OpenEuphoria

Yes, I was thinking of that, but I'm not yet sure of practical that might be.

Here is an obviously contrived example, but it does highlight problems with functions that return different structures based on the input data.

function FUNC(object x) 
  if x > 0 then 
      return {x, {x * x, sqrt(x)}} 
  elsif x = 0 then 
      return x 
  else 
      return {-x, x * x} 
  end if 
end function 
 
{a,{b,c}} = FUNC( userdata )