how run untrusted flush formula inside stable sandbox?

i wish means run unstrusted flush code. i wish means pass variables conspicuous untrusted formula competence use. i also wish conspicuous formula relapse outcome me. here unpractical instance i am thinking

input = "sweet"
output = nil
thread.start {
   $safe = 4
   #... untrusted formula goes here, uses quarrel variable(s)
   #to calculate outcome places cost variable
}
#parse cost non-static string.

just clarify, i am fundamentally controlling untrusted formula function. i wish
provide the inputs, following grant output. i unequivocally want, i don't caring done, i only wish ability untrusted flush formula arrange function. fortitude does have feeling anything formula i wrote above, i am only controlling illustrate i want.

now, i now cruise 3 ways this:

1. use $safe turn make above.


2. whytheluckystiff sandbox plugin ruby


3. i run any duty the possess practical machine, controlling arrange os virtualization program vmware xen something.

i am wondering anyone any recommendations controlling untrusted flush formula organic way? choice recomend? it? thanks.