I thought the same thing, but it doesn't seem so:

#!/usr/bin/perl -w

use List::Util qw[ reduce ];

print reduce{ print "a = '$a', b = '$b'\n"; eval "showcontext($a + $b)
+";} 1,2,3;

sub showcontext
{
  print "Context: ";
  if (wantarray) {
    print "array\n";
  }
  elsif (defined(wantarray)) {
    print "scalar\n";
  }
  else {
    print "void\n";
  }
  $_[0];
}
[download]

produces:

$ perl /tmp/t76
a = '1', b = '2'
Context: scalar
Use of uninitialized value in concatenation (.) or string at /tmp/t76 line 5.
a = '', b = '3'
Use of uninitialized value in concatenation (.) or string at /tmp/t76 line 5.
Context: scalar
3