Discarded non-Unit value?

[michalrus]

Take this code:

var button = slot[Button]
button <~ On.click { button <~ hide }

… and compile it with -Ywarn-value-discard (useful flag!) using the 2.11.8 compiler.

It fails with:

[error] /home/m/Development/[…]/TestActivity.scala:19: discarded non-Unit value
[error]     button <~ On.click { button <~ show }
[error]                        ^
[error] one error found