envparse: Parse environment variables

[ bsd3, library, system ] [ Propose Tags ]

Here's a simple example of a program that uses envparse's parser:

module Main (main) where

import Control.Monad (unless)
import Env

data Hello = Hello { name :: String, quiet :: Bool }

hello :: IO Hello
hello = Env.parse (header "envparse example") $
  Hello <$> var (str <=< nonempty) "NAME"  (help "Target for the greeting")
        <*> switch                 "QUIET" (help "Whether to actually print the greeting")
main :: IO ()
main = do
  Hello {name, quiet} <- hello
  unless quiet $
    putStrLn ("Hello, " ++ name ++ "!")

The NAME environment variable is mandatory and contains the name of the person to greet. QUIET, on the other hand, is an optional boolean flag, false by default, that decides whether the greeting should be silent.

If the NAME variable is undefined in the environment then running the program will result in the following help text:

envparse example
Available environment variables:
  NAME                   Target for the greeting
  QUIET                  Whether to actually print the
Parsing errors:
  NAME is unset

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Versions [RSS] 0.1.0, 0.2.0, 0.2.1, 0.2.2, 0.3.0, 0.3.1, 0.3.2, 0.3.3, 0.4, 0.4.1, 0.5.0
Change log CHANGELOG.markdown
Dependencies base (>=4.6 && <5), containers [details]
License BSD-3-Clause
Copyright 2015 Matvey Aksenov
Author Matvey Aksenov
Maintainer matvey.aksenov@gmail.com
Category System
Home page https://supki.github.io/envparse
Source repo head: git clone https://github.com/supki/envparse
this: git clone https://github.com/supki/envparse(tag 0.5.0)
Uploaded by MatveyAksenov at 2022-06-13T16:42:13Z
Distributions LTSHaskell:0.5.0, NixOS:0.5.0, Stackage:0.5.0
Reverse Dependencies 13 direct, 27 indirect [details]
Downloads 8876 total (55 in the last 30 days)
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Status Docs available [build log]
Last success reported on 2022-06-13 [all 1 reports]

Readme for envparse-0.5.0

[back to package description]


optparse-applicative, but for environment variables

See example/Main.hs for an executable example

As to why anyone would want to use environment to configure their applications, here's what some folks think about it.