Effekt program ran with `effekt` executes IO operations in incorrect order

[timsueberkrueb]

Consider the following program:

import stringbuffer

def prompt_for_user_name(): String = {
  println("What's your name?")
  readln()
}

def main() = {
  val username = prompt_for_user_name()
  println(s"Hello ${username}")
}

Output:

> ./out/foo
What's your name?
xxx
Hello xxx
> effekt foo.effekt
xxx
What's your name?
Hello xxx

[b-studios]

Really bad publicity for a language that's called Effekt ;)

This is probably also related to all the jvm / sbt io piping that @marzipankaiser had to go through

[jiribenes]

We talked about this being potentially bad multiple times in #981 which added it:

The biggest potential issues here are flushing & the interaction between readln and println. The following program should first print the prompt, then read the user's input, and then finally print the output.

def main() = {
  println("What's your name?") // prompt
  val name = readln()
  println("Hello, " ++ name ++ "!")
}

And then @marzipankaiser already reported on the PR that it does not work on LLVM with #982 which already fixed (or tried to fix) the jvm/sbt-related flushing — but yeah, it looks like something to do with flushing...