Basic literate programming in Lua.

litlua.lua

local litlua = {}

-- String split function - taken from Penlight
-- https://github.com/stevedonovan/Penlight/blob/master/lua/pl/utils.lua#L172
local function split(s, re, plain, n)
    local i1, ls = 1, {}
    if not re then re = '%s+' end
    if re == '' then return {s} end
    while true do
        local i2, i3 = s:find(re, i1, plain)
        if not i2 then
            local last = s:sub(i1)
            if last ~= '' then table.insert(ls, last) end
            if #ls == 1 and ls[1] == '' then
                return {}
            else
                return ls
            end
        end
        table.insert(ls, s:sub(i1,i2-1))
        if n and #ls == n then
            ls[#ls] = s:sub(i1)
            return ls
        end
        i1 = i3+1
    end
end

-- Local helper function to check if a string is a prefix of another.
local function starts(str, start) return str:sub(1, start:len()) == start end

-- Transforms markdown into a lua file. It simply makes every non-codeblock line into a comment.
-- This preserves line numbers.
function litlua.transform(markdown)
	local lines = split(markdown, "[\r\n]")
	local output, inCodeBlock = "", false
	for _, line in ipairs(lines) do
		if inCodeBlock then
			if starts(line, "```") then inCodeBlock = false
			else output = output .. line .. "\n" end
		end

		if not inCodeBlock then
			output = output .. "-- " .. line .. "\n"
			if starts(line, "```lua") then inCodeBlock = true end
		end
	end
	return output
end

function litlua.install()
  table.insert(package.searchers, function(name)
    local dirsep = "/"
    local name_path = name:gsub("%.", dirsep)
    local file = nil
    for path in package.path:gmatch("[^;]+") do
      local file_path = path:gsub("?", name_path) .. ".md"
      file = io.open(file_path, 'r')
      if file then break end
    end

    if file then
      -- Read in the markdown source.
      local markdown = file:read("*a")
      file:close()

      -- Transform and load the module.
      local code = litlua.transform(markdown)
      res, err = loadstring(code, file_path)

      -- Return the module, or report an error.
      if not res then error(file_path .. ": " .. err) end
      return res
    else
      return nil, "Could not find .lua.md file"
    end
  end)
end

return litlua

main.lua

require("litlua").install()
require "primes"

primes.lua.md

First 100 Primes

Dumb example to demonstrate literate programming.

This quick example demonstrates how to write a Lua program that outputs the first 100 prime numbers. Let's start by defining a configurable variable that tells us how many primes to output.

local NUMBER_OF_PRIMES = 100 -- Change this to output more or less primes.

isPrime Helper Function

Now we'll create a helper function that can actually check if a number is prime.

function isPrime(num)
	if num < 2 then return false end
	if num == 2 then return true end
	for i=2,num - 1 do
		if num % i == 0 then return false end
	end
	return true
end

Printing Out The Primes

Finally, we can print out the prime numbers. We create two counters - one holding the number that we are checking (number) and one holding the number of primes that we have found so far (counter). We know that the first prime number is 2, so we start with number = 2.

local count, number = 0, 2
while count < NUMBER_OF_PRIMES do
	if isPrime(number) then
		print(number)
		count = count + 1
	end
	number = number + 1
end