"Expected whitespace character" when running a custom inputKey - scala

Question

I am creating a custom inputKey which looks like
val rating = inputKey[Option[Int]]("How will you rate this course?")
rating := {
import complete.DefaultParsers._
import complete.Parser
val r: Parser[Int] = IntBasic.examples("<rating>")
r.result
}
This sits in file projectRoot/build.sbt.
I try to run this on sbt shell using multiple times, each time it fails
sbt:Hello> rating 1
[error] Expected whitespace character
[error] Expected '/'
[error] rating 1
[error] ^
sbt:Hello>
Then,
sbt:Hello> show "rating 3"
[error] Expected whitespace character
[error] Expected 'Global'
[error] Expected '*'
[error] Expected 'Zero'
[error] Expected 'ThisBuild'
[error] Expected 'ProjectRef('
[error] Expected '{'
[error] Expected project ID
[error] Expected configuration
[error] Expected configuration ident
[error] Expected key
[error] show "rating 3"
[error] ^
sbt:Hello>
Also, as
sbt:Hello> rating "5"
[error] Expected whitespace character
[error] Expected '/'
[error] rating "5"
[error] ^
sbt:Hello>
I do not know what I am missing here. Can someone please point out my mistake here?

Answer 1

Since there is a space character before the integer, try using Space ~> IntBasic parser combination like so
lazy val rating = inputKey[Int]("How will you rate this course?")
rating := {
import complete.DefaultParsers._
val rating = (Space ~> IntBasic).examples("<rating>").parsed
println(s"Rating input = $rating")
rating
}
Executing rating 3 in sbt should now output Rating input = 3