I meant the "returned expression" not the "return statement"!

it's effectively

return scalar(10,20);
[download]

so no warning

  DB<100> print scalar (10,20)
20
[download]

UPDATE: maybe the following is clearer,

  
  DB<113> sub tst { 2..10 }
 => 0
 
  DB<114> ($a)=tst()
 => 2
  
  DB<115> $a=tst()
 => ""
 
  DB<116> sub tst { /2/../10/ }
 => 0
 
  DB<117> $_=2
 => 2
 
  DB<118> $a=tst()
 => 1
 
  DB<119> $a=tst()
 => 2
 
  DB<120> $_=10
 => 10
 
  DB<121> $a=tst()
 => "3E0"
[download]

as you can see the range-op transforms to flip-flop-op in scalar context.

So we are not returning a list but an expression which is evaluated according to the callers context.