Sometimes, when being interviewed for a job as a software developer, you’ll be asked a question such as “write a method that takes an integer as a parameter, and returns it’s factorial.”
For example, the factorial of 3 is represented as “3!”, which is calculated via 3*2*1, which equals 6. 4! is 4*3*2*1, which is 24, etc.
Putting aside whether these kinds of questions should be asked in an interview, if they’re asking you this, there’s a fairly high likelihood they’re asking for you to show that you understand recursion. If that’s the case, no problem, something like this will calculate the factorial:
let rec factorial n = match n with | 0 | 1 -> 1 | n when n > 0 && n <= 12 -> n * factorial (n - 1) | _ -> failwith "Parameter n is out of the supported range. Must be between 0 and 12."
This can be run in the F# interactive shell via:
> factorial 3;; val it : int = 6
But what if they want to find out whether you:
- Understand recursion, and…
- Know when you can avoid recursion, and just write simple methods instead.
When you want to visualize how a stock or portfolio has performed historically relative to the market as a whole, it is useful to create a comparison chart.
This article is written for the intermediate F# audience who has a basic familiarity of stock trading and technical analysis, and is intended to show the basics of implementing a backtesting system in F#.
If you’re an F# beginner it may not take too long for you to get up to speed on the concepts if you check out a few resources. In particular:
The backtesting strategy which you will implement is a simple SMA crossover where the fast line is 10 bars and the slow one 25. When the fast line crosses above the slow line, a buy signal will be triggered, and when the fast line cross below the slow line, a sell signal will be triggered. Only one long position will exist at any time, so the system will not trigger another buy order until after the long position is sold. Feel free to get in touch and send through any improvements, questions or corrections.