- newtype Parser t a = P (Parser t a)
- data Result z a
- runParser :: Parser t a -> [t] -> (a, [t])
- next :: Parser t t
- eof :: Parser t ()
- satisfy :: (t -> Bool) -> Parser t t
- onFail :: Parser t a -> Parser t a -> Parser t a
- reparse :: [t] -> Parser t ()
- module Text.ParserCombinators.Poly.Base
- module Control.Applicative
The Parser datatype
The only differences between a Plain and a Lazy parser are the instance of Applicative, and the type (and implementation) of runParser. We therefore need to newtype the original Parser type, to allow it to have a different instance.
A return type like Either, that distinguishes not only between right and wrong answers, but also has commitment, so that a failure cannot be undone. This should only be used for writing very primitive parsers - really it is an internal detail of the library. The z type is the remaining unconsumed input.
Return the next token if it satisfies the given predicate.
p means parse p, unless p fails, in which case
parse q instead.
Can be chained together to give multiple attempts to parse something.
(Note that q could itself be a failing parser, e.g. to change the error
message from that defined in p to something different.)
However, a severe failure in p cannot be ignored.
Push some tokens back onto the front of the input stream and reparse. This is useful e.g. for recursively expanding macros. When the user-parser recognises a macro use, it can lookup the macro expansion from the parse state, lex it, and then stuff the lexed expansion back down into the parser.
Re-export all more general combinators