Wrote a parser for a subset of canonical sexps

assets/.lua/csexp.lua

@@ -0,0 +1,66 @@
+local function _parse(str, init)
+	local pos = init
+	if string.find(str, "^%(", pos) then
+		pos = pos + 1
+		local list = {};
+		while true do
+			if string.find(str, "^%)", pos) then
+				pos = pos + 1
+				return list, pos
+			end
+			local child, new_pos = _parse(str, pos)
+			if not child then
+				error(string.format("expected ')', '(', or atom at index %d", pos))
+			end
+			table.insert(list, child)
+			pos = new_pos
+		end
+	else
+		local pos = init
+		local len_str = string.match(str, "^[1-9]%d*", pos)
+		if not len_str then
+			error(string.format("expected '(' or atom at index %d", pos))
+		end
+		local len = tonumber(len_str)
+		pos = pos+#len_str
+	
+		if not string.find(str, "^:", pos) then error(string.format("expected ':' at index %d", pos)) end
+		pos = pos + 1
+		local value = string.sub(str, pos, pos + len - 1)
+		if #value < len then error(string.format("unexpected end of string at index %d", pos)) end
+		pos = pos + len
+	
+		return value, pos
+	end
+end
+
+local function parse(str)
+	local value, pos = _parse(str, 1)
+	if pos <= #str then
+		error(string.format("extra characters at index %d", pos))
+	end
+	return value
+end
+
+local function _serialize(tokens, obj)
+	if type(obj) == "table" then
+		table.insert(tokens, "(")
+		for _, item in ipairs(obj) do
+			_serialize(tokens, item)
+		end
+		table.insert(tokens, ")")
+	else
+		local s = tostring(obj)
+		table.insert(tokens, tostring(#s))
+		table.insert(tokens, ":")
+		table.insert(tokens, s)
+	end
+end
+
+local function serialize(obj)
+	local tokens = {}
+	_serialize(tokens, obj)
+	return table.concat(tokens)
+end
+
+return {parse = parse, serialize = serialize}