Hints represent a collection of ErrorItems to be included into ParseError (when it's a TrivialError) as “expected” message items when a parser fails without consuming input right after successful parser that produced the hints.

For example, without hints you could get:

>>> parseTest (many (char 'r') <* eof) "ra"
1:2:
unexpected 'a'
expecting end of input

We're getting better error messages with the help of hints:

>>> parseTest (many (char 'r') <* eof) "ra"
1:2:
unexpected 'a'
expecting 'r' or end of input

All information available after parsing. This includes consumption of input, success (with the returned value) or failure (with the parse error), and parser state at the end of parsing.

See also: Consumption, Result.

Whether the input has been consumed or not.

See also: Result, Reply.

Whether the parser has failed or not. On success we include the resulting value, on failure we include a ParseError.

See also: Consumption, Reply.

ParsecT e s m a is a parser with custom data component of error e, stream type s, underlying monad m and return type a.

Convert a ParseError record into Hints.

withHints hs c makes “error” continuation c use given hints hs.

Note that if resulting continuation gets ParseError that has custom data in it, hints are ignored.

accHints hs c results in “OK” continuation that will add given hints hs to third argument of original continuation c.

Replace the most recent group of hints (if any) with the given ErrorItem (or delete it if Nothing is given). This is used in the label primitive.

Low-level unpacking of the ParsecT type.

Transform any custom errors thrown by the parser using the given function. Similar in function and purpose to withExceptT.

Note that the inner parser will start with an empty collection of “delayed” ParseErrors. Any delayed ParseErrors produced in the inner parser will be lifted by applying the provided function and added to the collection of delayed parse errors of the outer parser.

Since: 7.0.0