LearningElixir

After adding 16 new card brands, I’m finding the single file is getting slightly more complex than I’d like.

There’s only about 270 lines of code, but it’s difficult to come up with logical arrangement as many brands have multiple ranges in entirely different areas.

The first code runs nicely as a Livebook (v0.10.0) page. It recognizes American Express, Discover, Mastercard, and Visa payment card account numbers (PANs).

After being away from Elixir for a few weeks I thought it would take awhile to get back into the functional mindset, but I found it took less than an hour to start writing reasonable (I hope) code.

I’ve selected a small Elixir project to write between wrapping up one Python project and starting on the next. The SimpleCardBrand project will return the bank-card type based on the first six digits in the card.

A quick hex.pm search found packages that return more detailed information, but I didn’t find anything that ran without calling a web service.

I like this for a quick project as it can easily be done in a LiveBook and it primarily relies on function parameter pattern matching.

Let’s see where I am in a few days.

The Coding Gnome Elixir course is the most fun I’ve ever had with a programming course.

The course focuses primarily on how to structure an Elixir application. It explores isolating components into various agents and servers. Recommend you have at least some basic experience with Elixir before starting.

Creating a function that declares a parameter twice in order to check if two different passed-in parameters are identical is not something I would have thought of.

Drives home the point that pattern matching within a function is the same pattern matching used to select the function to run.

Notes

1. ?≠ returns a codepoint: 8800.

2. Dividing two integers returns a float. Use div and trunc to get integer results.

3. In Elixir, nil is false.

4. Regular expressions are based on PCRE (Perl lives on!).

5. =~ performs a regular expression match

   iex> str = "once upon a time"
   iex> str =~ ~r/u..n/
   true

6. =~ also accepts a string as its right hand argument, in which case it returns true if the left string contains the right.

7. Lists are not arrays. You cannot calculate an offset to a specific element.

8. map[:missingKey] returns nil. map.missingKey raises an exception.

I ran into the UTF-8 normalization issue when playing around with the String.split exercises.

Some non-ASCII values can be represented by either one or two graphemes. For example ô can be a single grapheme or composed of two graphemes, o and ^. Always working with normalized UTF-8 strings avoids confusion.

There are four types of UTF normalization which you can read about on the Unicode.org site. Elixir seems to prefer the Canonical Decomposition (NFD) form as that is what the String.equivalent? function uses.

The following examples demonstrate:

I had some confusion with the String.split function in yesterday’s exercises. The documentation says that the trim: true option removes empty strings from the resulting list.

The important term here is “empty”, not “blank” or “whitespace”. My Python-brain was still thinking of trim (or strip) options meaning whitespace is stripped from start/end of the source string.

For example:

Setting up the dictionary project as an actual separate Elixir project is a more structured approach than I’ve seen so far. Use of multiple projects has been previously discussed but examples to date have been more at the module level within a project. Excited to see this approach introduced so early in the course. Already changing my assumptions about future project construction.

Also new to me was the use of @ to run a function at compile time. I have used @ notation, but only to declare a fixed value. Not sure when I would use a dynamic compile-time value vs. a configuration, but good to know it exists.

Sticking with Dave Thomas for the moment and starting the Elixir for Programmers, Second Edition course. I’m expecting that much of this will be a refresher on what I’ve already covered, along with a first foray into Phoenix LiveView.

The LiveView will be a bit outdated given the recent major LiveView improvements, but mostly I’m looking for solid Elixir coding exercises.

I have a first project in mind, which does not require LiveView. Plan to start the project after I finish this course.