From 926c4d89d08438984e91a8a02588283a18810b2c Mon Sep 17 00:00:00 2001
From: Francois Michonneau <francois.michonneau@gmail.com>
Date: Mon, 8 Jun 2015 12:08:20 -0400
Subject: [PATCH] check knitr version before converting Rmd to md

on a suggestion of @sritchie73 and @aammd
---
 Makefile                    | 3 ++-
 tools/check_knitr_version.R | 5 +++++
 2 files changed, 7 insertions(+), 1 deletion(-)
 create mode 100644 tools/check_knitr_version.R

diff --git a/Makefile b/Makefile
index b066465..f7da904 100644
--- a/Makefile
+++ b/Makefile
@@ -62,7 +62,8 @@ motivation.html : motivation.md _layouts/slides.revealjs Makefile
 	    -o $@ $<
 
 # Pattern to convert R Markdown to Markdown.
-%.md: %.Rmd $(R_CHUNK_OPTS)
+%.md: %.Rmd $(R_CHUNK_OPTS) tools/check_knitr_version.R
+	Rscript -e "source('tools/check_knitr_version.R')"
 	Rscript -e "knitr::knit('$$(basename $<)', output = '$$(basename $@)')"
 
 ## commands : Display available commands.
diff --git a/tools/check_knitr_version.R b/tools/check_knitr_version.R
new file mode 100644
index 0000000..ec6f94c
--- /dev/null
+++ b/tools/check_knitr_version.R
@@ -0,0 +1,5 @@
+if (require("knitr")) {
+    if (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.")
-- 
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