This module contains the definitions for a generic parser, with running state. These are the parts that are shared between the State and StateLazy variations. Do not import this module directly, but only via T.P.Poly.State or T.P.Poly.StateLazy.
- newtype Parser s t a = P (s -> [t] -> Result ([t], s) a)
- data Result z a
- next :: Parser s t t
- eof :: Parser s t ()
- satisfy :: (t -> Bool) -> Parser s t t
- onFail :: Parser s t a -> Parser s t a -> Parser s t a
- stUpdate :: (s -> s) -> Parser s t ()
- stQuery :: (s -> a) -> Parser s t a
- stGet :: Parser s t s
- reparse :: [t] -> Parser s t ()
The Parser datatype
Parser datatype is a fairly generic parsing monad with error
reporting, and running state.
It can be used for arbitrary token types, not just String input.
(If you do not require a running state, use module Poly.Plain instead)
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.