toHtml ((Heading n d):xs) = "\n<h"++show n++">"++toHtml d++"</h"++show n++">\n"++toHtml xs
toHtml ((Url l):xs) = "<link: "++l++">"++toHtml xs
toHtml ((Pre s):xs) = "<pre>"++s++"</pre>"++toHtml xs
toHtml ((Heading n d):xs) = "\n<h"++show n++">"++toHtml d++"</h"++show n++">\n"++toHtml xs
toHtml ((Url l):xs) = "<link: "++l++">"++toHtml xs
toHtml ((Pre s):xs) = "<pre>"++s++"</pre>"++toHtml xs