Can form be embedded in a vertical viewport?

[amano-kenji]

What if form is too tall to fit in its given height? Does a form element make a visibility request?

Maybe, I'm supposed to split one form into multiple forms and make a visibility request for each one?

[jtdaugherty]

What if form is too tall to fit in its given height?

This is a bit unrelated to the viewport question, but for this question, the answer is that the form will only render what it can, from to bottom.

Does a form element make a visibility request?

No, but it would be pretty easy to add that in your application by using formFocus and visible to focus the currently-focused field in your drawing routine.

[jtdaugherty]

What I mean is that you'd augment the renderForm call with a call to visible, then wrap the whole thing in viewport. That will cause the viewport to scroll (if necessary) to make the selected form field visible. To get the required resource name, you'd use formFocus and focusGetCurrent to get the name of the focused field and pass that to visible. So something like this:

draw :: s -> Widget n
draw s =
    viewport ... $
    makeVisible $
    renderForm ...
    where
        makeVisible = case focusGetCurrent (formFocus f) of
            Nothing -> id
            Just n -> visible n 

[amano-kenji]

visible :: Widget n -> Widget n. n is not Widget n. Thus, visible n is wrong.

[amano-kenji]

makeVisible :: Ord n => n -> EventM n s (), so it cannot be used in rendering functions. But, you can use this in event handlers.

[amano-kenji]

I think I may have to render each form field separately. I don't know how to do that, yet.

[amano-kenji]

FormField
formFieldRender :: Bool -> b -> Widget n
A function to render this form field. Parameters are whether the field is currently focused, followed by the field state.

If I can customize this, then I can use the boolean parameter to decide whether to wrap a widget in visible.

[jtdaugherty]

visible :: Widget n -> Widget n. n is not Widget n. Thus, visible n is wrong.

Ah yes, sorry about that. visible w means "make w visible if you can."

makeVisible :: Ord n => n -> EventM n s (), so it cannot be used in rendering functions. But, you can use this in event handlers.

I think this is actually what I was thinking of, and I forgot the exact type. Since you can just as easily access the form state in your event handler, this is probably the best way to go.

[amano-kenji]

Requesting visibility in EventM is going to require boilerplate in multiple places. Doing it in RenderM is a lot cleaner.

For example, visible should be called in resize event and keyboard event.

[jtdaugherty]

For example, visible should be called in resize event and keyboard event.

Yeah, that should be just two places.

In any case, I'll update the form implementation to issue a visibility request for the focused field and include that in the next release.

[jtdaugherty]

In case you want to use the change now instead of waiting for a release, it's on master in cd8fce1.

[amano-kenji]

Much appreciated.

[amano-kenji]

Ater research, I discovered that lens cannot penetrate existential data types like FormFieldState.

I should limit existential data types to terminal data types that have no product data types.

DerivieGeneric for existential data types implies generic lens for existential data types. Thus, I consider it an open-ended research problem.