[Haskell-cafe] Idea for a very simple GUI llibrary

[Keith Holman]

You should also check out Fudgets and "Tangible Functional
Programming." Fudgets is a really old Haskell UI library concept;
Tangible FP is a recent Google talk about a UI library inspired by
Haskell types.

2009/11/22 Luke Palmer <lrpalmer at gmail.com>:
> Nice idea.  I will try it if you write runGUI :-)
>
> This is an imperative style library.  For more Haskellian GUI library
> ideas, see Fruit (http://www.haskell.org/fruit/) and TVs
> (http://www.haskell.org/haskellwiki/TV).  They may not pass the
> "builds" constraint :-P
>
> Luke
>
> 2009/11/22 Maurí­cio CA <mauricio.antunes at gmail.com>:
>> Hi,
>>
>> Here is a sketch for a library with these properties:
>>
>> -> Easy to test. All Haskell code can be tested in a text
>> terminal. Also, testing code that uses the library can also be
>> done without using a GUI.
>>
>> -> Extremely easy to document and use.
>>
>> -> Not even close to Gtk2hs power, but enough for small
>> applications.
>>
>> -> Could be the first GUI to build on hackage :)
>>
>> What we need is:
>>
>> -> MyState. A user suplied type for application state.
>>
>> -> WidId. A user suplied type for widget identifiers.
>>
>> -> Gui wi. A type capable of describing an interface with all of
>> its state. It's an instance of Eq.
>>
>> -> Event wi. A type for events.
>>
>> -> Prop. A type for properties than can related to a WidId.
>>
>> Running an application would be like this:
>>
>> main = runGUI
>>        initState  -- An initial MyState.
>>        event      -- :: MyState -> DiffTime -> Event WidId -> MyState
>>        props      -- :: WidId -> [Prop]
>>        action     -- :: MyState -> DiffTime -> IO (Maybe (MyState,Gui
>> WidId))
>>        timeout    -- :: DiffTime
>>
>> DiffTime parameters for callbacks are always the time elapsed
>> since application started.
>>
>> From initState and event, the implementation of runGUI can save a
>> state that optionally changes with time.
>>
>> From props, it can get details on what to present in widgets
>> associated with a WidId (selected state, picture to draw etc.).
>>
>> action presents a chance for using IO, and optionally change state
>> and GUI description.
>>
>> timeout is the maximum time runGUI implementation is allowed to
>> wait between calls to action.
>>
>> Examples for those types:
>>
>> newtype MyState = {
>>    lastUpdate :: DiffTime,
>>    builtGui :: Bool,
>>    earthCoordinates :: (Double,Double),
>>    map :: SVG,
>>    ...
>>  }
>>
>> data WidId = XCoord | YCoord | MapWindow | ReloadButton ...
>>
>> data Gui widid = TitleWindow (Gui widid)
>>      | Tabs [(String,Gui widid)]
>>      | PressButton String widid
>>      | Selection [String] widid
>>      | ...
>>  deriving Eq
>>   {-
>>      Eq is needed by runGUI to detect if GUI has
>>      changed after the last call to action.
>>   -}
>>
>> data Event widid = ButtonPressed widid
>>      | FileSelected String widid
>>      | OptionSelected String widid
>>      | ...
>>
>> data Prop widid = Active Bool
>>      | Text String
>>      | Draw SVG
>>      | ...
>>
>> I believe this can represent most kinds of simple applications,
>> and be efficient enough for practical use.
>>
>> It's interesting that all of this can be designed, implemented and
>> tested independent of runGUI implementation. Actually, if you want
>> a pet project and want to write and design the Haskell part, I may
>> probably be able to write runGUI for you :)
>>
>> Best,
>> Maurício
>>
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