if (require("knitr") && packageVersion("knitr") < '1.9.19')

stop("knitr must be version 1.9.20 or higher")

if (!require("stringr"))

stop("The package stringr is required for generating the lessons.")

if (require("checkpoint")) {

required_pkgs <-

checkpoint:::projectScanPackages(project = "_episodes_rmd",

verbose=FALSE, use.knitr = TRUE)$pkgs

} else {

stop("The checkpoint package is required to build the lessons.")

}

missing_pkgs <- required_pkgs[!(required_pkgs %in% rownames(installed.packages()))]

if (length(missing_pkgs)) {

message("Installing missing required packages: ",

paste(missing_pkgs, collapse=", "))

install.packages(missing_pkgs)

}

## find all the Rmd files, and generates the paths for their respective outputs

src_rmd <- list.files(pattern = "??-*.Rmd$", path = "_episodes_rmd", full.names = TRUE)

dest_md <- file.path("_episodes", gsub("Rmd$", "md", basename(src_rmd)))

## knit the Rmd into markdown

mapply(function(x, y) {

knitr::knit(x, output = y)

}, src_rmd, dest_md)