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The Hoa\Compiler library. 2017-08-08 07:44 UTC



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Hoa is a modular, extensible and structured set of PHP libraries.
Moreover, Hoa aims at being a bridge between industrial and research worlds.


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This library allows to manipulate LL(1) and LL(k) compiler compilers. A dedicated grammar description language is provided for the last one: the PP language.

Learn more.


With Composer, to include this library into your dependencies, you need to require hoa/compiler:

$ composer require hoa/compiler '~3.0'

For more installation procedures, please read the Source page.


Before running the test suites, the development dependencies must be installed:

$ composer install

Then, to run all the test suites:

$ vendor/bin/hoa test:run

For more information, please read the contributor guide.

Quick usage

As a quick overview, we will look at the PP language and the LL(k) compiler compiler.

The PP language

A grammar is constituted by tokens (the units of a word) and rules (please, see the documentation for an introduction to the language theory). The PP language declares tokens with the following construction:

%token [source_namespace:]name value [-> destination_namespace]

The default namespace is default. The value of a token is represented by a PCRE. We can skip tokens with the %skip construction.

As an example, we will take the simplified grammar of the JSON language. The complete grammar is in the hoa://Library/Json/Grammar.pp file. Thus:

%skip   space          \s
// Scalars.
%token  true           true
%token  false          false
%token  null           null
// Strings.
%token  quote_         "        -> string
%token  string:string  [^"]+
%token  string:_quote  "        -> default
// Objects.
%token  brace_         {
%token _brace          }
// Arrays.
%token  bracket_       \[
%token _bracket        \]
// Rest.
%token  colon          :
%token  comma          ,
%token  number         \d+

    <true> | <false> | <null> | string() | object() | array() | number()

    ::quote_:: <string> ::_quote::


    ::brace_:: pair() ( ::comma:: pair() )* ::_brace::

    string() ::colon:: value()

    ::bracket_:: value() ( ::comma:: value() )* ::_bracket::

We can see the PP constructions:

  • rule() to call a rule;
  • <token> and ::token:: to declare a token;
  • | for a disjunction;
  • (…) to group multiple declarations;
  • e? to say that e is optional;
  • e+ to say that e can appear at least 1 time;
  • e* to say that e can appear 0 or many times;
  • e{x,y} to say that e can appear between x and y times;
  • #node to create a node the AST (resulting tree);
  • token[i] to unify tokens value between them.

Unification is very useful. For example, if we have a token that expresses a quote (simple or double), we could have:

%token  quote   "|'
%token  handle  \w+

    ::quote:: <handle> ::quote::

So, the data "foo" and 'foo' will be valid, but also "foo' and 'foo"! To avoid this, we can add a new constraint on token value by unifying them, thus:

    ::quote[0]:: <handle> ::quote[0]::

All quote[0] for the rule instance must have the same value. Another example is the unification of XML tags name.

LL(k) compiler compiler

The Hoa\Compiler\Llk\Llk class provide helpers to manipulate (load or save) a compiler. The following code will use the previous grammar to create a compiler, and we will parse a JSON string. If the parsing succeed, it will produce an AST (stands for Abstract Syntax Tree) we can visit, for example to dump the AST:

// 1. Load grammar.
$compiler = Hoa\Compiler\Llk\Llk::load(new Hoa\File\Read('Json.pp'));

// 2. Parse a data.
$ast = $compiler->parse('{"foo": true, "bar": [null, 42]}');

// 3. Dump the AST.
$dump = new Hoa\Compiler\Visitor\Dump();
echo $dump->visit($ast);

 * Will output:
 *     >  #object
 *     >  >  #pair
 *     >  >  >  token(string, foo)
 *     >  >  >  token(true, true)
 *     >  >  #pair
 *     >  >  >  token(string, bar)
 *     >  >  >  #array
 *     >  >  >  >  token(null, null)
 *     >  >  >  >  token(number, 42)

Pretty simple.

Compiler in CLI

This library proposes a script to parse and apply a visitor on a data with a specific grammar. Very useful. Moreover, we can use pipe (because Hoa\File\Read —please, see the Hoa\File library— supports 0 as stdin), thus:

$ echo '[1, [1, [2, 3], 5], 8]' | hoa compiler:pp Json.pp 0 --visitor dump
>  #array
>  >  token(number, 1)
>  >  #array
>  >  >  token(number, 1)
>  >  >  #array
>  >  >  >  token(number, 2)
>  >  >  >  token(number, 3)
>  >  >  token(number, 5)
>  >  token(number, 8)

You can apply any visitor classes.


Errors are well-presented:

$ echo '{"foo" true}' | hoa compiler:pp Json.pp 0 --visitor dump
Uncaught exception (Hoa\Compiler\Exception\UnexpectedToken):
Hoa\Compiler\Llk\Parser::parse(): (0) Unexpected token "true" (true) at line 1
and column 8:
{"foo" true}
in hoa://Library/Compiler/Llk/Parser.php at line 1


Some algorithms are available to generate data based on a grammar. We will give only one example with the coverage-based generation algorithm that will activate all branches and tokens in the grammar:

$sampler = new Hoa\Compiler\Llk\Sampler\Coverage(
    // Grammar.
    Hoa\Compiler\Llk\Llk::load(new Hoa\File\Read('Json.pp')),
    // Token sampler.
    new Hoa\Regex\Visitor\Isotropic(new Hoa\Math\Sampler\Random())

foreach ($sampler as $i => $data) {
    echo $i, ' => ', $data, "\n";

 * Will output:
 *     0 => true
 *     1 => {" )o?bz " : null , " %3W) " : [false, 130    , " 6"   ]  }
 *     2 => [{" ny  " : true } ]
 *     3 => {" Ne;[3 " :[ true , true ] , " th: " : true," C[8} " :   true }

Research papers


The hack book of Hoa\Compiler contains detailed information about how to use this library and how it works.

To generate the documentation locally, execute the following commands:

$ composer require --dev hoa/devtools
$ vendor/bin/hoa devtools:documentation --open

More documentation can be found on the project's website: hoa-project.net.

Getting help

There are mainly two ways to get help:


Do you want to contribute? Thanks! A detailed contributor guide explains everything you need to know.


Hoa is under the New BSD License (BSD-3-Clause). Please, see LICENSE for details.