Brick Form as Modal Windows

[Aumarre]

Hello,

I must be doing something wrong. I would like to use Brick.Forms as a modal popup in a “Brick” application, but I can't find anywhere how to do this. Is it even possible?

In the record containing the application status, I include a declaration of the type

field :: forall e. Form FormState e AppResourceName

where FormState represents the type associated with the form data, AppResourceName represents the type associated with resource names, and “e” represents the type of events.

I have created the associated lenses, but I get an error when I “zoom” on the “field” field to process events.

Do you have any idea what is missing?

Thank you in advance, and sorry if this question is not posted in the right place.

Olivier

Translated with DeepL.com (free version)

[jtdaugherty]

Hi!

I must be doing something wrong. I would like to use Brick.Forms as a modal popup in a “Brick” application, but I can't find anywhere how to do this. Is it even possible?

Yes, this is possible, but you'll need to build the infrastructure to do it. There are a few moving parts. Here are some thoughts on how this can be done:

• You'll need a way to tell at event handling and drawing time whether you are in the modal window. A common way in my experience is to have data Mode = Main | ModalWindow | ..., store a Mode in your application state, modify that mode when the application mode changes (e.g. to start showing or hide your modal window), and dispatch on that mode to make drawing decisions.
• Add an application state field to carry your processed modal window results. Its type would be your form state type. You might wrap it in Maybe so that you don't have to keep it populated before your window is shown.
• Add another application state field to carry the Form itself. For this, you shouldn't need an existential as you used above; that will just create headaches, unless you really need things to be that generic.

Once you have those bits in place, it should be pretty straightforward to know when to draw the modal window with your form in it, how to dispatch incoming events, and where to put the form's final state once it's validated.

[Aumarre]

Thank you for your reply. But now I'm stuck with the Form type declaration in the application state.

When I write

field :: Form FormState e AppResourceName

in the definition of the ‘State’ type, I get an error saying ‘Not in scope: type variable “e”’.

That's why I declared ‘forall e’...

Is there a specific configuration that needs to be set up (cabal file, pragma, etc.)? I don't see what the exact type of events is.

Do you have an example? I feel like I'm going round in circles. I'm sure I'm doing something ‘wrong’, but I can't figure out what it is. I'm still learning a lot about Haskell!

Once again, thank you in advance for your help.

[jtdaugherty]

I'm not sure I understand why you would like your form to be polymorphic in its event type. That type usually should match the concrete type your application is already using for its events; so if you have App s e n, your form's event type e should be the same e as used in your App.

[Aumarre]

Here is an excerpt from the code to help better understand my problem. The “e” in the myForm field generates an error (Not in scope: type variable “e”), and I don't see what type to put here. In this type, I also have a Dialog type that works normally.

For the record, I want to display a Form on top of a Brick application (in this case, only the entry of a numeric value with two buttons, Yes and No). .

I tried putting () instead of “e,” but although the Form displays correctly (but clears the screen), I can't process the events. I get an error when I do a “zoom myForm $ handleFormEvent ev”

Types declarations

data FormState = FormState {
    _value :: Int
}
deriving (Show)

data TuiState = TuiState {
    …
    -- The problem “e” is not recognized!
    _myForm :: Form FormState e TuiControlNames
    …
}

makeLenses ''FormState
makeLenses ''TuiState

Functions

tuiInitialize = 
    do
        …
        -- Some code
        …
    void $ defaultMain  
            tuiApp
            (TuiState {
                …
                myForm = createMyForm …
				…
                }
            )


tuiApp = App TuiState e TuiControlNames
tuiApp = 
    App 
    {
        appDraw = tuiDraw,
		appChooseCursor = tuiAppCursor,
        appHandleEvent = tuiAppEvent,
        appStartEvent = do
            vty <- getVtyHandle
            liofIO $ setMode (outputIFace vty) Mouse True,
        appAttrMap = const tuiAttrMap
    }

[jtdaugherty]

Using () is the appropriate thing to do here, since you are not using any custom event type of your own. You'll need to make sure that the e is () everywhere, including in the field type of your TuiState.

[Aumarre]

Thank you so much for your help, I understand my mistake now !

And by using “()” as type “e,” everything is back to normal.

[jtdaugherty]

Wonderful, I'm glad to hear it!