending parser
-> Word	The width of the parsed result, `x`.
-> Parsec b	A parser that unconditionally raises an error described by `errGen`.

Given a parser result and its width, raise an error according to the given error generator.