A library to deal with application settings.
This library deals with read-write application settings.
You will have to specify the settings that your application
uses, their name, types and default values.
Setting types must implement the Read and Show typeclasses.
The settings are saved in a file in an INI-like key-value format
(without sections).
Reading and updating settings is done in pure code, the IO
monad is only used to load settings and save them to disk.
It is advised for the user to create a module in your project
holding settings handling.
You can then declare settings:
fontSize :: Setting Double
fontSize = Setting "fontSize" 14
dateFormat :: Setting String
dateFormat = Setting "dateFormat" "%x"
backgroundColor :: Setting (Int, Int, Int)
backgroundColor = Setting "backcolor" (255, 0, 0)
Optionally you can declare the list of all your settings,
in that case the application will also save the default
values in the configuration file, but commented out:
fontSize=16
# dateFormat="%x"
# backcolor=(255,0,0)
If you do not specify the list of settings, only the
first line would be present in the configuration file.
With an ordinary setting, one row in the configuration file
means one setting. That setting may of course be a list
for instance. This setup works very well for shorter lists
like [1,2,3], however if you have a list of more complex
items, you will get very long lines and a configuration
file very difficult to edit by hand.
For these special cases there is also the ListSetting
constructor:
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"
Which is much more handy for big lists. An empty list is represented
like so:
testList=
There is also another technique that you can use if you have too long
lines: you can put line breaks in the setting values if you start the
following lines with a leading space, like so:
testList=["list1",
"list2", "list3"]
In that case don't use the ListSetting option. Any character after the
the leading space in the next lines will go in the setting value. Note
that the library will automatically wrap setting values longer than 80
characters when saving.
Once we declared the settings, we can read the configuration
from disk (and your settings module should export your wrapper
around the function offered by this library):
readResult <- try $ readSettings (AutoFromAppName "test")
case readResult of
Right (conf, GetSetting getSetting) -> do
let textSize = getSetting fontSize
saveSettings emptyDefaultConfig (AutoFromAppName "test") conf
Left (x :: SomeException) -> error "Error reading the config file!"
AutoFromAppName specifies where to save the configuration file.
And we've already covered the getSetting in this snippet, see
the readSettings documentation for further information.
You can also look at the tests of the library on the github project for sample use.
