ABSTRACT
Chapter 20 discusses the creation of domain specific languages. The combination of first-class environments, lexical scoping, and metaprogramming gives us a powerful toolkit for translating R code into other languages. One fully-fledged example of this idea is dbplyr, which powers the database backends for dplyr, allowing you to express data manipulation in R and automatically translate it into SQL. You can see the key idea in translate_sql() which takes R code and returns the equivalent SQL.
Translating R to SQL is complex because of the many idiosyncrasies of SQL dialects, so here I’ll develop two simple, but useful, domain specific languages (DSL): one to generate HTML, and the other to generate mathematical equations in LaTeX.
In “HTML” we create a DSL for generating HTML, using quasiquotation and purrr to generate a function for each HTML tag, then tidy evaluation to easily access them. In “LaTeX” we transform mathematically R code into its LaTeX equivalent using a combination of tidy evaluation and expression walking.
