polyparse-1.12: A variety of alternative parser combinator libraries.

Text.ParserCombinators.Poly.Lex

Description

In a strict language, where creating the entire input list of tokens in one shot may be infeasible, we can use a lazy "callback" kind of architecture instead. The lexer returns a single token at a time, together with a continuation.

This module defines a Parser type (capable of use with the Poly combinators), specialised to the callback-lexer style of input stream.

Synopsis

# The Parser datatype

data LexReturn t #

In a strict language, where creating the entire input list of tokens in one shot may be infeasible, we can use a lazy "callback" kind of architecture instead. The lexer returns a single token at a time, together with a continuation. The next parser is responsible for pulling on the token stream, applying the continuation where necessary.

Constructors

 LexReturn t String (String -> LexReturn t) LexFinish

newtype Parser t a #

This Parser datatype is a specialised parsing monad with error reporting. This version is specialised to pre-lexed String input, where the lexer has been written to yield a LexReturn.

Constructors

 P (LexReturn t -> Result (LexReturn t) a)

Instances

 Monad (Parser t) # Methods(>>=) :: Parser t a -> (a -> Parser t b) -> Parser t b #(>>) :: Parser t a -> Parser t b -> Parser t b #return :: a -> Parser t a #fail :: String -> Parser t a # # Methodsfmap :: (a -> b) -> Parser t a -> Parser t b #(<$) :: a -> Parser t b -> Parser t a # # Methodspure :: a -> Parser t a #(<*>) :: Parser t (a -> b) -> Parser t a -> Parser t b #(*>) :: Parser t a -> Parser t b -> Parser t b #(<*) :: Parser t a -> Parser t b -> Parser t a # # Methodsempty :: Parser t a #(<|>) :: Parser t a -> Parser t a -> Parser t a #some :: Parser t a -> Parser t [a] #many :: Parser t a -> Parser t [a] # # # Methodscommit :: Parser t a -> Parser t a #adjustErr :: Parser t a -> (String -> String) -> Parser t a #oneOf' :: [(String, Parser t a)] -> Parser t a # data Result z a # A return type like Either, that distinguishes not only between right and wrong answers, but also has commitment, so that a failure cannot be undone. This should only be used for writing very primitive parsers - really it is an internal detail of the library. The z type is the remaining unconsumed input. Constructors  Success z a Failure z String Committed (Result z a) Instances  # Methodsfmap :: (a -> b) -> Result z a -> Result z b #(<$) :: a -> Result z b -> Result z a #

runParser :: Parser t a -> LexReturn t -> (Either String a, String) #

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.

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.