salak
Configuration (re)loader in Haskell.
salak-yaml
salak-toml
Introduction
This library defines a universal procedure to load configurations and parse properties, also supports reload configuration files.
Parse Functions
MonadSalak
monad provide a unified function require
to parse properties. Here are some examples.
a :: Bool <- require "bool.key"
b :: Maybe Int <- require "int.optional.key"
c :: Either String Int <- require "int.error.key"
d :: IO Int <- require "int.reloadable.key" -- This property can be changed by reloading configurations.
Load Strategy
We can load configurations from command lines, environment, configuration files such as yaml or toml etc., and we may want to have our own strategies to load configurations from multiply sources and overwrite properties by orders of these sources.
PropConfig
defines a common loading strategy:
- loadCommandLine
- loadEnvironment
- loadConfFiles
- load file from folder
application.dir
if defined
- load file from current folder if enabled
- load file from home folder if enabled
- file extension matching, support yaml or toml or any other loader.
Load earlier has higher priorities. Priorities cannot be changed.
For command lines 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 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 -XOverloadedStrings
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 FromProp m Config where fromProp = Config <$> "user" <*> "dir" <*> "ext" .?= 1
λ> runSalak def (require "") :: IO Config
Config {name = "daniel", dir = Nothing, ext = 1}
TODO:
- Add git pull support.
- Add automatic reloading.