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html->string (Super simple HTML templating for Lisp)
;; Copyright (c) 2020 Mark Polyakov
;; Released under the WTFPL (Do What The Fuck You Want To Public License)
(defvar *html-void-tags* '(:area :base :br :col :embed :hr :img :input :link
:meta :param :source :track :wbr)
"String designators for self-closing/void tags.
https://html.spec.whatwg.org/multipage/syntax.html#void-elements")
(defvar *html-escapes*
'(#\> ">"
#\< "&lt;"
#\& "&amp;"
#\" "&quot;"))
(defun escape (str)
(declare (string str))
(with-output-to-string (stream)
(loop for ch across str
for escaped = (getf *html-escapes* ch)
do (if escaped
(write-string escaped stream)
(write-char ch stream)))))
(defun html->string (html)
"The argument should be of the form (tag-name (attr-name attr-val) child1
child2 ...). Attributes and children are optional.
(html->string
'(html ()
(head ()
(title () \"My awesome website!\"))
(body ()
\"Hello! I'm Mark.\"
;; No attributes or children:
(br)
(a (href \"https://github.com/markasoftware\") \"My stuff\")
(br)
;; No children:
(img (src \"/cats.jpg\" alt \"My cute cats!\")))))
Since the argument must be quoted, you can use backquote notation to interleave
html and lisp:
`(div ()
\"My name is \"
,*my-name*
\", But you can call me:\"
(br)
(ul ()
,@(mapcar (lambda (name) `(li () ,name)) *my-nicknames*)))
All text and attribute values are escaped properly. You can use keyword symbols for tag and
attribute names if you'd like. There's a hardcoded list of self-closing tags, such as br and img.
Unescaped HTML can be inserted as a string using (:noescape \"<div>\"), for example. This is the
only time the second argument may be a string, so :noescape can still be used to designate
<noescape>."
(etypecase html
(null "")
(string (escape html))
(number (write-to-string html))
(cons
(cond
;; if html is not a valid html element, assume it's a list of html elements and recurse
((or (null (car html))
(not (symbolp (car html))))
(apply #'concatenate 'string (mapcar #'html->string html)))
((and (eq :noescape (car html))
(stringp (cadr html)))
(cadr html))
(t (destructuring-bind
;; the &key business forces an even number of arguments.
(tag &optional ((&rest attrs &key &allow-other-keys)) &rest body)
html
(check-type tag symbol)
;; printf is a child's toy. Honestly, regex might be too!
(format nil "<~A~:{ ~A=\"~A\"~}~:[/>~;>~A</~A>~]"
(string-downcase tag)
(loop for (attr-name attr-val) on attrs by #'cddr
collect
(list (string-downcase attr-name)
(escape (etypecase attr-val
((or string symbol) (string attr-val))
(number (write-to-string attr-val))))))
(not (member tag *html-void-tags* :test #'string=))
(apply #'concatenate 'string (mapcar #'html->string body))
(string-downcase tag))))))))
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