Parsec (parser)
Original author(s) | Daan Leijen, Paolo Martini, Antoine Latter |
---|---|
Developer(s) | Herbert Valerio Riedel, Derek Elkins, Antoine Latter, Roman Cheplyaka, Ryan Scott |
Initial release | November 2, 2006[1] |
Stable release | 3.1.17.0
/ April 5, 2024[2] |
Repository | github |
Written in | Haskell |
Operating system | Linux, macOS, Windows |
Platform | Haskell Platform |
Available in | English |
Type | Parser combinator, library |
License | BSD-2-clause |
Website | hackage |
Parsec is a library for writing parsers written in the programming language Haskell.[3] It is based on higher-order parser combinators, so a complicated parser can be made out of many smaller ones.[4] It has been reimplemented in many other languages, including Erlang,[5] Elixir,[6] OCaml,[7] Racket,[8] F#,[9][10] and the imperative programming languages C#,[11] and Java.[12]
Because a parser combinator-based program is generally slower than a parser generator-based program,[citation needed] Parsec is normally used for small domain-specific languages, while Happy is used for compilers such as the Glasgow Haskell Compiler (GHC).[13]
Other Haskell parser combinator libraries that have been derived from Parsec include Megaparsec[14] and Attoparsec.[15]
Parsec is free software released under the BSD-3-Clause license.[16]
Example
[edit]Parsers written in Parsec start with simpler parsers, such as ones that recognize certain strings, and combine them to build a parser with more complicated behavior. For example, digit
parses a digit, and string
parses a specific string (like "hello"
).
Parser combinator libraries like Parsec provide utility functions to run the parsers on real values. A parser to recognize a single digit from a string can be split into two functions: one to create the parser, and a main
function that calls one of these utility functions (parse
in this case) to run the parser:
import Text.Parsec -- has general parsing utility functions
import Text.Parsec.Char -- contains specific basic combinators
type Parser = Stream s m Char => ParsecT s u m String
parser :: Parser
parser = string "hello"
main :: IO ()
main = print (parse parser "<test>" "hello world")
-- prints 'Right "hello"'
We define a Parser
type to make the type signature of parser
easier to read. If we wanted to alter this program, say to read either the string "hello"
or the string "goodbye"
, we could use the operator <|>
, provided by the Alternative
typeclass, to combine two parsers into a single parser that tries either:
parser = string "hello" <|> string "goodbye"
References
[edit]- ^ "parsec 2.0". Hackage. Retrieved 3 September 2019.
- ^ "Releases". Github. Retrieved 22 September 2024.
- ^ "Parsec on Haskell wiki". Haskell Wiki. Retrieved 29 May 2017.
- ^ Leijen, Daan; Meijer, Erik (July 2001). "Parsec: Direct Style Monadic Parser Combinators For The Real World" (PDF). Microsoft Research. Retrieved 22 November 2014.
- ^ "Parsec Erlang". BitBucket. Retrieved 23 November 2014.
- ^ "Nimble Parsec". Github. Retrieved 18 December 2018.
- ^ "Parsec OCaml" (PDF). The OCaml Summer Project. Retrieved 23 November 2014.
- ^ "Megaparsack: Practical Parser Combinators".
- ^ "XParsec by corsis". XParsec. Retrieved 29 May 2017.
- ^ "FParsec". Quanttec. Retrieved 29 May 2017.
- ^ "CSharp monad". Github. Retrieved 10 December 2014.
- ^ "JParsec". Github. Retrieved 14 October 2016.
- ^ "The Glasgow Haskell Compiler (AOSA Vol. 2)". The Architecture of Open Source Applications. Retrieved 23 November 2014.
- ^ "megaparsec: Monadic parser combinators". Hackage. Retrieved 2018-09-10.
- ^ "attoparsec: Fast combinator parsing for bytestrings and text". Hackage. Retrieved 2018-09-10.
- ^ "Parsec". GitHub. 25 October 2021.
External links
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