How to sampleOn signal and keep the sampled value in Elm?

Question

Consider a model:

model : Signal Model

and the following 2 signals:

clickPosition = Mouse.position
  |> Signal.sampleOn Mouse.clicks

and:

dimensions = Window.dimensions

I'd like to get the following desiredSignal:

            (0,0)       (30,20)               (60,70)
clickPosition +------------+---------------------+---------

              M0   M1                  M2     M3
        model +----+-------------------+------+------------

          (600,800)         (400,300)  (200,800)
   dimensions +-----------------+----------+---------------

              D1           D2                    D3
desiredSignal +------------+---------------------+---------


where:

  D1 = ((0,0), M0, (600,800))
  D2 = ((30,20), M1, (600,800))
  D3 = ((60,70), M3, (200,800))

i.e. I'd like to sampleOn clickPosition, but keep the sampled value.

How could I do that?

score 3 · Accepted Answer · answered Nov 04 '15 at 11:02

3

It looks like your desiredSignal is the latest value of the three signals, tupled, but only changing on a change from the clickPosition signal. You can do this by first combining them, and then sampling on the clickPosition signal:

desiredSignal =
  Signal.map3 (,,) clickPosition model dimensions
  |> Signal.sampleOn clickPosition

answered Nov 04 '15 at 11:02

Apanatshka

5,958
27
38

Aha! For some reason, I thought that if I sampleOn `clickPosition` then it shouldn't be involved in the mapping. Makes perfect sense now, Thanks! – Misha Moroshko Nov 04 '15 at 11:09

How to sampleOn signal and keep the sampled value in Elm?

1 Answers1