When you get a message like "print (...) interpreted as function ...", you can typically disambiguate your statement for Perl by simply adding a + in front of the opening parenthesis.

Your original code runs like this:

ken@ganymede: ~/local/bin
$ perl -Mstrict -Mwarnings -E 'my $s = "foo bar baz qux 3 3 1 3"; my @
+a = split /\s/, $s; splice(@a, 0, 4); while (@a) { print (shift @a), 
+(shift @a), "\n"; }'
print (...) interpreted as function at -e line 1.
Useless use of a constant (
) in void context at -e line 1.
31ken@ganymede: ~/local/bin
$
[download]

Adding a single + (changing ... print (... to ... print +(...), you get the output you were after:

ken@ganymede: ~/local/bin
$ perl -Mstrict -Mwarnings -E 'my $s = "foo bar baz qux 3 3 1 3"; my @
+a = split /\s/, $s; splice(@a, 0, 4); while (@a) { print +(shift @a),
+ (shift @a), "\n"; }'
33
13
ken@ganymede: ~/local/bin
$
[download]

This is discussed in more detail in perlop - Symbolic Unary Operators.