configurator-pg: Reduced parser for configurator-ng config files

This is a package candidate release! Here you can preview how this package release will appear once published to the main package index (which can be accomplished via the 'maintain' link below). Please note that once a package has been published to the main package index it cannot be undone! Please consult the package uploading documentation for more information.

[maintain] [Publish]

This module provides a simplified and updated interface to the configuration file format of configurator and configurator-ng. Its aim is primarily to allow updating programs that depend on configurator-ng to new versions of GHC without changing the configuration file format.

[Skip to Readme]


Versions,,,,,,, 0.2.0, 0.2.1, 0.2.2, 0.2.3, 0.2.4, 0.2.5, 0.2.5
Change log
Dependencies base (>=4.9 && <4.15), containers (>= && <0.7), megaparsec (>=7.0.0 && <9.1), protolude (>=0.1.10 && <0.4), scientific (>= && <0.4), text (>= && <1.3) [details]
License BSD-3-Clause
Copyright Copyright 2011 MailRank, Inc. Copyright 2011-2014 Bryan O'Sullivan Copyright 2015-2016 Leon P Smith Copyright 2019 Robert Vollmert
Author Robert Vollmert
Category Configuration, Data
Home page
Bug tracker
Uploaded by vollmert at 2020-10-26T10:43:33Z




Maintainer's Corner

For package maintainers and hackage trustees

Readme for configurator-pg-0.2.5

[back to package description]

What is this?

This is a simplified version of the resting configurator-ng, aimed particularly to offer users of configurator-ng such as PostgREST an easy path to migrate to a package that compiles with modern GHC versions and that continues to read existing configuration files.


configurator-pg skips some of configurator-ng's features, and changes the API in other places:


The original configurator-ng is due to MailRank, Inc., Bryan O'Sullivan and Leon P Smith.

The low-level parser (Data.Configurator.Syntax) was initially mostly unchanged, but has since been rewritten with Megaparsec for better error messages. The evaluation (Data.Configurator.Load) is still close to the original. The high-level parser (Data.Configurator.Parser) is original.

File format

In short, the file format supports:

The format is more fully documented in the packages configurator and configurator-ng.

Here's an example:

# listen address
hostname = "localhost"
port = 8000

logdir = "$(HOME)/logs"
logfile = "$(logdir)/log.txt"
loglevels = [1, 4, 5]

users {
  alice = ""
  bob   = ""

# passwords.txt might contain
#   alice = "12345"
#   bob   = "sesame"
passwords {
  import "secrets/passwords.txt"


The following code can be used to parse the example above.

import Data.Configurator

data Settings = Settings
  { hostname  :: Text
  , port      :: Int
  , logfile   :: Maybe FilePath
  , loglevels :: Maybe [Int]
  , users     :: [(Text, Text)]
  , passwords :: [(Text, Text)]

settingsParser :: Parser Config Settings
settingsParser =
    <$> required "hostname" string
    <*> (Maybe.withDefault 1234 <$> optional "port" int)
    <*> optional "logfile" (pack <$> string)
    <*> optional "loglevels" (list int)
    <*> subassocs "users" string
    <*> subassocs "passwords" string

loadSettings :: IO Settings
loadSettings = do
  cfg <- load "settings.cfg"
  case runParser settingsParser cfg of
    Left err       -> die $ "reading config: " <> err
    Right settings -> return settings

Though note that for no apparent reason, subassocs returns the full key, whence the parsed list of users will be

    [ ("users.alice", "")
    , ("users.bob", "")