Consider adding .=(a:Arr, field:Str, mapper:Fun)

[ilyash-b]

So that this:

sessions.each(F(s) {
   s.COMPUTE_STACK_PRESENT = if s.ComputeStackName then s.ComputeStackName in stacks_names
})

could become this:

sessions.COMPUTE_STACK_PRESENT = F(s) if s.ComputeStackName then s.ComputeStackName in stacks_names