The Scala REPL output is confusing
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Raphael Bosshard
Oct 31, 2016, 4:51:07 PM10/31/16
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Hi all,
have you ever noticed how confusing the Scala REPL output it?
I have learned what this "foo: (in: String)Int) is supposed to mean. But from a beginner's perspective I find it puzzling. Instead it should display something like this:
Cheers,
Raphael
have you ever noticed how confusing the Scala REPL output it?
scala> def foo(in: String): Int = ???
foo: (in: String)Int
I have learned what this "foo: (in: String)Int) is supposed to mean. But from a beginner's perspective I find it puzzling. Instead it should display something like this:
method created: foo(in: String): Int
Cheers,
Raphael
Oliver Ruebenacker
Oct 31, 2016, 4:55:16 PM10/31/16
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Justin du coeur
Oct 31, 2016, 5:11:11 PM10/31/16
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(Note that this conversation started over on Gitter, and moved here.)
That's fair, but note that the output isn't legal Scala. The "method created" bit I agree is arguable, but it really is kind of weird and confusing that there's no colon before "Int" in the output -- the output syntax seems strangely arbitrary. Was there a specific reason for that, or is it just an old "seemed good enough at the time"?
I should note that I don't care passionately -- I don't use the REPL much myself. But this seems like a pointless roadbump for new users, having the output be almost, but not quite, legal Scala.
And really, is "unnecessary clutter" (at least in small amounts) actually a problem in the REPL? I would say that clarity is likely a higher priority than output conciseness...
Oliver Ruebenacker
Oct 31, 2016, 5:55:41 PM10/31/16
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Adriaan Moors
Oct 31, 2016, 6:46:14 PM10/31/16
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I agree the output would be nicer if we printed out the method definition in legal Scala. The current output is just printing the (strictly) internal representation of a method type.
I would be happy to help to improve this. I believe the logic for the output is here: https://github.com/scala/scala/blob/2.12.x/src/repl/scala/tools/nsc/interpreter/MemberHandlers.scala#L156
cheers
adriaan
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Naftoli Gugenheim
Oct 31, 2016, 9:58:23 PM10/31/16
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Could this be solved the easiest with scala.meta?
Adriaan Moors
Oct 31, 2016, 10:56:39 PM10/31/16
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I think everything needed is available from the compiler. Formatting this nicely (especially with colors) is a bit finicky, but I don't think meta would really help here.
Heather Miller
Nov 1, 2016, 5:47:46 AM11/1/16
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+1 to improving the REPL output such that it prints out the Scala method definition. I'd love to see this.
(I've always wondered why the REPL output wasn't friendlier!)
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Oliver Ruebenacker
Nov 1, 2016, 10:28:39 AM11/1/16
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So, what you want as REPL echo would be exactly what the user entered, except maybe with white space adjusted and return type added, right?
Heather Miller
Nov 1, 2016, 10:51:38 AM11/1/16
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Not exactly what was entered. Just the normal signature of what was entered. No body of the method, of course.
So for the example the OP started with, we print this now:
foo: (in: String)Int
I understood that we'd print this instead:
def foo(in: String): Int
Oliver Ruebenacker
Nov 1, 2016, 11:14:41 AM11/1/16
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Right, not the body. Otherwise, essentially what the user entered, right?
Justin du coeur
Nov 1, 2016, 12:02:19 PM11/1/16
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Basically, yes. Which is why a prefixing message of "Created" would be beneficial, but even without that it would be less mystifying than the current output...
Raphael Bosshard
Nov 1, 2016, 12:41:06 PM11/1/16
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Excellent. I'll give it a shot and come back if I need help. Do I need to create a PR for that?
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Adriaan Moors
Nov 1, 2016, 12:58:05 PM11/1/16
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Yes, a PR will be needed for the CI to verify your changes. We have some docs (https://github.com/scala/scala/blob/2.12.x/README.md, http://scala-lang.org/contribute/hacker-guide.html) to help you get started, and are always happy to help on https://gitter.im/scala/contributors!
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Raphael Bosshard
Nov 3, 2016, 7:55:07 AM11/3/16
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Hi all,
This is now https://issues.scala-lang.org/browse/SI-10023. We can discuss the specifics (i.e. how the new output should look like) there.
Thanks for all the help and directions!
Raphael
This is now https://issues.scala-lang.org/browse/SI-10023. We can discuss the specifics (i.e. how the new output should look like) there.
Thanks for all the help and directions!
Raphael
som-snytt
Nov 5, 2016, 2:31:57 AM11/5/16
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I already responded to the cross-posting elsewhere -- that different users have different needs --
but Oliver's comment reminded me that the clever `//print` autocomplete mechanism is easy to overlook.
I'd like an output mode for REPL where it's basically doing what //print does. That is, echo what I typed with extra type info.
The only difference is that //print would not side-effect, but nobody does that anyway.
For example, when I enter f(17), show me the expanded expression.
scala> def f(i: Int)(implicit j: Int) = i + j
f: (i: Int)(implicit j: Int)Int
scala> implicit val x: Int = 42
x: Int = 42
scala> f(17) //print
$line4.$read.$iw.$iw.f(17)($line5.$read.$iw.$iw.x) // : Int
scala> f(17)
res0: Int = 59
Jasper-M
Nov 7, 2016, 6:45:17 AM11/7/16
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I don't really have a problem with the output of method types and such in the REPL. But might it be an idea to trim all the $wrapper stuff from the output of //print ?
Op zaterdag 5 november 2016 07:31:57 UTC+1 schreef som-snytt:
Op zaterdag 5 november 2016 07:31:57 UTC+1 schreef som-snytt:
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