Sum of squares

say [+] map * ** 2, (3, 1, 4, 1, 5, 9);

If this expression seems puzzling, note that * ** 2 is equivalent to {$^x ** 2}— the leftmost asterisk is not the multiplication operator but the Whatever star, which specifies currying behavior. Another convenient way to distribute the exponentiation is via the cross metaoperator, which as a list infix is looser than comma in precedence but tighter than the reduction list operator:

say [+] <3 1 4 1 5 9> X** 2