Data.Yaml.Config

Library for read config files in YAML format.

example.yaml:

server:
    port: 8080
    logs:
        access: /var/log/server/access.log
        error:  /var/log/server/error.log

Usage example:

module Main where
import Prelude hiding (lookup)
import Data.Word (Word16)
import Data.Yaml.Config (load, subconfig, lookupDefault, lookup)

main :: IO ()
main = do
    config <- load "./example.yaml"

    serverConfig <- subconfig "server" config
    let interface = lookupDefault "interface" "127.0.0.1" serverConfig
        port :: Word16 = lookupDefault "port" 80 serverConfig

    logConfig <- subconfig "logs" serverConfig
    accessLog <- lookup "access" logConfig
    errorLog <- lookup "error" logConfig

    mapM_ putStrLn [interface, (show port), errorLog, accessLog]

Documentation

data Config

Type contains config section and path from root.

Instances

Eq Config

Show Config

NFData Config

type Key = Text

Config or field name

newtype KeyError

This error can be raised if config has not target path.

Constructors

KeyError Key

Instances

Show KeyError

Exception KeyError

load :: FilePath -> IO Config

Attempts to load a config from a given YAML file. Fails with InvalidYaml if the file does not exist.

>>> config <- load "example.yaml"

keys :: Config -> [Key]

Returns all toplevel keys in a config.

>>> keys config
["section1","section2"]

subconfig

Arguments

:: Monad m

=> Key

Subconfig name

-> Config

(Sub)Config to narrow into

-> m Config

Subconfig

Narrows into a config section corresponding to a given key. Fails with a KeyError if a key doesn't exist at the current level.

>>> :set -XOverloadedStrings
>>> sub <- subconfig "section1" config

lookup

Arguments

:: (Monad m, FromJSON a)

=> Key

Field name

-> Config

Config to query

-> m a

Looked up value

Returns a value for a given key. Fails with a KeyError if the key doesn't exist.

>>> keys sub
["field1","field2"]
>>> putStrLn =<< lookup "field1" sub
value1

lookupDefault

Arguments

:: FromJSON a

=> Key

Field name

-> a

Default value

-> Config

Config to query

-> a

Looked up or default value

Returns a value for a given key or a default value if a key doesn't exist.

>>> lookupDefault "field3" "def" sub
"def"