popsu-d7/sites/all/libraries/lessphp/docs/docs.md

title: v0.3.8 documentation
link_to_home: true

--

Documentation v0.3.8

$index

lessphp is a compiler that generates CSS from a superset language which adds a collection of convenient features often seen in other languages. All CSS is compatible with LESS, so you can start using new features with your existing CSS.

It is designed to be compatible with less.js, and suitable as a drop in replacement for PHP projects.

Getting Started

The homepage for lessphp can be found at http://leafo.net/lessphp/.

You can follow development at the project's GitHub.

Including lessphp in your project is as simple as dropping the single include file into your code base and running the appropriate compile method as described in the PHP Interface.

Installation

lessphp is distributed entirely in a single stand-alone file. Download the latest version from either the homepage or GitHub.

Development versions can also be downloading from GitHub.

Place lessphp.inc.php in a location available to your PHP scripts, and include it. That's it! you're ready to begin.

The Language

lessphp is very easy to learn because it generally functions how you would expect it to. If you feel something is challenging or missing, feel free to open an issue on the bug tracker.

It is also easy to learn because any standards-compliant CSS code is valid LESS code. You are free to gradually enhance your existing CSS code base with LESS features without having to worry about rewriting anything.

The following is a description of the new languages features provided by LESS.

Line Comments

Simple but very useful; line comments are started with //:

```less
// this is a comment
body {
  color: red; // as is this
  /* block comments still work also */
}
```

Variables

Variables are identified with a name that starts with @. To declare a variable, you create an appropriately named CSS property and assign it a value:

```less
@family: "verdana";
@color: red;
body {
  @mycolor: red;
  font-family: @family;
  color: @color;
  border-bottom: 1px solid @color;
}
```

Variable declarations will not appear in the output. Variables can be declared in the outer most scope of the file, or anywhere else a CSS property may appear. They can hold any CSS property value.

Variables are only visible for use from their current scope, or any enclosed scopes.

If you have a string or keyword in a variable, you can reference another variable by that name by repeating the @:

```less
@value: 20px;
@value_name: "value";

width: @@value_name;
```

Expressions

Expressions let you combine values and variables in meaningful ways. For example you can add to a color to make it a different shade. Or divide up the width of your layout logically. You can even concatenate strings.

Use the mathematical operators to evaluate an expression:

```less
@width: 960px;
.nav {
  width: @width / 3;
  color: #001 + #abc;
}
.body {
  width: 2 * @width / 3;
  font-family: "hel" + "vetica";
}
```

Parentheses can be used to control the order of evaluation. They can also be used to force an evaluation for cases where CSS's syntax makes the expression ambiguous.

The following property will produce two numbers, instead of doing the subtraction:

```less
margin: 10px -5px;
```

To force the subtraction:

```less
margin: (10px -5px);
```

It is also safe to surround mathematical operators by spaces to ensure that they are evaluated:

```less
margin: 10px - 5px;
```

Division has a special quirk. There are certain CSS properties that use the / operator as part of their value's syntax. Namely, the font shorthand and border-radius.

Thus, lessphp will ignore any division in these properties unless it is wrapped in parentheses. For example, no division will take place here:

```less
.font {
  font: 20px/80px "Times New Roman";
}
```

In order to force division we must wrap the expression in parentheses:

```less
.font {
  font: (20px/80px) "Times New Roman";
}
```

If you want to write a literal / expression without dividing in another property (or a variable), you can use string unquoting:

```less
.var {
  @size: ~"20px/80px";
  font: @size sans-serif;
}
```

Nested Blocks

By nesting blocks we can build up a chain of CSS selectors through scope instead of repeating them. In addition to reducing repetition, this also helps logically organize the structure of our CSS.

```less
ol.list {
  li.special {
    border: 1px solid red;
  }

  li.plain {
    font-weight: bold;
  }
}
```

This will produce two blocks, a ol.list li.special and ol.list li.plain.

