git clone 'https://github.com/ruricolist/spinneret.git'
In the crowded space of Common Lisp HTML generators, SPINNERET occupies the following coordinates:
Modern. Targets HTML5. Does not treat XML and HTML as the same problem. Assumes you will be serving your documents as UTF-8.
Composable. Makes it easy to refactor HTML generation into separate functions and macros.
Pretty. Treats HTML as a document format, not a serialization. Output is idiomatic and readable, following the coding style of the HTML5 specification.
Aggressive. If something can be interpreted as HTML, then it will be, meaning that some Lisp forms can't be mixed with HTML syntax. In the trade-off between 90% convenience and 10% correctness SPINNERET is on the side of convenience.
Bilingual. Spinneret has the same semantics in Lisp and Parenscript.
HTML generation with SPINNERET looks like this:
(in-package #:spinneret) (defparameter *shopping-list* '("Atmospheric ponds" "Electric gumption socks" "Mrs. Leland's embyronic television combustion" "Savage gymnatic aggressors" "Pharmaceutical pianos" "Intravenous retribution champions")) (defparameter *user-name* "John Q. Lisper") (defparameter *last-login* "12th Never") (defmacro with-page ((&key title) &body body) `(with-html (:doctype) (:html (:head (:title ,title)) (:body ,@body)))) (defun shopping-list () (with-page (:title "Home page") (:header (:h1 "Home page")) (:section ("~A, here is *your* shopping list: " *user-name*) (:ol (dolist (item *shopping-list*) (:li (1+ (random 10)) item)))) (:footer ("Last login: ~A" *last-login*))))
<!DOCTYPE html> <html lang=en> <head> <meta charset=UTF-8> <title>Home page</title> </head> <body> <header> <h1>Home page</h1> </header> <section> John Q. Lisper, here is <em>your</em> shopping list: <ol> <li>10 Atmospheric ponds <li>6 Electric gumption socks <li>4 Mrs. Leland's embyronic television combustion <li>9 Savage gymnatic aggressors <li>6 Pharmaceutical pianos <li>9 Intravenous retribution champions </ol> </section> <footer> Last login: 12th Never </footer> </body> </html>
(Pretty-printing is pretty fast, but SPINNERET obeys
should you want to turn it off.)
The rules for WITH-HTML are these:
All generated forms write to
A keyword in function position is interpreted as a tag name. If the name is not valid as a tag, it is ignored.
Certain keywords are recognized as pseudo-tags and given special treatment:
:RAW :DOCTYPE :!DOCTYPE :CDATA :!– :COMMENT :HTML :HEAD
The value of the LANG attribute of HTML is controlled by
*html-lang*; the value of the meta charset attribute is controlled
Constant classes and ids can be specified with a selector-like syntax. E.g.:
(:div#wrapper (:div.section ...)) ≡ (:div :id "wrapper" (:div :class "section" ...))
Duplicate attributes are handled like duplicate keyword arguments: all values are evaluated, but only the leftmost value is used. The exception is the class attribute: the class of a tag is the union of all its :CLASS arguments.
The argument :DATASET introduces a list of :DATA-FOO arguments:
(:p :dataset (:duck (dolomphious) :fish 'fizzgigious :spoon "runcible")) ≡ (:p :data-duck (dolomphious) :data-fish 'fizzgigious :data-spoon "runcible")
For flexibility, even at the cost of efficiency, the argument :ATTRS introduces a form to evaluate at run time for a plist of extra attributes and values.
Forms after the attributes are treated as arguments. Each non-nil (primary) value returned by an argument to a tag is written to the stream by HTML, a generic function on which you can define your own methods. By default only literal arguments are printed. Literal arguments are strings, characters, numbers and symbols beside NIL.
A string in function position is first compiled as Markdown (using CL-MARKDOWN), then passed to FORMAT as a control string and applied to its arguments.
WITH-HTML-STRING is like WITH-HTML, but intercepts the generated HTML at run time and returns a string.
Sometimes it is useful for a piece of HTML-generating code to know
where in the document it appears. You might, for example, want to
tabulate that prints list-of-lists as rows of cells, but
only prints the surrounding
<table></table> if it is not already
within a table. The symbol
*HTML-PATH* holds a list of open tags, from
latest to earliest. Usually it will look something like
*html-path* ;-> '(:table :section :body :html)
Thus `tabulate' could be written
(defun tabulate (&rest rows) (with-html (flet ((tabulate () (loop for row in rows do (:tr (loop for cell in row do (:td cell)))))) (if (find :table *html-path*) (tabulate) (:table (:tbody (tabulate)))))))
The stumbling block for all sexp-based HTML generators is order of evaluation. It's tempting to write something like this:
;; Doesn't work (defun field (control) (with-html (:p control))) (defun input (default &key name label (type "text")) (with-html (:label :for name label) (:input :name name :id name :type type :value default)))
But it won't work: in
(field (input "Default" :name "why" :label
(input) gets evaluated before
(field), and the HTML
is printed inside-out.
Macros do work:
(defmacro field (control) `(with-html (:p ,control))) (defmacro input (name label &key (type "text")) `(with-html (:label :for ,name ,label) (:input :name ,name :id ,name :type ,type)))
But we can do better than this. Spinneret provides a macro-writing
deftag, which lets you refactor HTML without hiding it.
(deftag field (control attrs) `(:p ,@attrs ,@control)) (deftag input (default attrs &key name label (type "text")) (once-only (name) `(progn (:label :for ,name ,label) (:input :name ,name :id ,name :type ,type ,@attrs :value (progn ,@default)))))
A macro defined using
deftag takes its arguments just like an HTML
element. Instead of
(input "Default" :name "why" :label "Reason") ; defmacro
(input :name "why" :label "Reason" "Default") ; deftag
The macro re-arranges the arguments so they can be bound to an
ordinary lambda list, like the one above: the body of the tag is bound
to the first argument, and matching attributes are bound to keywords.
:dataset, and other shorthands are
handled exactly as in the usual HTML syntax.
But the great advantage of
deftag is how it handles attributes which
are not bound to keywords. In the definition of
deftag, you see that the
attrs catch-all argument is spliced into
the call to
:input. This means that any unhandled attributes pass
through to the actual input element.
(input :name "why" :label "Reason" :required t :class "special" "Default") => <label for=why>Reason</label> <input class=special name=why id=why type=text required value=Default>
input extends the
:input tag, almost like a subclass.
This is a very idiomatic and expressive way of building abstractions
(SPINNERET used to provide a more elaborate way of building HTML
deftag is simpler and more useful.)
The semantics of SPINNERET in Parenscript are almost the same. There
with-html returns a
Strings in function position are still parsed as Markdown, but
supplying arguments triggers an error (since Parenscript does not have
format). Templates and
*html-path* are not implemented for
SPINNERET does not do document validation, but it does warn, at compile time, about invalid tags and attributes.
Although HTML5 does include a mechanism for application-specific
data- prefix), some client-side frameworks choose to
employ their own prefixes instead. You can disable validation for a
given prefix by adding it to
(pushnew "ng-" *unvalidated-attribute-prefixes* :test #’equal)
Depends on TRIVIAL-GARBAGE, CL-MARKDOWN, PARENSCRIPT and ALEXANDRIA, which are Quicklisp-installable.