Kotlin forEach sometimes not executing until CTL-C when run in the REPL?

Question

When running the following code as a snippet from https://www.programiz.com/kotlin-programming/examples/convert-list-array :

   
    // printing elements of the array list
    vowels_list.forEach { System.out.print(it) }


   // vowels array
    val vowels_array: Array<String> = arrayOf("a", "e", "i", "o", "u")
    
    // converting array to array list
    val vowels_list: List<String> = vowels_array.toList()
    
    // printing elements of the array list
    vowels_list.forEach { System.out.print(it) }

The output is supposed to be aeiou

However when I am running it in the kotlin REPL nothing is printed. Why is that?

Update There seems to be something going on for the kotlin repl itself. I just noticed there is a bracket - as if the code were not completed yet:

I have to hit CTL-C and then we see this:

aeiou<interrupted>

What is happening here?

The above code works fine for me in Kotlin REPL. I don't it's a problem with the code. It is probably an issue with your IDEA. This makes no sense but can you remove the comments and try again. It's a long shot — Xid, Jan 17 '21 at 20:29
I'm running this in the REPL - which is noted in the question. I'll add that to the title since it seems to be the real problem — WestCoastProjects, Jan 17 '21 at 20:31
The issue might be in the buffering of the terminal where you are running REPL. Try to add `println()` to the end of your code. — Konstantin Raspopov, Jan 17 '21 at 20:36
@KonstantinRaspopov OK yes that solved it. Please make that an answer — WestCoastProjects, Jan 17 '21 at 20:44

score 2 · Answer 1 · edited Jan 17 '21 at 20:33

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Did you try to run only the last three lines of code?
I did it by running on https://play.kotlinlang.org/ and it printed aeiou.

edited Jan 17 '21 at 20:33

DuDa

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answered Jan 17 '21 at 20:16

Eduard-Alexandru Codău

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Thanks for pointing out that it is working in a different environment. There seems to be something funny about `kotlin` REPL. See my question update – WestCoastProjects Jan 17 '21 at 20:23
I haven't worked REPL so far, I used the kotlin sandbox provided by JetBrains and I've coded kotlin projects in Intellij IDEA. – Eduard-Alexandru Codău Jan 17 '21 at 20:28

score 2 · Accepted Answer · answered Jan 17 '21 at 20:48

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The issue is in the buffering of the terminal. You may add println() to the end of your code to force flushing the symbols to the screen.

answered Jan 17 '21 at 20:48

Konstantin Raspopov

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btw Did you run into any way to disable output buffering in the REPL? – WestCoastProjects Jan 17 '21 at 20:59
@StephenBoesch as far as I know, there's no easy way to do it. Also, it depends on your OS. You can try some approaches from this question https://stackoverflow.com/q/3465619/2314529 – Konstantin Raspopov Jan 17 '21 at 21:24
This isn't specifically an REPL issue. It's very common for text output to be line-buffered; stdout is on most operating systems (though not stderr). So it's good practice to write a trailing newline character (e.g. by using `println()`). In fact, on Unix a text file is always assumed to end with a newline, and some tools may ignore anything after the last newline. – gidds Jan 17 '21 at 22:52

Kotlin forEach sometimes not executing until CTL-C when run in the REPL?

2 Answers2