Evaluate provides tools that allow you to recreate the parsing, evaluation and display of R code, with enough information that you can accurately recreate what happens at the command line. Evaluate + replay works very similarly to source(), but is written in such a way to make it easy to adapt for other output formats, such as html or latex.

There are three components to the evaluate package:

• parse_all, a version of parse that keeps expressions with their original source code, maintaining formatting and comments.
• evaluate, which evaluates each expression produced by parse_all, tracking all output, messages, warnings, and errors as their occur, and interleaving them in the correct order with the original source and value of the expression.
• replay, which outputs these pieces in a way that makes it look like you've entered the code at the command line. This function also serves as a template for other output formats.