Moduleyaml-0.11.11.2Haskell2010

Data.Yaml.Config

Functionality for using YAML as configuration files

In particular, merging environment variables with yaml values

loadYamlSettings is a high-level API for loading YAML and merging environment variables. A yaml value of _env:ENV_VAR:default will lookup the environment variable ENV_VAR.

On a historical note, this code was taken directly from the yesod web framework's configuration module.

1 type
10 values

Packageyaml-0.11.11.2
Exports11
LanguageHaskell2010
LicenceBSD-3-Clause
SourceConfig.hs

High-level

2 declarations

valueloadYamlSettings

:: FromJSON settings
=> [FilePath]
run time config files to use, earlier files have precedence
-> [Value]
any other values to use, usually from compile time config. overridden by files
-> EnvUsage
-> IO settings

Load the settings from the following three sources:

Run time config files
Run time environment variables
The default compile time config file

For example, to load up settings from config/foo.yaml and allow overriding from the actual environment, you can use:

loadYamlSettings ["config/foo.yaml"] [] useEnv

valueloadYamlSettingsArgs

:: FromJSON settings
=> [Value]
any other values to use, usually from compile time config. overridden by files
-> EnvUsage
use environment variables
-> IO settings

Same as loadYamlSettings, but get the list of runtime config files from the command line arguments.

EnvUsage

datadata EnvUsage

Defines how we want to use the environment variables when loading a config file. Use the smart constructors provided by this module.

valueignoreEnv :: EnvUsage

Do not use any environment variables, instead relying on defaults values in the config file.

valueuseEnv :: EnvUsage

Use environment variables when available, otherwise use defaults.

valuerequireEnv :: EnvUsage

Do not use default values from the config file, but instead take all overrides from the environment. If a value is missing, loading the file will throw an exception.

valueuseCustomEnv :: KeyMap Text -> EnvUsage

Same as useEnv, but instead of the actual environment, use the provided HashMap as the environment.

valuerequireCustomEnv :: KeyMap Text -> EnvUsage

Same as requireEnv, but instead of the actual environment, use the provided HashMap as the environment.

Lower level

3 declarations

valueapplyCurrentEnv

:: Bool
require an environment variable to be present?
-> Value
-> IO Value

A convenience wrapper around applyEnvValue and getCurrentEnv

valuegetCurrentEnv :: IO (KeyMap Text)

Get the actual environment as a HashMap from Text to Text.

valueapplyEnvValue

:: Bool
require an environment variable to be present?
-> KeyMap Text
-> Value
-> Value

Override environment variable placeholders in the given Value with values from the environment.

If the first argument is True, then all placeholders _must_ be provided by the actual environment. Otherwise, default values from the Value will be used.