20.1 A bit of a recap

• Metaprogramming: To separate our description of the action from the action itself - Separate the code from its evaluation.
• Quasiquotation: combine code written by the function’s author with code written by the function’s user.
  • Unquotation: it gives the user the ability to evaluate parts of a quoted argument.
  • Evaluation: it gives the developer the ability to evluated quoted expression in custom environments.

Tidy evaluation: quasiquotation, quosures and data masks