parseFile.lua2p

--[[============================================================
--=
--=  LuaPreprocess example: Pre-parse a data file.
--=
--=  Here we convert a JSON data string to a more appropriate
--=  data format in the metaprogram. The final program will not
--=  contain anything related to JSON - just a nice Lua table
--=  literal with all data.
--=
--============================================================]]

-- Metaprogram.
--==============================================================

!(
function eatWhitespace(str, pos)
	local i1, i2 = str:find("^%s*", pos)
	pos = i2+1
	return pos
end

function parseNumber(json, pos)
	-- We only support positive integers for now.
	local i1, i2, n = json:find("^(%d+)", pos)

	n   = tonumber(n)
	pos = i2+1

	return n, pos
end

function parseString(json, pos)
	-- We assume strings don't contain escape sequences.
	local i1, i2, s = json:find('^"(.-)"', pos)

	if not s then
		error("Invalid string: "..json:sub(pos))
	end

	pos = i2+1

	return s, pos
end

function parseArray(json, pos)
	pos = pos+1 -- Eat the initial '['.

	local array = {}

	for i = 1, math.huge do
		pos = eatWhitespace(json, pos)

		local char = json:sub(pos, pos)

		if char == "" then
			error("Unexpected end of array: "..json:sub(pos))
		elseif char == "]" then
			pos = pos+1 -- Eat the ']'.
			break
		end

		-- Ensure there's a comma between items.
		if i > 1 then
			if char == "," then
				pos = pos+1 -- Eat the ','.
				pos = eatWhitespace(json, pos)
			else
				error("Expected a comma: "..json:sub(pos))
			end
		end

		local item
		item, pos = parseJson(json, pos)
		array[i] = item
	end

	return array, pos
end

function parseObject(json, pos)
	pos = pos+1 -- Eat the initial '{'.

	local object = {}

	for i = 1, math.huge do
		pos = eatWhitespace(json, pos)

		local char = json:sub(pos, pos)

		if char == "" then
			error("Unexpected end of object: "..json:sub(pos))
		elseif char == "}" then
			pos = pos+1 -- Eat the '}'.
			break
		end

		-- Ensure there's a comma between items.
		if i > 1 then
			if char == "," then
				pos  = pos+1 -- Eat the ','.
				pos  = eatWhitespace(json, pos)
				char = json:sub(pos, pos)

			else
				error("Expected a comma: "..json:sub(pos))
			end
		end

		if char ~= '"' then
			error("Invalid key: "..json:sub(pos))
		end

		local key
		key, pos = parseString(json, pos)

		pos  = eatWhitespace(json, pos)
		char = json:sub(pos, pos)

		if char == ":" then
			pos = pos+1 -- Eat the ':'.
			pos = eatWhitespace(json, pos)
		else
			error("Expected a colon: "..json:sub(pos))
		end

		local value
		value, pos = parseJson(json, pos)

		object[key] = value
	end

	return object, pos
end

function parseJson(json, pos)
	pos = pos or 1
	pos = eatWhitespace(json, pos)

	local char = json:sub(pos, pos)

	if char == '"' then
		return parseString(json, pos)
	elseif char == "[" then
		return parseArray(json, pos)
	elseif char == "{" then
		return parseObject(json, pos)
	elseif char:find"^%d" then
		return parseNumber(json, pos)
	else
		error("Unexpected character: "..json:sub(pos))
	end
end

local json = [[
{
	"characters": [
		{
			"id":   1,
			"name": "Warrior",
			"type": "melee",
			"actions": [
				{"slot":"left",  "title":"Slash"},
				{"slot":"right", "title":"Block"}
			]
		},
		{
			"id":   2,
			"name": "Spell Caster",
			"type": "magic",
			"actions": [
				{"slot":"left",     "title":"Fireball"},
				{"slot":"right",    "title":"Illuminate"},
				{"slot":"familiar", "title":"Swoop"}
			]
		}
	]
}
]]

local data = parseJson(json)
)

-- The program.
--==============================================================

local characters = !(data.characters)

function printAvailableCharacters()
	print("Available characters:")

	for i, character in ipairs(characters) do
		print(string.format(
			"%d. %s (type: %s, actions: x%d)",
			i,
			character.name,
			character.type,
			#character.actions
		))
	end
end

printAvailableCharacters()

--==============================================================