Blocks can be nested as deep as required in order to build a hierarchy of relationships.

The & operator can be used in a selector to represent its parent's selector. If the & operator is used, then the default action of appending the parent to the front of the child selector separated by space is not performed.

```less
b {
  a & {
    color: red;
  }

  // the following have the same effect

  & i {
    color: blue;
  }

  i {
    color: blue;
  }
}
```

Because the & operator respects the whitespace around it, we can use it to control how the child blocks are joined. Consider the differences between the following:

```less
div {
  .child-class { color: purple; }

  &.isa-class { color: green; }

  #child-id { height: 200px; }

  &#div-id { height: 400px; }

  &:hover { color: red; }

  :link { color: blue; }
}
```

The & operator also works with mixins, which produces interesting results:

```less
.within_box_style() {
  .box & {
    color: blue;
  }
}

#menu {
  .within_box_style;
}
```

Mixins

Any block can be mixed in just by naming it:

```less
.mymixin {
  color: blue;
  border: 1px solid red;

  .special {
    font-weight: bold;
  }
}


h1 {
  font-size: 200px;
  .mixin;
}
```

All properties and child blocks are mixed in.

Mixins can be made parametric, meaning they can take arguments, in order to enhance their utility. A parametric mixin all by itself is not outputted when compiled. Its properties will only appear when mixed into another block.

The canonical example is to create a rounded corners mixin that works across browsers:

```less
.rounded-corners(@radius: 5px) {
  border-radius: @radius;
  -webkit-border-radius: @radius;
  -moz-border-radius: @radius;
}

.header {
  .rounded-corners();
}

.info {
  background: red;
  .rounded-corners(14px);
}
```

If you have a mixin that doesn't have any arguments, but you don't want it to show up in the output, give it a blank argument list:

```less
.secret() {
  font-size: 6000px;
}

.div {
  .secret;
}
```

If the mixin doesn't need any arguments, you can leave off the parentheses when mixing it in, as seen above.

You can also mixin a block that is nested inside other blocks. You can think of the outer block as a way of making a scope for your mixins. You just list the names of the mixins separated by spaces, which describes the path to the mixin you want to include. Optionally you can separate them by >.

```less
.my_scope  {
  .some_color {
    color: red;
    .inner_block {
      text-decoration: underline;
    }
  }
  .bold {
    font-weight: bold;
    color: blue;
  }
}

.a_block {
  .my_scope .some_color;
  .my_scope .some_color .inner_block;
}

.another_block {
  // the alternative syntax
  .my_scope > .bold;
}
```

@arguments Variable

Within an mixin there is a special variable named @arguments that contains all the arguments passed to the mixin along with any remaining arguments that have default values. The value of the variable has all the values separated by spaces.

This useful for quickly assigning all the arguments:

```less
.box-shadow(@x, @y, @blur, @color) {
  box-shadow: @arguments;
  -webkit-box-shadow: @arguments;
  -moz-box-shadow: @arguments;
}
.menu {
  .box-shadow(1px, 1px, 5px, #aaa);
}
```

In addition to the arguments passed to the mixin, @arguments will also include remaining default values assigned by the mixin:

```less
.border-mixin(@width, @style: solid, @color: black) {
  border: @arguments;
}

pre {
  .border-mixin(4px, dotted);
}

```

Pattern Matching

When you mix in a mixin, all the available mixins of that name in the current scope are checked to see if they match based on what was passed to the mixin and how it was declared.

