Merge pull request #83 from fmichonneau/check-r-packages

generate_md_episodes <- function() {

    if (require("knitr")) {

        if (packageVersion("knitr") < '1.9.19') {

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

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

        }

    } else stop("knitr 1.9.20 or above is needed to build the lessons.")

    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)))