try_require

try_require.lua

function try_require(module_name)
    local success, module = pcall(require, module_name)
    local first_time = true

    return function()
        if success and first_time then
            first_time = false
            return module
        end
    end
end

for foo in try_require 'foo' do
    local x = foo.do_stuff()
    print(x)
    -- whatever
end

with_require.lua

function with_require(module_name, action)
    local success, module = pcall(require, module_name)
    if success then
        return action(module)
    end
end

with_require('foo', function(foo)
    local x = foo.do_stuff()
    print(x)
    -- whatever
end)

-- This seems less flexible