The simplest case is matching by number of arguments. Only the mixins that match the number of arguments passed in are used.

```less
.simple() { // matches no arguments
  height: 10px;
}

.simple(@a, @b) { // matches two arguments
  color: red;
}

.simple(@a) { // matches one argument
  color: blue;
}

div {
  .simple(10);
}

span {
  .simple(10, 20);
}
```

Whether an argument has default values is also taken into account when matching based on number of arguments:

```less
// matches one or two arguments
.hello(@a, @b: blue) {
  height: @a;
  color: @b;
}

.hello(@a, @b) { // matches only two
  width: @a;
  border-color: @b;
}

.hello(@a) { // matches only one
  padding: 1em;
}

div {
  .hello(10px);
}

pre {
  .hello(10px, yellow);
}
```

Additionally, a vararg value can be used to further control how things are matched. A mixin's argument list can optionally end in the special argument named .... The ... may match any number of arguments, including 0.

```less
// this will match any number of arguments
.first(...) {
  color: blue;
}

// matches at least 1 argument
.second(@arg, ...) {
  height: 200px + @arg;
}

div { .first("some", "args"); }
pre { .second(10px); }
```

If you want to capture the values that get captured by the vararg you can give it a variable name by putting it directly before the .... This variable must be the last argument defined. It's value is just like the special @arguments variable, a space separated list.

```less
.hello(@first, @rest...) {
  color: @first;
  text-shadow: @rest;
}

span {
  .hello(red, 1px, 1px, 0px, white);
}

```

Another way of controlling whether a mixin matches is by specifying a value in place of an argument name when declaring the mixin:

```less
.style(old, @size) {
  font: @size serif;
}

.style(new, @size) {
  font: @size sans-serif;
}

.style(@_, @size) {
  letter-spacing: floor(@size / 6px);
}

em {
  @switch: old;
  .style(@switch, 15px);
}
```

Notice that two of the three mixins were matched. The mixin with a matching first argument, and the generic mixin that matches two arguments. It's common to use @_ as the name of a variable we intend to not use. It has no special meaning to LESS, just to the reader of the code.

Guards

Another way of restricting when a mixin is mixed in is by using guards. A guard is a special expression that is associated with a mixin declaration that is evaluated during the mixin process. It must evaluate to true before the mixin can be used.

We use the when keyword to begin describing a list of guard expressions.

Here's a simple example:

```less
.guarded(@arg) when (@arg = hello) {
  color: blue;
}

div {
  .guarded(hello); // match
}

span {
  .guarded(world); // no match
}
```

Only the div's mixin will match in this case, because the guard expression requires that @arg is equal to hello.

We can include many different guard expressions by separating them by commas. Only one of them needs to match to trigger the mixin:

```less
.x(@a, @b) when (@a = hello), (@b = world) {
  width: 960px;
}

div {
  .x(hello, bar); // match
}

span {
  .x(foo, world); // match
}

pre {
  .x(foo, bar); // no match
}
```

Instead of a comma, we can use and keyword to make it so all of the guards must match in order to trigger the mixin. and has higher precedence than the comma.

```less
.y(@a, @b) when (@a = hello) and (@b = world) {
  height: 600px;
}

div {
  .y(hello, world); // match
}

span {
  .y(hello, bar); // no match
}
```

Commas and ands can be mixed and matched.

You can also negate a guard expression by using not in from of the parentheses:

```less
.x(@a) when not (@a = hello) {
  color: blue;
}

div {
  .x(hello); // no match
}
```

The = operator is used to check equality between any two values. For numbers the following comparison operators are also defined:

<, >, =<, >=

There is also a collection of predicate functions that can be used to test the type of a value.

These are isnumber, iscolor, iskeyword, isstring, ispixel, ispercentage and isem.

```less
.mix(@a) when (ispercentage(@a)) {
  height: 500px * @a;
}
.mix(@a) when (ispixel(@a)) {
  height: @a;
}

div.a {
  .mix(50%);
}

div.a {
  .mix(350px);
}
```

!important

If you want to apply the !important suffix to every property when mixing in a mixin, just append !important to the end of the call to the mixin:

```less
.make_bright {
  color: red;
  font-weight: bold;
}

.color {
  color: green;
}

body {
  .make_bright() !important;
  .color();
}

```

Selector Expressions

Sometimes we want to dynamically generate the selector of a block based on some variable or expression. We can do this by using selector expressions. Selector expressions are CSS selectors that are evaluated in the current scope before being written out.

