In lbartnik/chronicler: Binary History for R

library(knitr)
library(utilities)

knitr::opts_chunk$set(collapse = TRUE, comment = NA, prompt = FALSE, echo = TRUE)

options(crayon.enabled = TRUE)
knitr::knit_hooks$set(output = utilities::ansi_handler)
knitr::knit_hooks$set(message = utilities::ansi_handler)

# try old.hooks <- set_knit_hooks(knitr::knit_hooks)

original_output_hook <- knit_hooks$get("output")
knit_hooks$set(output = utilities::create_trimming_hook(original_output_hook))

options(chronicler.attach = FALSE)
library(chronicler)

The R snippet below adds a new engine to knitr. In knitr, an engine is a mechanism of handling a code chunk in language other than R. In our case, we add a very simple chronicler engine. From now on, each code chunk marked as {chronicler} will be passed to the new engine.

knitr::knit_engines$set(chronicler = function (options) {
  id <- as.character(options$code)
  stopifnot(is_artifact_id(id))

  knitted <- knit_artifact(id)
  engine_output(options, id, knitted$out, knitted$extra)
})

Let's see what exactly does it do. First, it casts the chunk's code as a string (as.character) and immediately checks if it matches the definition of an artifact identifier; if not, an exception is thrown. Then it passes control to chronicler::knit_artifact whose output is finally passed to knitr::engine_output. So what it is that knit_artifact does?

It's actually pretty straightforward. It calls the default print method for the "artifact" class and captures its output into a HTML snippet. This is the result box which immediately follows the long string -- our artifact identifier.

The second thing that knit_artifact does is capturing the sequence of R commands that resulted in the requested artifact. It formats and syntax-highlights each of these commands, and then puts them in another HTML box. This additional result box that is hidden by default and can be displayed by clicking on the explain artifact 57f... link. To hide the extended explanation just click on the link once again.

chronicler:::attach_to_repository(london_meters())

57fbe7553e11c7b0149040f5781c209b266ed637

lbartnik/chronicler documentation built on May 23, 2019, 8:21 p.m.