run time error ! about purescript-native HOT 8 CLOSED

auto eqString() -> boxed {
    return Data_Eq::Eq()(Data_Eq::eqStringImpl());
};

FOREIGN_BEGIN( Data_String_Common )

//	split::Pattern->String->Array String

exports["split"] = [](const boxed& p_) -> boxed {
	return [=](const boxed& src_) -> boxed {
		const string& p = unbox<string>(p_);
		const string& s = unbox<string>(src_);

		size_t pos_start = 0, pos_end, delim_len = p.length();
		string token;
		array_t res;
		if (p.length() == 0 || s.length() == 0)
		{
			res.push_back(boxed(s));
			return res;
		}

		if (p.length() > 0 && s.length() > 0)
		{
			while ((pos_end = s.find(p, pos_start)) != string::npos) {
				token = s.substr(pos_start, pos_end - pos_start);
				pos_start = pos_end + delim_len;
				res.push_back(boxed(token));
			}

			res.push_back(boxed(s.substr(pos_start)));
		}
		return res;

	};
};
FOREIGN_END




FOREIGN_BEGIN(Data_String_CodePoints)
//foreign import _unsafeCodePointAt0
//:: (String->CodePoint)
//->String
//->CodePoint

exports["_unsafeCodePointAt0"] = [](const boxed& fallBack) -> boxed {

	return [=](const boxed & str) -> boxed {
		const string& s = unbox<string>(str);
		if (s.length() < 1)
		{
			return fallBack(str);
			//return fallBack(); this code also compile, which one I should use??
		}
		else
		{
			return s[0]; // the code is wrong , bcz chinese character takes 2 or more byte. 
		}
	};

};




exports["_toCodePointArray"] = [](const boxed& fallBack) -> boxed{

	return [=](const boxed & unsafeCodePointAt0) -> boxed {

		return [=](const boxed & str) -> boxed {

			const string& s = unbox<string>(str);
			if (s.length() < 1)
			{
				//printf("fall back\n");
				return fallBack(str);
			}
			else
			{
				array_t result;
			
				for (char c : s) {
					result.push_back(boxed(c));
				}
				return result;
			}
		};
	};

};


// -- Returns the first `n` characters of the string.
// foreign import take :: Int -> String -> String
exports["_take"] = [](const boxed& fallBack) -> boxed {
	return [=](const boxed& n_) -> boxed {
		return [=](const boxed& s_) -> boxed {
			const string& s = unbox<string>(s_);
			auto n = std::max(unbox<int>(n_), 0);
			auto l = s.size();
			return n >= l ? s : (n < 1 ? string("") : s.substr(0, n)); // the code is wrong , bcz chinese character takes 2 or more byte. 
		};
	};

};
FOREIGN_END

FOREIGN_BEGIN(Data_String_Unsafe)
//-- | Returns the character at the given index.
//-- |
//-- | **Unsafe:** throws runtime exception if the index is out of bounds.
//foreign import charAt::Int->String->Char


exports["charAt"] = [](const boxed& index_) -> boxed {
	return [=](const boxed& str_) -> boxed {
		const string& str = unbox<string>(str_);
		const int &  index = unbox<int>(index_);

		assert(str.length() >index && index >= 0);
		return str.substr(index, 1);;
	};
};
FOREIGN_END