[Haskell-cafe] Number of widgets extant and displayed varying over time? (FRP, reactive-banana)

Jeffrey Brown jeffbrown.the at gmail.com
Wed Jan 14 02:39:25 UTC 2015

Dear list,

I want to write an application in which the set of widgets in existence,
and the subset of them that is displayed, depends on user input. I am using
reactive-banana. So far the simplest spec I have imagined for it is this:

    Initially there is just a text entry box and an empty (hence invisible)
collection of labels.

    The user can do two things: enter the word "add", or enter an integer.

    Entering the word "add" causes a label to be added to the collection,
but not displayed. The labels require no text content.

    Entering an integer N causes the first N labels to be displayed
onscreen. The text entry box remains visible.

I am totally baffled. In particular, the Behavior paradigm, though it is
elegant and beautiful whenever I study it, I have no idea how to apply.

Thank you,
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