-- Extended function to return the result of op1 op op2
-- op1, op2 are operands
-- op is an operator: {+,-,*,/}
function calculate (op1, op2, op)
  if not uMatch.start_with_space() then return false end
  if     op == "+" then return tostring(op1 + op2)
  elseif op == "-" then return tostring(op1 - op2)
  elseif op == "*" then return tostring(op1 * op2)
  elseif op == "/" then return tostring(op1 / op2)
  else                  return false
  end
end
