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Tests 😀
CI 🥺

This library is a port of Django templates. Its coolest feature are:

  • template inheritance;
  • autoreload;
  • internationalization.

Also, there is nice documentation. In presence of documentation, I won't provide many examples. Instead, let's implement a small function for our HTML templating engines performance test.

I didn't find the way to load a template from the string. That is why we need to set up the library and let it know where to search template files:

POFTHEDAY> djula:*current-store*
#<DJULA:FILE-STORE {100248A8C3}>

POFTHEDAY> (djula:find-template djula:*current-store*
; Debugger entered on #<SIMPLE-ERROR "Template ~A not found" {1003D5F073}>
; Evaluation aborted on #<SIMPLE-ERROR "Template ~A not found" {1003D5F073}>

POFTHEDAY> (djula:add-template-directory "templates/")

Now we need to write such template to the templates/test.html:

<h1>{{ title }}</h1>
{% for item in items %}
  <li>{{ item }}</li>
{% endfor %}

And we can test it:

POFTHEDAY> (djula:find-template djula:*current-store*

(defparameter +welcome.html+ (djula:compile-template* "welcome.html"))

POFTHEDAY> (with-output-to-string (s)
             (djula:render-template* (djula:compile-template* "test.html")
                                     :title "Foo Bar"
                                     :items '("One" "Two" "Three")))
"<h1>Foo Bar</h1>





It is time to measure performance:

;; We need this to turn off autoreloading
;; and get good performance:
POFTHEDAY> (pushnew :djula-prod *features*)

POFTHEDAY> (defparameter *template*
             (djula:compile-template* "test.html"))

POFTHEDAY> (defun render (title items)
             (with-output-to-string (s)
               (djula:render-template* *template*
                                       :title title
                                       :items items)))

            (loop repeat 1000000
                  do (render "Foo Bar"
                             '("One" "Two" "Three"))))
Evaluation took:
  4.479 seconds of real time
  4.487983 seconds of total run time (4.453540 user, 0.034443 system)
  [ Run times consist of 0.183 seconds GC time, and 4.305 seconds non-GC time. ]
  100.20% CPU
  9,891,631,814 processor cycles
  1,392,011,008 bytes consed

Pay attention to the line adding :djula-prod to the *features*. It disables auto-reloading. Withf enabled auto-reloading rendering is 2 times slower and takes 10.6 microseconds.

I could recommend Djula to everybody who works in a team where HTML designers are writing templates and don't want to dive into Lisp editing.

With Djula they will be able to easily fix templates and see results without changing the backend's code.

More performance testing

Also, today I've decided to create a base-line function which will create HTML using string concatenation as fast as possible. This way we'll be able to compare different HTML templating engines with the hand-written code:

POFTHEDAY> (defun render-concat (title items)
             "This function does not do proper HTML escaping."
             (flet ((to-string (value)
                      (format nil "~A" value)))
               (apply #'concatenate
                      (append (list
                               (to-string title)
                              (loop for item in items
                                    collect "<li>"
                                    collect (to-string item)
                                    collect "</li>")

POFTHEDAY> (render-concat "Foo Bar"
                          '("One" "Two" "Three"))
"<title>Foo Bar</title><ul><li>One</li><li>Two</li><li>Three</li></ul>"

            (loop repeat 1000000
                  do (render-concat "Foo Bar"
                                    '("One" "Two" "Three"))))
Evaluation took:
  0.930 seconds of real time
  0.938568 seconds of total run time (0.919507 user, 0.019061 system)
  [ Run times consist of 0.114 seconds GC time, and 0.825 seconds non-GC time. ]
  100.97% CPU
  2,053,743,332 processor cycles
  864,022,384 bytes consed

Writing to stream a little bit slower, so we'll take as a base-line the result from render-concat:

POFTHEDAY> (defun render-stream (title items)
             "This function does not do proper HTML escaping."
             (flet ((to-string (value)
                      (format nil "~A" value)))
               (with-output-to-string (out)
                 (write-string "<title>" out)
                 (write-string (to-string title) out)
                 (write-string "</title><ul>" out)
                 (loop for item in items
                       do (write-string "<li>" out)
                          (write-string (to-string item) out)
                          (write-string "</li>" out))
                 (write-string "</ul>" out))))
            (loop repeat 1000000
                  do (render-stream "Foo Bar"
                                    '("One" "Two" "Three"))))
Evaluation took:
  1.208 seconds of real time
  1.214637 seconds of total run time (1.196847 user, 0.017790 system)
  [ Run times consist of 0.102 seconds GC time, and 1.113 seconds non-GC time. ]
  100.58% CPU
  2,667,477,282 processor cycles
  863,981,472 bytes consed

By, the way, I tried to use str:replace-all for escaping < and > symbols in the handwritten version of the render-concat function. But its performance degraded dramatically and became 36 microseconds.

str:replace-all uses cl-ppcre for text replacement.

What should I use instead?

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