sexp-grammar: Invertible grammar combinators for S-expressions

[ bsd3, language, library ] [ Propose Tags ]

Serialisation to and deserialisation from S-expressions derived from a single grammar definition.


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Versions 1.0.0, 1.1.0, 1.1.1, 1.2.0, 1.2.0.1, 1.2.1, 1.2.2, 1.2.3, 1.2.4, 1.3.0, 2.0.0, 2.0.1 (info)
Dependencies array (==0.5.*), base (>=4.7 && <5.0), bytestring (==0.10.*), containers (>=0.5.5 && <0.6), deepseq (>=1.0 && <2.0), invertible-grammar (==0.1.*), prettyprinter (>=1 && <1.3), recursion-schemes (>=5.0 && <6.0), scientific (>=0.3.3 && <0.4), semigroups (>=0.16 && <0.19), text (==1.2.*), utf8-string (>=1.0 && <2.0) [details]
License BSD-3-Clause
Author Eugene Smolanka, Sergey Vinokurov
Maintainer Eugene Smolanka <esmolanka@gmail.com>, Sergey Vinokurov <serg.foo@gmail.com>
Category Language
Home page https://github.com/esmolanka/sexp-grammar
Source repo head: git clone https://github.com/esmolanka/sexp-grammar
Uploaded by EugeneSmolanka at Wed Jun 13 01:22:26 UTC 2018
Distributions LTSHaskell:2.0.1, NixOS:2.0.1, Stackage:2.0.1
Downloads 1728 total (139 in the last 30 days)
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Readme for sexp-grammar-2.0.1

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sexp-grammar

It is a library of invertible parsing combinators for S-expressions. The combinators -- primitive grammars -- not only encode a way how to parse S-expressions into a Haskell value, but how to serialise it back into an S-expression.

The approach used in sexp-grammar is inspired by the paper Invertible syntax descriptions: Unifying parsing and pretty printing and a similar implementation of invertible grammar approach for JSON, library by Martijn van Steenbergen called JsonGrammar2.

Let's have a look at sexp-grammar at work:

{-# LANGUAGE DeriveGeneric     #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE TypeOperators     #-}

import GHC.Generics
import Data.Text (Text)
import Language.SexpGrammar
import Language.SexpGrammar.Generic

data Person = Person
  { pName    :: Text
  , pAddress :: Text
  , pAge     :: Maybe Int
  } deriving (Show, Generic)

instance SexpIso Person where
  sexpIso = with $ \person ->  -- Person is isomorphic to:
    list (                           -- a list with
      el (sym "person") >>>          -- a symbol "person",
      el string         >>>          -- a string, and
      props (                        -- a property-list with
        "address" .:  string >>>     -- a keyword :address and a string value, and
        "age"     .:? int))  >>>     -- an optional keyword :age with int value.
    person

We've just defined an isomorphism between S-expression representation and Haskell data record representation of the same information.

ghci> :set -XTypeApplications
ghci> import Language.SexpGrammar
ghci> import Data.ByteString.Lazy.Char8 (pack, unpack)
ghci> person <- either error return . decode @Person . pack =<< getLine
(person "John Doe" :address "42 Whatever str." :age 25)
ghci> person
Person {pName = "John Doe", pAddress = "42 Whatever str.", pAge = Just 25}
ghci> putStrLn (either id unpack (encode person))
(person "John Doe" :address "42 Whatever str." :age 25)

See more examples in the repository.