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.
- data LexReturn t
- newtype Parser t a = P (LexReturn t -> Result (LexReturn t) a)
- data Result z a
- runParser :: Parser t a -> LexReturn t -> (Either String a, String)
- 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
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.
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
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.
Apply a parser to an input token sequence.
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