The config-schema package

[Tags:library, test]

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

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Change log
Dependencies base (>=4.8 && <4.11), config-value (==0.6.*), containers (==0.5.*), free (==4.12.*), kan-extensions (>=5.0.2 && <5.1), pretty (>=1.1.2 && <1.2), semigroupoids (>=5.1 && <5.3), semigroups (==0.18.*), text (==1.2.*), transformers (>=0.4 && <0.6) [details]
License ISC
Copyright Eric Mertens 2017
Author Eric Mertens
Category Language
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Source repository head: git clone
Uploaded Fri Jun 2 15:21:15 UTC 2017 by EricMertens
Distributions NixOS:
Downloads 327 total (108 in the last 30 days)
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Status Docs uploaded by user
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Readme for config-schema-


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

-- | Matches the 'yes' and 'no' atoms
yesOrNo :: ValueSpecs 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"