Happy Val....
forget it, it's just

val date : String = "14 February"

so Happy Immutable Variable day

I recommend book for who seeks to design a programming language:

- Programming Language Design Concepts by D. Watt, it suitable to understanding what a language needed to be called a programming language, it provided with comparison with real-world existing language.

- Programming Language Pragmatic by Michael Lee Scots. It focus on what the domain and the target of programming language, it more focused on what the target of your programming language and what needed for satisfy the domain target.

- Concept of Programming Language by Robert W. Sebesta, This book I suggested to read if you not want read the two book I had mentions. This book like what Watt's book but more refined, modern in material (it has Interview with language creator) and more baby step to read, this is book suitable if you like history class and surprise quiz in it.