salak

Configuration (re)loader in Haskell.

salak-yaml

salak-toml

This library define a universal procedure to load configurations and parse properties, also supports reload configuration files.

We can load configurations from command line, environment, configuration files such as yaml or toml etc, and we may want to have our own strategies to load configurations from multi sources and overwrite properties by orders of these sources.

PropConfig defines a common loading strategy:

1. loadCommandLine
2. loadEnvironment
3. loadConfFiles
4. load file from folder salak.conf.dir if defined
5. load file from current folder if enabled
6. load file from home folder if enabled
7. file extension matching, support yaml or toml or any other loader.

Load earlier has higher orders, orders cannot be changed.

ReaderT SourcePack m defines how to read properties:

require "abc.prop"

ReloadableSourcePackT m defines how to read reloadable properties:

requireD "abc.dynamic.prop"

For commandline and environment,

CommandLine:  --package.a.enabled=true
Environment: PACKAGE_A_ENABLED: false

Usage:

Environment:

export TEST_CONFIG_NAME=daniel

Current Directory: salak.yaml

test.config:
  name: noop
  dir: ls

Current Directory: salak.toml

[test.config]
ext=2

data Config = Config
  { name :: Text
  , dir  :: Maybe Text
  , ext  :: Int
  } deriving (Eq, Show)

instance MonadCatch m => FromProp m Config where
  fromProp = Config
    <$> "user" ? pattern "[a-z]{5,16}"
    <*> "pwd"
    <*> "ext" .?= 1

main = runSalakWith "salak" (YAML :|: TOML) $ do
  c :: Config <- require "test.config"
  lift $ print c=

GHCi play

λ> :set -XFlexibleInstances -XMultiParamTypeClasses 
λ> import Salak
λ> import Data.Default
λ> import Data.Text(Text)
λ> data Config = Config { name :: Text, dir  :: Maybe Text, ext  :: Int} deriving (Eq, Show)
λ> instance MonadCatch m => FromProp m Config where fromProp = Config <$> "user" <*> "dir" <*> "ext" .?= 1
λ> runSalak def (require "") :: IO Config
Config {name = "daniel", dir = Nothing, ext = 1}

TODO:

• Recover placeholder
• Add git pull support.
• Add automatic reloading.