A parser combinator library.
See the Haddock documentation for information about the various parsers.
The following program defines a parser (expr1) that parses arithmetic
expressions, such as 1 + 2 * 3^4 / 3 - 5, and evaluates them to an Int.
import Comb
expr1 =
chainl expr2
( (+) <$ symbol '+'
<|> (-) <$ symbol '-')
expr2 =
chainl expr3
( (*) <$ symbol '*'
<|> div <$ symbol '/')
expr3 = chainr expr4 ((^) <$ symbol '^')
expr4 = many space *> (parenthesised expr1 <|> int) <* many space
result1 = runParser expr1 "9 + 5 * 3^2" :: Maybe (Int, String)
-- >>> Just (54, "")To keep track of the current position in the file, you can use WithPosition:
result2 = runParser expr1 (Positioned positionBegin "9 + 5 * 3^2") :: Maybe (Int, Positioned String)
-- >>> Just (54, Positioned { position = Position { line = 1, column = 12, file = Nothing }, stream = "" })When using a Functor different from Maybe, Positioned can be used to
create better error messages.
To improve error handling, empty (of Alternative) could be replaced by more
specialised error values. For example:
class Applicative f => ParserAlternative f where
eof :: f a -- error value when the end of file is reached
-- some function when there is no character match
-- etc.Copyright (C) 2019 Splinter Suidman
This program is free software: you can redistribute it and/or modify it under the terms of the GNU Affero General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Affero General Public License for more details.
A copy of the GNU Affero General Public License is included in the file LICENSE.