Documentation

The in-memory configuration data.

Information about the default configuration. Contains all the settings (that you declare using getDefaultConfig) and their default values. It is useful when you save a configuration file, if you give this information to saveSettings, it will save default options in the configuration file in a commented form, as a form of documentation to a user who would edit the configuration file. However this is completely optional, you can give emptyDefaultConfig if you don't want this behaviour.

The type of a setting. It contains the setting name (key in the configuration file) and its default value.

It is advised to have a module in your project handling settings. In this module, you'd have all the settings declared at the toplevel, and exported. The rest of the application can then do

getSetting <setting>
setSetting <conf> <setting> <value>

and so on.

Setting declares a simple setting. A value for that setting will be stored in the configuration file in a single line.

ListSetting however declares a list setting. While it is perfectly fine to store lists using the usual Setting constructor, if you have a list of more complex items, you will get very long lines and a configuration file very difficult to edit or review by hand.

The ListSetting will store settings using one line per item in the list:

testList :: Setting [String]
testList = ListSetting "testList" ["list1", "list2", "list3"]

Now the configuration file looks like that:

testList_1="list1"
testList_2="list2"
testList_3="list3"

Also note that an empty ListSetting is stored like so:

testList=

see the getDefaultConfig documentation.

Used in combination with setting to register settings. Registering settings is optional, see DefaultConfig.

defaultSettings :: DefaultConfig
defaultSettings = getDefaultConfig $ do
    setting <setting1>
    setting <setting2>

Default configuration containing no options. It's fine to give that to saveSettings if you don't want default settings being written to the configuration file in commented form (see DefaultConfig)

Where to look for or store the configuration file.

Read settings from disk. Because it is doing file I/O it is smart to wrap the call with a try, as I/O exceptions can be thrown. Also, the function will throw a ParseException if the file is not properly formatted. NOTE that if the file is properly formatted in general, but a value is stored in an invalid format (for instance "hello" for a Double), you will get no error and get the default value for that setting when you attempt to read it.

This function returns a pair. The first element is the configuration itself, which you can use to save back or modify the configuration. The second element is a function wrapped in the GetSetting newtype. This function allows you to read a configuration option simply by giving that option (without that callback you'd have to call getSetting settings <setting>, so the callback lets you save a parameter). There is no such shortcut for setSetting though, as it's normally used less often and in other contexts, it is probably OK to have that extra parameter for the setSetting.

Example of use:

readResult <- try $ readSettings (Path "my.config")
case readResult of
 Right (conf, GetSetting getSetting) -> do
     let textSize = getSetting fontSize
     saveSettings emptyDefaultConfig (Path "my.config") conf
 Left (x :: SomeException) -> error "Error reading the config file!"

The configuration file is in an invalid format.

It is advised to run the save within a try call because it does disk I/O, otherwise the call is straightforward.

Change the value of a setting. You'll have to call saveSettings so that the change is written to disk.

Most of the time you can use the second function you get from readSettings, wrapped in a GetSetting newtype, however sometimes it's nicer to just pass a single Conf to other functions if you're going to read or write to the configuration. The GetSetting lets you only read.