hbomb79-query-parser.lua

local str = 'Test.wat#hi[a[1]=2] Child, Other'

local function clone(t, m)
	m = m or {}
	if m[t] then
		return m[t]
	elseif type(t) == 'table' then
		local r = {}
		m[t] = r
		for k, v in pairs(t) do
			r[clone(k, m)] = clone(v, m)
		end
		return r
	else
		return t
	end
end

local Tag = {
	type = nil;
	id = nil;
	classes = {};
	constraints = {};
	direct = false;
}

local query = {{clone(Tag)}}

while #str > 0 do
	print(('%q'):format(str))
	repeat
		local opt = query[#query]
		local tag = opt[#opt]

		local id, rest = str:match '^#([^%[%.#%s,]+)(.*)'
		if id then
			if tag.id then error('duplicate id at: ' .. ('%q'):format(str)) end
			tag.id, str = id, rest
			break
		end

		local class, rest = str:match '^%.([^%[%.#%s,]+)(.*)'
		if class then
			tag.classes[#tag.classes + 1], str = class, rest
			break
		end

		local typ, rest = str:match '^([^%[%.#%s,]+)(.*)'
		if typ then
			if tag.type then error('duplicate type at: ' .. ('%q'):format(str)) end
			tag.type, str = typ, rest
			break
		end

		local constraint, rest = str:match '^(%b[])(.*)'
		if constraint then
			tag.constraints[#tag.constraints + 1], str = constraint:sub(2, -2), rest
			break
		end

		local rest = str:match '^%s*>%s*(.*)'
		if rest then
			str = rest
			opt[#opt + 1] = clone(Tag)
			opt[#opt].direct = true
			break
		end

		local rest = str:match '^%s+(.+)'
		if rest then
			str = rest
			opt[#opt + 1] = clone(Tag)
			break
		end

		local rest = str:match '^%s*,%s*(.*)'
		if rest then
			str = rest
			query[#query + 1] = {clone(Tag)}
			break
		end

		error('unexpected at: ' .. ('%q'):format(str))
	until true
end

print(require'pl.pretty'.write(query))