R has had this since at least 2000. The man pages for each function contain an "examples" block, and these are expected (but don't need) to be executable. They

R has had this since at least 2000. The man pages for each function contain an "examples" block, and these are expected (but don't need) to be executable. They then took it a step further a couple of years later going down the literate programming path with SWeave, and later Rmd.