A simple example is a mixin that dynamically creates a selector named after the mixin's argument:

```less
.create-selector(@name) {
  (e(@name)) {
    color: red;
  }
}

.create-selector("hello");
.create-selector("world");
```

Any selector that is enclosed in () will have it's contents evaluated and directly written to output. The value is not changed any way before being outputted, thats why we use the e function. If you're not familiar, the e function strips quotes off a string value. If we didn't have it, then the selector would have quotes around it, and that's not valid CSS!

Any value can be used in a selector expression, but it works best when using strings and things like String Interpolation.

Here's an interesting example adapted from Twitter Bootstrap. A couple advanced things are going on. We are using Guards along with a recursive mixin to work like a loop to generate a series of CSS blocks.

```less
// create our recursive mixin:
.spanX (@index) when (@index > 0) {
  (~".span@{index}") {
    width: @index * 100px;
  }
  .spanX(@index - 1);
}
.spanX (0) {}

// mix it into the global scopee:
.spanX(4);
```

Import

Multiple LESS files can be compiled into a single CSS file by using the @import statement. Be careful, the LESS import statement shares syntax with the CSS import statement. If the file being imported ends in a .less extension, or no extension, then it is treated as a LESS import. Otherwise it is left alone and outputted directly:

```less
// my_file.less
.some-mixin(@height) {
  height: @height;
}

// main.less
@import "main.less" // will import the file if it can be found
@import "main.css" // will be left alone

body {
  .some-mixin(400px);
}
```

All of the following lines are valid ways to import the same file:

```less
@import "file";
@import 'file.less';
@import url("file");
@import url('file');
@import url(file);
```

When importing, the importDir is searched for files. This can be configured, see PHP Interface.

String Interpolation

String interpolation is a convenient way to insert the value of a variable right into a string literal. Given some variable named @var_name, you just need to write it as @{var_name} from within the string to have its value inserted:

```less
@symbol: ">";
h1:before {
  content: "@{symbol}: ";
}

h2:before {
  content: "@{symbol}@{symbol}: ";
}
```

There are two kinds of strings, implicit and explicit strings. Explicit strings are wrapped by double quotes, "hello I am a string", or single quotes 'I am another string'. Implicit strings only appear when using url(). The text between the parentheses is considered a string and thus string interpolation is possible:

```less
@path: "files/";
body {
  background: url(@{path}my_background.png);
}
```

String Format Function

The % function can be used to insert values into strings using a format string. It works similar to printf seen in other languages. It has the same purpose as string interpolation above, but gives explicit control over the output format.

```less
@symbol: ">";
h1:before {
  content: %("%s: ", @symbol);
}
```

The % function takes as its first argument the format string, following any number of addition arguments that are inserted in place of the format directives.

A format directive starts with a % and is followed by a single character that is either a, d, or s:

```less
strings: %("%a %d %s %a", hi, 1, 'ok', 'cool');
```

%a and %d format the value the same way: they compile the argument to its CSS value and insert it directly. When used with a string, the quotes are included in the output. This typically isn't what we want, so we have the %s format directive which strips quotes from strings before inserting them.

The %d directive functions the same as %a, but is typically used for numbers assuming the output format of numbers might change in the future.

String Unquoting

Sometimes you will need to write proprietary CSS syntax that is unable to be parsed. As a workaround you can place the code into a string and unquote it. Unquoting is the process of outputting a string without its surrounding quotes. There are two ways to unquote a string.

