panfiguration: Merge environment variables and command line options generically

Usage

Panfiguration is a library that provides a composable, automatically-derived interface for configuration parameters.

Currently three backends are supported; envs for environment variables, opts for command-line options and defaults for default values. The Monoid instance makes these backends composable. See the example below for the basic usage.

Example

import Barbies.TH
import Panfiguration

passthroughBareB [d|
    data ServerArgs = ServerArgs
        { http_host :: String
        , http_port :: Int
        , enable_service_log :: Bool
        , environment :: String
        }
    |]

getServerArgs :: IO ServerArgs
getServerArgs = run $ mconcat
    [ logger putStrLn
    , declCase snake
    , envs `withNames` \names -> names
        { http_host = "HTTP_HOST"
        , http_port = "HTTP_PORT"
        }
    , opts `asCase` kebab
    , defaults ServerArgs
        { http_host = Just "0.0.0.0"
        , http_port = Just 8080
        , enable_service_log = Just True
        , environment = Nothing -- required parameter
        }
    ]

Naming conventions

declCase specifies the naming convention of the Haskell data declaration (the default is camel). The naming conventions are configurable by the asCase modifier. By default, envs and opts uses SNAKE_CASE and kebab-case respectively.

The following styles are supported:

AsIs
Camel
camel
snake
SNAKE
kebab
KEBAB
Prefixed <str>

You can also override individual names directly by withNames.