GHC 9.14.1 · lts/ghc-9.14.x · 6d5fdfd · 2026-10-12
Moduleyaml-0.11.11.2Haskell2010
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.
loadYamlSettings 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"] [] useEnvloadYamlSettingsArgs Same as loadYamlSettings, but get the list of runtime config files from
the command line arguments.
Defines how we want to use the environment variables when loading a config file. Use the smart constructors provided by this module.
Do not use any environment variables, instead relying on defaults values in the config file.
Use environment variables when available, otherwise use defaults.
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.
Same as useEnv, but instead of the actual environment, use the provided
HashMap as the environment.
Same as requireEnv, but instead of the actual environment, use the
provided HashMap as the environment.
applyCurrentEnv A convenience wrapper around applyEnvValue and getCurrentEnv
Get the actual environment as a HashMap from Text to Text.
applyEnvValue 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.