Exercises in Programming Style–Infinite Mirror

NOTE : read the rest of the series, or check out the source code.

If you enjoy read­ing these exer­cises then please buy Crista’s book to sup­port her work.

exercises-prog-styles-cover

Fol­low­ing on from the last post, we will look at the Infinite Mirror style today.

 

Style 7 – Infinite Mirror

This style is really all about recursions.

Constraints

  • All, or a significant part, of the problem is modelled using induction.

 

First, let’s get the list of stop words and put them in a set:

image

and then we will implement the counting logic using recursion:

image

I made some adjustments to Crista’s version here. In her version, wordFreqs is a global state that has been passed in as argument but the recursive count function returns nothing.

In my implementation, although I’m still using a mutable dictionary, it’s an implementation detail that is not exposed to the outside world. I could have used a Map here instead, but constantly updating a Map is really clumsy, plus Map performs really poorly in this type of use pattern.

 

Then we have another recursive functions, for printing out the word frequencies:

image

and then some code to tie everything together:

image

 

You can find all the source code for this exer­cise here.

Enjoy what you’re reading? Subscribe to my newsletter and get more content on AWS and serverless technologies delivered straight to your inbox.


Yan Cui

I’m an AWS Serverless Hero and the author of Production-Ready Serverless. I have run production workload at scale in AWS for nearly 10 years and I have been an architect or principal engineer with a variety of industries ranging from banking, e-commerce, sports streaming to mobile gaming. I currently work as an independent consultant focused on AWS and serverless.

You can contact me via Email, Twitter and LinkedIn.

Hire me.


Check out my new course, Complete Guide to AWS Step Functions.

In this course, we’ll cover everything you need to know to use AWS Step Functions service effectively. Including basic concepts, HTTP and event triggers, activities, design patterns and best practices.

Get Your Copy