parsing sexps to lua (currently it works on single line)

parser.lua

function parse(file, start, len)
	local tree = {}
	local curcmd = '' -- currently parsed command
	local ix = start
	file:seek("set", ix)
	while(ix < len) do
		local r = file:read(1)
		ix = ix + 1
		if r then
			if r == "(" then
				local ta, dix = parse(file, ix, len)
				ix = dix
				file:seek("set", ix) -- jumps over body of lower scope
				table.insert(tree, ta)
			elseif r == ")" then
				if curcmd ~= '' then
					table.insert(tree, curcmd)
				end
				curcmd = ''
				break
			elseif r == " " then
				table.insert(tree, curcmd)
				curcmd = ''
			elseif r:match("%w") or (r == "#" and curcmd == '') then
				curcmd = curcmd .. r
			end
		end

	end
	return tree, ix
end

function bracket(str, spec)
	if spec then
		return spec .. str .. spec.reverse
	else
		if str:sub(0,1) == "#" then
			return '['..str:sub(2,str:len()-1)..']'
		else
			return '{'..str..'}'
		end
	end
end

function translate(tree)
	local buf = ''
	for i, v in ipairs(tree) do
		if type(v) == "table" then
			buf = buf .. bracket(translate(v))
		else
			if i ~= 1 then
				buf = buf .. bracket(v)
			else
				buf = buf .. '\\' .. v
			end
		end
	end

	return buf
end

function stripper(str)
	return str:sub(2,str:len()-1)
end

local filename = 'test.sexp'
local contents = io.open(filename, 'r')
local len = contents:seek("end")
local parsed, ex = parse(contents, 0, len)

print(stripper(translate(parsed)))

test.sexp

(frac 1 (die 6 #12))