Wednesday, April 3, 2013

Interesting case for var -> val conversion in Scala

While Scala supports imperative as well as functional style of programming, it recommends programming in the latter. One of the challenges I faced was getting rid of a counter in the following BFS (Breadth First) style recursion (mutable to immutable variable conversion). I wont go into specifics but rather look at the pattern to be used here:

def BFSCounter(money: Int, coins: List[Int]): Int = {
    var n = 0
    // termination checks
    for (// loop dependent on input parameters
        n += BFSCounter( ...)
    n
}

The above code launches multiple recursions in each call of BFSCounter and the variable n which maintains the count must be incremented and returned.

The strategy to get rid of the mutable variable is to pass the counter from one call of BFSCounter to another. To do that we must also make the calls to BFSCounter a constant (independent of variables or input parameters). This means understanding the traversal pattern, termination checks etc. The final code looks like the following:

def BFSCounter2(money: Int, coins: List[Int]): Int = {
    // termination checks
    val count1 = BFSCounter2(...0..)
    BFSCounter2(count1)
}

Note that you may be able to reduce the code to just one call to BFSCounter2 or maybe you will need three calls. The point is that the number of calls should be finite and the counter is passed into the BFSCounter2 and passed back out as return value. The last call's return value is the final return value of the function.

About Tukeys

Tukeys provides consulting and software services to companies in healthcare and communications that are dealing with technical or scaling challenges. Please reach out to me on LinkedIn.

An interesting quite from John Tukey, who was an American mathematician (1915-2000) -

An approximate answer to the right problem is worth a good deal more than an exact answer to an approximate problem.

Today maths and statistics form the basis of how software is developed and used around us.

About Me

I have over 20 years of experience in healthcare, communications and AI.

I have a passion for defining innovative applications, creating product/technology strategy and solving challenging problems. My product mindset is helpful to any company to find patterns, reduce costs, and gain efficiencies.

I was the VP of Engineering at Vibrent Health, where I led the web, mobile, API and data products that supported one of the largest NIH programs - All of Us Research Program. Our system enrolled almost a million users and collected data from EHRs, surveys and wearables. Before that, I worked at hCentive, a pioneer in health exchanges.

As the CTO of 3CLogic, I helped create the first PC and web-only contact center solution that implemented PBX and CRM functionality as an affordable SaaS solution. As the Chief Architect of NexTone, I was instrumental in the development of SIP and SIP based products. SIP and associated protocols form the basis of modern WebRTC APIs.

If you are a growth company or invest in growing companies that are facing technical or scaling challenges, I can be a tremendous help. Contact me on LinkedIn.