About reference transparency being broken and whether or not to modify this package.

[yukikurage]

First, every function.

tmp = every 1000.0

main :: Effect Unit
main = launchAff_ do
  Aff.delay $ Milliseconds 500.0
  let
    pulse = tmp
  liftEffect $ runSignal $ pulse ~> logShow

outputs

75.52480700612068
1076.4696190059185
2078.1452220082283
3079.518830999732
4080.8751610070467
5081.603973001242
...

main :: Effect Unit
main = launchAff_ do
  Aff.delay $ Milliseconds 500.0
  let
    pulse = every 1000.0
  liftEffect $ runSignal $ pulse ~> logShow

outputs

578.351668998599
1580.3739890009165
2580.902148991823
3582.3207959979773
4583.194288998842
...

These behaviors are different, but what we have done is replace the bindings.

Next, merge function

main :: Effect Unit
main = do
  channel1 <- channel true
  channel2 <- channel true
  let
    mergedSignal = merge (subscribe channel1) (subscribe channel2)
  send channel2 false
  logShow =<< get mergedSignal

output false

main :: Effect Unit
main = do
  channel1 <- channel true
  channel2 <- channel true
  send channel2 false
  let
    mergedSignal = merge (subscribe channel1) (subscribe channel2)
  logShow =<< get mergedSignal

outputs true

For the same reason, filters are not referentially transparent either.

I would like to modify these APIs, but in fact, this package references Elm's APIs, so it may not be a good idea to make direct changes. In other words, there are two options

• Modify the this Signal package
• Create a new, modified package

Do you have any suggestions on the pros and cons of modifying this package, or any other suggestions?