how to merge two signals with SampleOn in Elm

I try to merge two signals. One is Mouse.clicks and another is Keyboard.space.

On clicks, I should get a Signal(Int,Int) from Mouse.position as return value
On space, I should get something different so I can identify different signal is triggered.

My idea is:

type Event = Click | Space

mergedSignal : Signal Event
mergedSignal = 
  let
    clickSignal = map (\event -> Click) Mouse.clicks
    timeoutSignal = map (\event -> Space) Keyboard.space
  in
    merge clickSignal timeoutSignal

and get position somehow:

positionOnClickSignal:Signal (Int,Int)
positionOnClickSignal = sampleOn Mouse.clicks Mouse.position

Obviously, it is wrong.

Solution

It sounds like you want the mouse position to carry over as part of the event. In that case, you could redefine Event as

type Event
  = Click (Int, Int)
  | Space

Inside your mergedSignal, the clickSignal is currently just checking for Mouse.clicks but based on your description and other example, I think you actually want that to be based off positionOnclickSignal, which gives you a Signal (Int, Int), and using that, you can now populate the (Int, Int) portion of the Click (Int, Int) event like this:

clickSignal =
  map Click positionOnClickSignal

You'll notice that I took out the parenthesis in the above. That is more idiomatic for Elm, because Click is in essence a function that takes one (Int, Int) parameter, which will be passed in from the map function. It could have easily been written like this:

clickSignal =
  map (\pos -> Click pos) positionOnClickSignal

Now, if you're just trying to see some debug text of this on screen, a quick and easy way to go about that is to use show from the Graphics.Element package.

import Graphics.Element exposing (show)

main =
  map (show << toString) mergedSignal

That will give you some debug text shown as the only thing on the page, and you could easily toss it up on http://elm-lang.org/try for testing.