Lua with NeoVim: Modules and Require — local M = {}, return M & require() | Episode 24

Lua with NeoVim: Modules and Require — local M = {}, return M & require()

In Lua, organizing code into reusable modules is essential for building real-world programs. This tutorial demonstrates the standard Lua module pattern by creating a table M, attaching functions to it, returning M to export the module, and then loading it in another script using require(). We build a simple math tools module and use it side-by-side in NeoVim splits to illustrate modular programming and code reuse.

Code

-- mathtools.lua: Define a module with math functions
local M = {}  -- module table

function M.add(a, b)
  return a + b
end

function M.subtract(a, b)
  return a - b
end

function M.multiply(a, b)
  return a * b
end

function M.square(x)
  return x * x
end

function M.is_even(n)
  return n % 2 == 0
end

return M  -- export the module


-- main.lua: Load and use the mathtools module
local mt = require("mathtools")  -- load the module

print("Add 2 + 3 = " .. mt.add(2, 3))
print("Subtract 5 - 1 = " .. mt.subtract(5, 1))
print("Multiply 4 * 6 = " .. mt.multiply(4, 6))
print("Square of 7 = " .. mt.square(7))

local n = 10
print("Is " .. n .. " even? " .. tostring(mt.is_even(n)))  -- tostring converts boolean to string for concatenation

Key Points

• The module pattern uses a local table M to hold functions and data to be exported.
• Functions are attached as fields on M (e.g., M.add) to expose them outside the module.
• Returning M at the end of the file exports the module for use with require().
• require("module") loads, runs, and caches the module, returning the exported table.
• Use tostring() to convert boolean results to strings when concatenating for output.