config-schema: Schema definitions for the config-value package

[ language, library ] [ Propose Tags ]

This package makes it possible to define schemas for use when loading configuration files using the config-value format. These schemas can be used to process a configuration file into a Haskell value or to automatically generate documentation for the file format.

[Skip to Readme]
Versions [RSS] [faq],,,,,,,,,,,,,
Change log
Dependencies base (>=4.9 && <4.17), config-value (==0.8.*), containers (>=0.5 && <0.7), free (>=4.12 && <5.2), kan-extensions (>=5.0.2 && <5.3), pretty (>=1.1.2 && <1.2), semigroupoids (>=5.1 && <5.4), text (==1.2.*), transformers (>=0.4 && <0.6) [details]
License ISC
Copyright Eric Mertens 2017
Author Eric Mertens
Revised Revision 2 made by EricMertens at 2021-11-16T18:31:52Z
Category Language
Home page
Bug tracker
Source repo head: git clone
Uploaded by EricMertens at 2021-03-11T19:32:16Z
Distributions Debian:, NixOS:
Downloads 8900 total (71 in the last 30 days)
Rating 2.0 (votes: 1) [estimated by Bayesian average]
Your Rating
  • λ
  • λ
  • λ
Status Hackage Matrix CI
Docs available [build log]
Last success reported on 2021-03-11 [all 1 reports]


[Index] [Quick Jump]


Note: This package has metadata revisions in the cabal description newer than included in the tarball. To unpack the package including the revisions, use 'cabal get'.

Maintainer's Corner

For package maintainers and hackage trustees


Readme for config-schema-

[back to package description]


Hackage Build Status

Live Demo

The config-value and config-schema packages are available in a live demo.


This package allows the user to define configuration schemas suitable for matching against configuration files written in the config-value format. These schemas allow the user to extract an arbitrary Haskell value from an interpretation of a configuration file. It also allows the user to programatically generate documentation for the configuration files accepted by the loader.

{-# Language OverloadedStrings, ApplicativeDo #-}
module Example where

import qualified Data.Text as Text
import           Data.Text (Text)
import           Data.Monoid ((<>))
import           Data.Functor.Alt ((<!>))
import           Data.List.NonEmpty (NonEmpty)

import           Config
import           Config.Schema

exampleFile :: Text
exampleFile =
  " name: \"Johny Appleseed\" \n\
  \ age : 99                  \n\
  \ happy: yes                \n\
  \ kids:                     \n\
  \   * name: \"Bob\"         \n\
  \   * name: \"Tom\"         \n"

exampleValue :: Value Position
Right exampleValue = parse exampleFile

exampleSpec :: ValueSpec Text
exampleSpec = sectionsSpec "" $
  do name  <- reqSection  "name" "Full name"
     age   <- reqSection  "age"  "Age of user"
     happy <- optSection' "happy" yesOrNo
              "Current happiness status"
     kids  <- reqSection' "kids"  (oneOrList kidSpec)
              "All children's names"

     return $
       let happyText = case happy of Just True  -> " and is happy"
                                     Just False -> " and is not happy"
                                     Nothing    -> " and is private"

       in name <> " is " <> Text.pack (show (age::Integer)) <>
             " years old and has kids " <>
             Text.intercalate ", " kids <>

kidSpec :: ValueSpec Text
kidSpec = sectionsSpec "kid" (reqSection "name" "Kid's name")

-- | Matches the 'yes' and 'no' atoms
yesOrNo :: ValueSpec Bool
yesOrNo = True  <$ atomSpec "yes" <!>
          False <$ atomSpec "no"

printDoc :: IO ()
printDoc = print (generateDocs exampleSpec)
-- *Example> printDoc
-- Top-level configuration file fields:
--     name: REQUIRED text
--        Full name
--     age: REQUIRED integer
--        Age of user
--     happy: `yes` or `no`
--        Current happiness status
--     kids: REQUIRED kid or list of kid
--        All children
-- kid
--     name: REQUIRED text
--        Kid's name

example :: Either (NonEmpty (LoadError Position)) Text
example = loadValue exampleSpec exampleValue
-- *Example> exampleVal
-- Right "Johny Appleseed is 99 years old and has kids Bob, Tom and is happy"