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Low Entropy System for Templating

Lest is template engine/static site generator/whatever with low entropy and high customization. It removes unnecessary visual noise as <and > or end tags. Instead it uses efficient and rich Rebol syntax to describe the document. Custom plugins can be added very easily and basic distribution includes plugin for advanced Bootstrap support.


Lest describes HTML document in clutter-free way that is then translated to the mess that rules the world. See some examples (Lest source is prefixed with >> and HTML output with ==):

>> div "Hello World"
== <div>Hello World</div>

>> div #example "Hello World"
== <div id="example">Hello World"</div>

>> div #example .big .outline "Hello World"
== <div id="example" class="big outline">Hello World"</div>

>> div with [custom-tag: "custom value"] "Hello World"
== <div custom-tag="custom value">Hello World</div>

Ok, the last example is getting bit out of hand, so let's rewrite this using custom tags:

	custom: tempate [value] [div with [custom-tag: "custom value"] value]
	custom "Hello World"

	<div custom-tag="custom value">Hello World</div>	

Now we have this nonsense carried in custom tag, cleverly called CUSTOM, that accepts one parameter of STRING! datatype, called VALUE. So we can do this:

	custom: template [value] [div with [custom-tag: "custom value"] value]
	custom "Hello World" 
	custom "Hello completely unrelated World"

	<div custom-tag="custom value">Hello World</div>	
	<div custom-tag="custom value">Hello completely unrelated World</div>

Let's be fancy:

	custom: template [what who] [div [span .action what ", " span .name who "!"]]
	custom "Hello" "world"
	custom "Cheer up" "Brian"

	<div><span class="action">Hello</span>, <span class="name">world</span>!</div>
	<div><span class="action">Cheer up</span>, <span class="name">Brian</span>!</div>

These user templates can be used to construct complex layouts:

	user-post: template [name avatar title content] [
		div .user-post [
			div .user-info [
				div .user-name name
				img avatar
			div .message [
				h3 .post-title title
				p .post-content content

	user-post "Karel" "First Message" "Hello, this is my first message"
	user-post "Jana" "You are a Hero!" "I'm glad you've made it!"
	user-post "Bot" "Broadcast to all" "Please, don't polute this channel."

	<div class="user-post">
		<div class="user-info">
			<div class="user-name">Karel</div>
			<img src="">
		<div class="message">
			<h3 class="post-title">First Message</h3>
 			<p class="post-content">Hello, this is my first message</p>
 	<div class="user-post">
		<div class="user-info">
			<div class="user-name">Jana</div>
 			<img src="">
		<div class="message">
			<h3 class="post-title">You are a Hero!</h3>
 			<p class="post-content">I'm glad you've made it!</p>
	<div class="user-post">
		<div class="user-info">
			<div class="user-name">Bot</div>
			<img src="">
		<div class="message">
			<h3 class="post-title">Broadcast to all</h3>
			<p class="post-content">Please, don't polute this channel.</p>

So this is how you construct your templates, instead of repeating the same stuff over and over.

But this is still somehow static. So you can get the data from file or database:

... TODO: add example


Plugins are easy-to-write extensions that add more functionaliy than user rules. Lest come with plugins that add support for Bootstrap, different Google services (Maps, Analytics, Fonts, ...) and others.

	enable bootstrap 
	container [
		row [col 6 .upper "left column" col 6 .upper "right column"] 
		row [col 4 offset 4 .lower "middle column with 1/3 width"]

	<div class="container">
		<div class="row">
			<div class="upper col-md-6">
				<span>left column</span>
			<div class="upper col-md-6">
				<span>right column</span>
		<div class="row">
			<div class="lower col-md-4 col-md-offset-4">
				<span>middle column with 1/3 width</span>


Lest is written in Rebol language. You need Rebol 3 version to run Lest. It's not possible to run itunder Rebol 2. You can get latest Rebol binaries from or build a binary yourself from source at GitHub.

Example code


enable bootstrap
enable smooth-scrolling
enable google-font
stylesheet css-path/lest.css
google-font "Exo 2"
title "Hello world!"


navbar inverse 
    link active #basics "BASICS"
    link #code "DYNAMIC CODE"
    link #bootstrap "BOOTSTRAP SUPPORT"
    link #plugins "PLUGINS"

h1 #basics "Basic style support"
span "This is span."
div .my-style .my-other-style [
    div "Div in div"

h2 "Why Lest?"
li "fast"
li "small"
li "easy"

h1 #code "Dynamic page creation"

either (now/time < 12:00) "Good morning!" "Good afternoon"

my-custom-style: value string! [b [i value]]
my-custom-style "Hello world!"

h1 #bootstrap "Bootstrap support"

container [
    row #bootstrap [
        col offset 3 3 [ "Grid support" ]
        col 3 [ "Glyphicons:" glyphicon heart ]
        col 3 [ "Carousel, dropdown, modal..." ]

h1 #plugins "Plugins"

p {Lest supports different plugins:}

li "Google fonts"
li "Google maps"
li "Google analytics"
li "Font Awesome glyphs"
li "Captcha, etc..."

footer [ "more later" ]

Variables and user templates

You can set your words in Lest there are two types of them. User templates has been decribed above and are set using the set-word syntax.

Variables are words that hold one value and are set using SET syntax.

>> set value "Hello" span value
== <span>Hello</span>

Variables can also be used to change default settings like js-path or css-path.

Structural logic

In Lest, you are free to shoot yourself to foot using embeed Rebol code. However, Lest provides much safer basic structural logic that is preferred mode of operation. List of available commands follows.


IF is basic condition, dialect block is processed only if the condition is true.

>> if [now/time < 12:00][span "good morning"]
== <span>good morning</span>

>> if [now/time > 12:00][span "good morning"]
;; returns nothing

Condition is Rebol code or word of logic datatype.


EITHER is extened IF condition that accepts two values. In some languages this is achieved with crude IF ... THEN ... ELSE construct, Lest prefers much simpler EITHER

>> either [now/time < 12:00][span "good morning"][span "good evening"]
== <span>good morning</span>

One great feature of conditions and other structural logic in Lest is that it can be placed anywhere. So the above example can be simplified as:

>> span either [now/time < 12:00] "good morning" "good evening"
== <span>good morning</span>

>> span either [now/time < 12:00] .morning .evening "Hello!"
== <span class="morning">Hello!</span>

You get the idea.


SWITCH is multiple choice condition.

>> set x 1 span ["value is " switch x [1 "one" 2 "two" 3 "three"]]
== <span>value is one</span>

If the choice should return multiple elements, enclose it in block:

>> set x 2 span ["value is " switch x [1 "one" 2 [b "two"] 3 "three"]]
== <span>value is <b>two</b></span>

If the value is not in choices, Lest throws an error. Therefore it's wise to include the DEFAULT option:

>> set x 5 span ["value is " switch x [1 "one" 2 "two" 3 "three"] default "out of range"]
== "<span>value is out of range</span>"


FOR command takes block of values and applies a rule on each of them:

>> for planet in ["Earth" "Venus" "Mars"] [span planet]  
== <span>Earth</span><span>Venus</span><span>Mars</span>

The block can be of course referenced by name:

>> set planets ["Earth" "Venus" "Mars"] for planet in planets [span planet]
== <span>Earth</span><span>Venus</span><span>Mars</span>

Basic syntax is: FOR <word> IN <block> [...]

other structural logic

will be added later.


Low entropy HTML5 templating engine






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