typed.js

// when applied, this function should check each of the items in s against the input arguments,
// and the result to r
// when the original is applied, this will simply return the input if valid, or throw if invalid
// for higher-order functions
// the function is not yet evaluated, but we pass a validator and wrap the function
// this will be inspected when provided function is called

const func = (s,r) => fn => {
	const f = (...args) => {
		const ret = fn(...args.map((a,i) => {
			const t = s[i](a);
			if(typeof t == "function" && t.hasOwnProperty("__wraps")) {
				if(t.__wraps !== a) throw new Error("unknown function found");
			} else {
				if(t !== a) throw new Error("incorrect input type");
			}
			return t;
		}));
		if(r(ret) !== ret) throw new Error("incorrect output type");
		return ret;
	};
	f.__wraps = fn;
	return f;
};

// array test
const array = (a) => !Array.isArray(a) || a;

var add = (a,b) => a + b;
var addOne = add.bind(null,1);
var map = (a,f) => a.map(x => f(x));

var typed = func([array,func([Number],Number)],array);

// apply function with test (should fail):
typed(map)(["1",2,3],addOne);