As part of dobs, a C# CLI USD-VES converter, I wrote a library that provides the official exchange rate from the US dollar to Venezuelan Bolivars (VES). I developed the dobs app mainly for personal use and to practice building .NET applications in C#. I also took the opportunity to explore the CSharpFunctionalExtensions library. In this post, I describe this Rate Provider library, which can serve as an example use of CSharp Functional Extensions.

Going through the Rust track at exercism.org, I found the Nth Prime exercise. The exercise asks to determine the nth prime for a given integer n, considering 2 as the 0th prime. To make it more interesting, I decided to memoize the calculated primes in a table and to make the calculation thread-safe so that several primes can be computed concurrently. The implementation described here is available as a GitHub repo.

I assume the reader has some familiarity with monadic parsing in Haskell, particularly with the Attoparsec library, as well as with the diff formats parsed. For the latter, I invite you to read my previous article, where I described a grammar for diffs in these formats.

In this article, I describe a grammar for the normal and unified formats generated by the diff utility, and for the diff produced by git when comparing two files, which I’ll call git format. I describe the grammar in EBNF, as described on Wikipedia.

The first and second files being compared or diffed are usually called “original” and “new”, or “source” and “destination”. In this post, they are called left and right files.

In this article, you’ll learn to use optparse-applicative, an excellent Haskell library for parsing arguments for command-line programs. We will create a parser for an example app with several kinds of options, incrementally introducing the most commonly used library features.