Added support for lists.
Operator ~ for strings will invert case.

$ ./neo
neo] a = { 10, 20, 30, 40 }
{10,20,30,40 } length=4
neo] b = { 90, 100, 'Apple' }
{90,100,'Apple' length=5 } length=3
neo] c = a + b
{10,20,30,40,90,100,'Apple' length=5 } length=7
neo] ~ 'orange'
'ORANGE' length=6
neo] quit

$