The ~ operator in front of a string will unquote that string:

```less
.class {
  // a made up, but problematic vendor specific CSS
  filter: ~"Microsoft.AlphaImage(src='image.png')";
}
```

If you are working with other types, such as variables, there is a built in function that let's you unquote any value. It is called e.

```less
@color: "red";
.class {
  color: e(@color);
}
```

Built In Functions

lessphp has a collection of built in functions:

• e(str) -- returns a string without the surrounding quotes. See String Unquoting

• floor(number) -- returns the floor of a numerical input

• round(number) -- returns the rounded value of numerical input

• lighten(color, percent) -- lightens color by percent and returns it

• darken(color, percent) -- darkens color by percent and returns it

• saturate(color, percent) -- saturates color by percent and returns it

• desaturate(color, percent) -- desaturates color by percent and returns it

• fadein(color, percent) -- makes color less transparent by percent and returns it

• fadeout(color, percent) -- makes color more transparent by percent and returns it

• spin(color, amount) -- returns a color with amount degrees added to hue

• fade(color, amount) -- returns a color with the alpha set to amount

• hue(color) -- returns the hue of color

• saturation(color) -- returns the saturation of color

• lightness(color) -- returns the lightness of color

• alpha(color) -- returns the alpha value of color or 1.0 if it doesn't have an alpha

• percentage(number) -- converts a floating point number to a percentage, e.g. 0.65 -> 65%

• mix(color1, color1, percent) -- mixes two colors by percentage where 100% keeps all of color1, and 0% keeps all of color2. Will take into account the alpha of the colors if it exists. See http://sass-lang.com/docs/yardoc/Sass/Script/Functions.html#mix-instance_method.

• rgbahex(color) -- returns a string containing 4 part hex color.

This is used to convert a CSS color into the hex format that IE's filter method expects when working with an alpha component.

   ```less
   .class {
      @start: rgbahex(rgba(25, 34, 23, .5));
      @end: rgbahex(rgba(85, 74, 103, .6));
      // abridged example
      -ms-filter:
        e("gradient(start=@{start},end=@{end})");
   }
   ```

PHP Interface

When working with lessphp from PHP, the typical flow is to create a new instance of lessc, configure it how you like, then tell it to compile something using one built in compile methods.

Methods:

• compile($string) -- Compile a string

• compileFile($inFile, [$outFile]) -- Compile a file to another or return it

• checkedCompile($inFile, $outFile) -- Compile a file only if it's newer

• cachedCompile($cacheOrFile, [$force]) -- Conditionally compile while tracking imports

• setFormatter($formatterName) -- Change how CSS output looks

• setPreserveComments($keepComments) -- Change if comments are kept in output

• registerFunction($name, $callable) -- Add a custom function

• unregisterFunction($name) -- Remove a registered function

• setVariables($vars) -- Set a variable from PHP

• unsetVariable($name) -- Remove a PHP variable

• setImportDir($dirs) -- Set the search path for imports

• addImportDir($dir) -- Append directory to search path for imports

Compiling

The compile method compiles a string of LESS code to CSS.

```php
<?php
require "lessc.inc.php";

$less = new lessc;
echo $less->compile(".block { padding: 3 + 4px }");
```

The compileFile method reads and compiles a file. It will either return the result or write it to the path specified by an optional second argument.

```php
echo $less->compileFile("input.less");
```

The compileChecked method is like compileFile, but it only compiles if the output file doesn't exist or it's older than the input file:

```php
$less->checkedCompile("input.less", "output.css");
```

See Compiling Automatically for a description of the more advanced cachedCompile method.

Output Formatting

Output formatting controls the indentation of the output CSS. Besides the default formatter, two additional ones are included and it's also easy to make your own.

To use a formatter, the method setFormatter is used. Just pass the name of the formatter:

```php
$less = new lessc;

$less->setFormatter("compressed");
echo $less->compile("div { color: lighten(blue, 10%) }");
```

In this example, the compressed formatter is used. The formatters are:

• lessjs (default) -- Same style used in LESS for JavaScript

• compressed -- Compresses all the unrequired whitespace

• classic -- lessphp's original formatter

To revert to the default formatter, call setFormatter with a value of null.

