error raises. pcall catches.

Goal

Catch a thrown error and print it.

local ok, err = pcall(function()
  error("empty till")
end)
print(ok)
print(err)

local ok, result = pcall(function()
  return 12 * 40
end)
print(ok, result)

local function need_city(city)
  if city == nil or city == "" then
    error("city required")
  end
  return city
end
print(need_city("Nairobi"))
local ok, err = pcall(need_city, "")
print(ok)
print(err)

print(pcall(function() return 1 + 1 end))