← Back to context

Comment by mrkeen

11 hours ago

No, they are function colouring. That's the point.

Someone writes a post lamenting red and blue functions, and everyone eats it up.

Substitute colour for something meaningful and the idea becomes idiotic.

"Top level function declares that it is non-blocking, but when I try to call a small blocking function from it, I have to change the declaration to blocking???"

Yes, yes you do.

Total functions can't call non-total functions.

Deterministic functions can't call nondeterministic functions.

Non-IO functions can't call IO functions.

7 comments

mrkeen

Reply
captaincrowbar  9 hours ago

‘Non-IO functions can't call IO functions.’

How do you handle logging then? If f() calls g(), how can I add logging to g() without having to change or recompile f() (and everything in the call stack above it)? ‘You can’t’ is not an acceptable answer.

  • tome  8 hours ago

    Not sure why people are saying "you can't" when it seems to me the whole point of algebraic effects that you can. You can define g so that it has no ability to do "general IO", all it can do is yield log messages. Then f can call g in a way that turns the log messages into writes to stdout. For example, here's how you would do it in Bluefin:

        type Log = Yield String
    
    -- workWithLogging cannot do arbitrary IO!
    -- All it can do is yield log messages, which
    -- must be processed elsewhere.
    workWithLogging  ::
      (e1 :> es) =>
      Log e1 ->
      Int ->
      Int ->
      Eff es Int
    workWithLogging l x y = do
      yield l ("x was " <> show x)
      yield l ("y was " <> show y)
      let result = x + y
      yield l ("result was " <> show result)
      pure result
    
    -- ghci> example
    -- x was 5
    -- y was 7
    -- result was 12
    -- 12
    example :: IO Int
    example = runEff $ \io -> do
      -- forEach determines how each log message
      -- should be handled.
      forEach
        (\l-> workWithLogging l 5 7)
        (\logMsg -> effIO io (putStrLn logMsg))

  • CuriousSkeptic  8 hours ago

    You can’t is an acceptable answer. The entitle point of such a feature is to prevent people from doing that.