Custom Formatter

The easiest way to customize the formatter is to create your own instance of an existing formatter and alter its public properties before passing it off to lessphp. The setFormatter method can also take an instance of a formatter.

Each of the formatter names corresponds to a class with lessc_formatter_ prepended in front of it. Here the classic formatter is customized to use tabs instead of spaces:

```php
$formatter = new lessc_formatter_classic;
$formatter->indentChar = "\t";

$less = new lessc;
$less->setFormatter($formatter);
echo $less->compileFile("myfile.less");
```

For more information about what can be configured with the formatter consult the source code.

Preserving Comments

By default, all comments in the source LESS file are stripped when compiling. You might want to keep the /* */ comments in the output though. For example, bundling a license in the file.

Enable or disable comment preservation by calling setPreserveComments:

```php
$less = new lessc;
$less->setPreserveComments(true);
echo $less->compile("/* hello! */");
```

Comments are disabled by default because there is additional overhead, and more often than not they aren't needed.

Compiling Automatically

Often, you want to only compile a LESS file only if it has been modified since last compile. This is very important because compiling is performance intensive and you should avoid a recompile if it possible.

The checkedCompile compile method will do just that. It will check if the input file is newer than the output file, or if the output file doesn't exist yet, and compile only then.

```php
$less->checkedCompile("input.less", "output.css");
```

There's a problem though. checkedCompile is very basic, it only checks the input file's modification time. It is unaware of any files from @import.

For this reason we also have cachedCompile. It's slightly more complex, but gives us the ability to check changes to all files including those imported. It takes one argument, either the name of the file we want to compile, or an existing cache object. Its return value is an updated cache object.

If we don't have a cache object, then we call the function with the name of the file to get the initial cache object. If we do have a cache object, then we call the function with it. In both cases, an updated cache object is returned.

The cache object keeps track of all the files that must be checked in order to determine if a rebuild is required.

The cache object is a plain PHP array. It stores the last time it compiled in $cache["updated"] and output of the compile in $cache["compiled"].

Here we demonstrate creating an new cache object, then using it to see if we have a recompiled version available to be written:

```php
$inputFile = "myfile.less";
$outputFile = "myfile.css";

$less = new lessc;

// create a new cache object, and compile
$cache = $less->cachedCompile($inputFile);

file_put_contents($outputFile, $cache["compiled"]);

// the next time we run, write only if it has updated
$last_updated = $cache["updated"];
$cache = $less->cachedCompile($cache);
if ($cache["updated"] > $last_updated) {
    file_put_contents($outputFile, $cache["compiled"]);
}

```

In order for the system to fully work, we must save cache object between requests. Because it's a plain PHP array, it's sufficient to serialize it and save it the string somewhere like a file or in persistent memory.

An example with saving cache object to a file:

```php
function autoCompileLess($inputFile, $outputFile) {
  // load the cache
  $cacheFile = $inputFile.".cache";

  if (file_exists($cacheFile)) {
    $cache = unserialize(file_get_contents($cacheFile));
  } else {
    $cache = $inputFile;
  }

  $less = new lessc;
  $newCache = $less->cachedCompile($cache);

  if (!is_array($cache) || $newCache["updated"] > $cache["updated"]) {
    file_put_contents($cacheFile, serialize($newCache));
    file_put_contents($outputFile, $newCache['compiled']);
  }
}

autoCompileLess('myfile.less', 'myfile.css');
```

cachedCompile method takes an optional second argument, $force. Passing in true will cause the input to always be recompiled.

