Insert appropriate code chunk in emacs buffer

insert-code-chunk.el

(defun insert-md-code-chunk ()
  "Insert Rmd code chunk"
  (interactive)
  (insert "```\n\n```")
  (backward-char 4))

(defun insert-rmd-code-chunk ()
  "Insert Rmd code chunk"
  (interactive)
  (insert "```{r}\n\n```")
  (backward-char 4))

(defun insert-rnw-code-chunk ()
  "Insert Rnw code chunk"
  (interactive)
  (insert "<<>>=\n\n@")
  (backward-char 2))

(defun insert-org-code-chunk ()
  "Insert org code chunk"
  (interactive)
  (insert "#+BEGIN_SRC R :session *R*\n\n#+END_SRC")
  (backward-char 10))


(defun insert-code-chunk ()
  "Insert appropriate code chunk based on buffer extension"
  (interactive)
  (pcase (file-name-extension (buffer-file-name))
    (`"Rnw" (insert-rnw-code-chunk))
    (`"org" (insert-org-code-chunk))
    (`"Rmd" (insert-rmd-code-chunk)) 
    (`"md" (insert-md-code-chunk)) 
    (code (message "Unknown buffer extension"))))

(defun insert-el-code-chunk ()
"Insert emacs-lisp code chunk"
(interactive)
(insert "#+BEGIN_SRC emacs-lisp\n\n#+END_SRC")
(backward-char 10))