Text.ParserCombinators.Poly.Plain

The Parser datatype

newtype Parser t a

This Parser datatype is a fairly generic parsing monad with error reporting. It can be used for arbitrary token types, not just String input. (If you require a running state, use module Poly.State instead)

Constructors

P ([t] -> Result [t] a)

Instances

Alternative (Parser t)

Monad (Parser t)

Functor (Parser t)

Applicative (Parser t)

PolyParse (Parser t)

Commitment (Parser t)

data Result z a

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.

Constructors

Success z a

Failure z String

Committed (Result z a)

Instances

Functor (Result z)

runParser :: Parser t a -> [t] -> (Either String a, [t])

Apply a parser to an input token sequence.

Basic parsers

next :: Parser t t

Simply return the next token in the input tokenstream.

eof :: Parser t ()

Succeed if the end of file/input has been reached, fail otherwise.

satisfy :: (t -> Bool) -> Parser t t

Return the next token if it satisfies the given predicate.

satisfyMsg :: Show t => (t -> Bool) -> String -> Parser t t

Return the next token if it satisfies the given predicate. The String argument describes the function, for better error messages.

onFail :: Parser t a -> Parser t a -> Parser t a infixl 6

p onFail q 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.

Re-parsing

reparse :: [t] -> Parser t ()

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

module Text.ParserCombinators.Poly.Base

module Control.Applicative