Write the Code You Want

“Write the code you want and then make it compile” was a thought expressed on library design while I was at the NE Scala Symposium. It is a different way to describe the TDD maxim of letting the usage in tests guide the design. It is very much influenced by the extremely flexible syntax rules and DSL creation abilities in Scala. One of the talks, Can a DSL be Human? by Katrin Shechtman, took a song’s lyrics and produced a DSL that would compile them.

Since you can make any set of arbitrary semantics compile, there is no reason you can’t have the code you want for your application. There is an underlying library layer that may not be the prettiest code, or may be significantly verbose but you can always make it work. Segregating the complexity to one portion of the code base means that most of the business logic is set up in a clean fashion and that the related errors can be handled in a structured and centralized fashion.

Taking the time to do all of this for a little utility probably isn’t worth it, but the more often a library is used the more valuable this becomes. If you’ve got a library that will be used by hundreds, really refining the interface to make it match how you think would be really user friendly.

Building software that works is the easy part, building an intuitive interface and all of the comprehensive documentation so others can understand what a library can do for you is the hard part. I’m going to take this to heart with some changes coming up with a library at work.

This still doesn’t even cover the aspect of deciding what you want. There are different ways you can express the same idea. The difference between a function, a symbolic operator, or create a DSL can all express the same functionality. You can express the domain in multiple ways, case classes, enums, or a sealed trait. You can declare a trait, a free function, or an implicit class. Deciding on the right way to express all of this is the dividing line between a working library and a good library.


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