Alternative prompt / defered signals

This is an experimental package: I wanted to see what an alternative world would look like where Elm distinguished between defered signals (signals that start out "empty") and prompt signals (signals that are created with an initial value in the first position).

Disclaimer

This is an experiment - please don't use it in production. It's probably not very performant to use foldl on either prompt or defered signals right now since there is quite a lot of magic making this work...

Usage

Use Signal.foldl like you would List.foldl or Array.foldl

import Signal.Extra       -- See Apanatshka/elm-signal-extra

Signal.foldl f x signal == Signal.Extra.foldp' f (flip f x) signal

Defered.foldl is similar to Signal.foldp except that a foldl-like seed value is used, instead of an initial value.

Signal.foldp f (f initial seed) signal == prompt (f initial seed) (Defered.foldl f seed (defer signal))

Defered.foldl relates to Signal.foldl as follows.

prompt initial (Defered.foldl f seed defsig) == Signal.foldl f (prompt (f initial seed) defsig)

Examples

Sometimes it is not clear that a signal what the initial value of a signal should be. One example is a mouse click, a discrete signal that appears to trigger only on after initialization has completed. This is called a defered signal in this library, I.e. Defered.Signal ()

import Signal.Alt as Signal
import Signal.Alt (Signal)
import Signal.Defered as Defered
import Mouse.Defered as Mouse

-- Produces a defered signal that looks like this: <1,2,3,4,5,...>
clicksCounter : Defered.Signal Int
clicksCounter = Defered.foldl (\c -> c + 1) 0 Mouse.clicks

-- Produces a prompt signal that looks like this: <Nothing,Just "1",Just "2",Just "3",Just "4",Just "5",...>
displayedClicks : Signal Int
displayedClicks = Singal.prompt Nothing <| (Just << toString <~ clicksCounter)