Error Handling

All of the compile methods will throw an Exception if the parsing fails or there is a compile time error. Compile time errors include things like passing incorrectly typed values for functions that expect specific things, like the color manipulation functions.

```php
$less = new lessc;
try {
    $less->compile("} invalid LESS }}}");
} catch (Exception $ex) {
    echo "lessphp fatal error: ".$ex->getMessage();
}
```

Setting Variables From PHP

Before compiling any code you can set initial LESS variables from PHP. The setVariables method lets us do this. It takes an associative array of names to values. The values must be strings, and will be parsed into correct CSS values.

```php
$less = new lessc;

$less->setVariables(array(
  "color" => "red",
  "base" => "960px"
));

echo $less->compile(".magic { color: @color;  width: @base - 200; }");
```

If you need to unset a variable, the unsetVariable method is available. It takes the name of the variable to unset.

```php
$less->unsetVariable("color");
```

Be aware that the value of the variable is a string containing a CSS value. So if you want to pass a LESS string in, you're going to need two sets of quotes. One for PHP and one for LESS.

```php
$less->setVariables(array(
  "url" => "'http://example.com.com/'"
));

echo $less->compile("body { background: url("@{url}/bg.png"); }");
```

Import Directory

When running the @import directive, an array of directories called the import search path is searched through to find the file being asked for.

By default, when using compile, the import search path just contains "", which is equivalent to the current directory of the script. If compileFile is used, then the directory of the file being compiled is used as the starting import search path.

Two methods are available for configuring the search path.

setImportDir will overwrite the search path with its argument. If the value isn't an array it will be converted to one.

In this example, @import "colors"; will look for either assets/less/colors.less or assets/bootstrap/colors.less in that order:

```php
$less->setImportDir(array("assets/less/", "assets/bootstrap");

echo $less->compile('@import "colors";');
```

addImportDir will append a single path to the import search path instead of overwritting the whole thing.

```php
$less->addImportDir("public/stylesheets");
```

Custom Functions

lessphp has a simple extension interface where you can implement user functions that will be exposed in LESS code during the compile. They can be a little tricky though because you need to work with the lessphp type system.

The two methods we are interested in are registerFunction and unregisterFunction. registerFunction takes two arguments, a name and a callable value. unregisterFunction just takes the name of an existing function to remove.

Here's an example that adds a function called double that doubles any numeric argument:

```php
<?php
include "lessc.inc.php";

function lessphp_double($arg) {
    list($type, $value) = $arg;
    return array($type, $value*2);
}

$less = new lessc;
$less->registerFunction("double", "lessphp_double");

// gives us a width of 800px
echo $less->compile("div { width: double(400px); }");
```

The second argument to registerFunction is any callable value that is understood by call_user_func.

If we are using PHP 5.3 or above then we are free to pass a function literal like so:

```php
$less->registerFunction("double", function($arg) {
    list($type, $value) = $arg;
    return array($type, $value*2);
});
```

Now let's talk about the double function itself.

Although a little verbose, the implementation gives us some insight on the type system. All values in lessphp are stored in an array where the 0th element is a string representing the type, and the other elements make up the associated data for that value.

The best way to get an understanding of the system is to register is dummy function which does a var_dump on the argument. Try passing the function different values from LESS and see what the results are.

The return value of the registered function must also be a lessphp type, but if it is a string or numeric value, it will automatically be coerced into an appropriate typed value. In our example, we reconstruct the value with our modifications while making sure that we preserve the original type.

The instance of lessphp itself is sent to the registered function as the second argument in addition to the arguments array.

Command Line Interface

lessphp comes with a command line script written in PHP that can be used to invoke the compiler from the terminal. On Linux an OSX, all you need to do is place plessc and lessc.inc.php somewhere in your PATH (or you can run it in the current directory as well). On windows you'll need a copy of php.exe to run the file. To compile a file, input.less to CSS, run:

```bash
$ plessc input.less
```

To write to a file, redirect standard out:

```bash
$ plessc input.less > output.css
```

To compile code directly on the command line:

```bash
$ plessc -r "@color: red; body { color: @color; }"
```

To watch a file for changes, and compile it as needed, use the -w flag:

```bash
$ plessc -w input-file output-file
```

Errors from watch mode are written to standard out.

License

Copyright (c) 2012 Leaf Corcoran, http://leafo.net/lessphp

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Also under GPL3 if required, see LICENSE file