Kaleidoscope parser made with LPeg

parser.lua

-- debug helper function
function _dump (t)
	local ttype = type(t)
	if ttype == "table" then
		local vals = {}
		for k,v in pairs(t) do
			table.insert(vals, _dump(k) .. " = " .. _dump(v))
		end
		return "{"..table.concat(vals, " , ").."}"
	elseif ttype == "string" then
		return string.format('%q', t)
	else
		return tostring(t)
	end
end
function dump(t) print(_dump(t)) end
function vdump(...)
	local t = {...}
	for k,v in pairs(t) do
		dump(v)
	end
end
--------------------------------
local lpeg = require"lpeg"

local R, S, V, P = lpeg.R, lpeg.S, lpeg.V, lpeg.P
local C, Ct, Cmt, Cg, Cb, Cc = lpeg.C, lpeg.Ct, lpeg.Cmt, lpeg.Cg, lpeg.Cb, lpeg.Cc
lpeg.locale(lpeg)
local digit, alnum, alpha, space, xdigit, punct = lpeg.digit, lpeg.alnum, lpeg.alpha, lpeg.space, lpeg.xdigit, lpeg.punct

local ws = (space^0)
local comment = P'#' * (1 - S"\r\n")^0 * S"\r\n"^1
ws = ws * comment^-1

--------------------------------
function sym(chars) return ws * P(chars) end

local keywords = {}
local function key(chars)
	keywords[chars] = true
	return ws * chars * -alnum
end

TokenTypes = {}
local function mark(name)
	TokenTypes[name] = true
	return function (...)
		return {name, ...}
	end
end
--------------------------------
local ident = ws * C( alpha * alnum ^ 0 ) * -alnum
ident = Cmt(ident, function(i, p, name)
	if keywords[name] then return false end
	return true, name
end) / mark"Ident"

local number = ws * C( digit ^ 1 * (P"." * digit^1)^-1 + digit ^ 0 * P"." * digit^1 ) * -alnum
number = number / mark"Number"

local op = ws * C(S"+/*-<>=:!?^$"^1) / mark"Operator"
local equals = sym"="
local comma = sym","

local arglist = (sym"(" *  (ident^0)  * sym")") / mark"ArgList"

local statement, ifstat, fn, fncall, extern, program = V"statement", V"ifstat", V"fn", V"fncall", V"extern", V"program"
local expr, exprlist, atom, forstat, vardecl, varstat = V"expr", V"exprlist", V"atom", V"forstat", V"vardecl", V"varstat"

local G = P{ program,
	program = (ws * (fn + extern + statement)^1 * ws * -1) / mark"Program";
	
	extern = (key"extern" * ident * arglist * sym";") / mark"ExternDecl";
	fn = (key"def" * ident * arglist * statement * sym";"^-1) / mark"Function";
	
	statement = (ifstat + forstat + expr) * sym";"^-1;
	ifstat = (key"if" * expr * key"then" * expr * key"else" * expr) / mark"IfStatement";
	forstat = (key"for" * ident * equals * expr * comma * expr * (comma * number)^-1 * key"in" * expr) / mark"ForStatement";
	
	exprlist = (sym"(" * ( expr * (sym"," * expr)^0 )^0 * sym")") / mark"ExprList" ;
	expr = ws * (atom * (op * atom)^0) / mark"Expr";
	atom = op^-1 * (fncall + number + ident);
	fncall = (ident * exprlist) / mark"FnCall";
}

--------------------------------

return G