Hey Yotam,

Pattern matching clauses evaluate from left to right. You can get the behavour you're after by swapping the arguments in the tuple:

case (stop, infi) of
  (Just _, Nothing) -> 1
  (_, _) -> 2

Evaluates to 2

On Tue, 20 Jun. 2017, 7:29 pm Yotam Ohad, <yotam2206@gmail.com> wrote:

Hi,

After reading "Push-Pull Functional Reactive Programming" I had an idea about deciding which, of two events, comes first. Instead of using forkIO, I tried something like the following:

infi :: Maybe Int

infi = infi

stop :: Maybe Int

stop = Nothing

test :: Int

test = case (infi, stop) of

    (Nothing, Just _) -> 1

    (_, _) -> 2

Here, infi is an action that never ends, and stop a function that ends immediately. I thought that the compiler would see that stop evaluates immediately to Nothing and thus will return 2, but it tries to evaluate infi and get stuck.

I think it happens because I am using a tuple to hold both values (but not really sure about it). Do you know a way to make this arrangement work?

Yotam

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