gistfile1.txt

// Daniel Z.'s solution
// Part 1.
// Implement a function prototype extension that caches function results for
// the same input arguments of a function with one parameter.
//
// For example:
// Make sin(1) have the result of Math.sin(1), but use a cached value
// for future calls.
//
// Part 2.
// Use this new function to refactor the code example.
// Some good test numbers: 524287, 9369319, 2147483647 (all primes)

function p(message){
	console.log(message)
}

Function.prototype.cached = function() { 
	if (!('cache' in this )){
		p("Setting up cache");
		this.cache = {}; 
	}
	if ( this.cache[ arguments[0] ] != null ) {
		p("From cache")
		return this.cache[ arguments[0] ]; 
	}
	else {
		return this.cache[arguments[0]] = arguments.callee.caller.compute(arguments[0])
	}
}

function isPrime( num ) { 
	if ( result = isPrime.cached(num) != null ) 
		return result; 
} 

isPrime.compute = function(num) { 
	p("From Computation")
	// everything but 1 can be prime
	var prime = num != 1;
	for ( var i = 2; i < num; i++ ) { 
		if ( num % i == 0 ) { 
			prime = false; 
			break; 
		} 
	} 
	return prime; 
}

p(isPrime(524287))
p(isPrime(524287))

p(isPrime(9369319))
p(isPrime(9369319))

p(isPrime(2147483647))
p(isPrime(2147483647))