Formal Languages Block
Authors
- Idea, string analysis method, general architecture and architecture implementation - Oleg Sychev
- Implementation of built-in language - Dmitry Mamontov
Description
The goal of formal languages block is to provide an API for managing formal languages - a well-known mathematical formalism, that defines a set of strings, constrained by rules.
Сurrent status
| Feature | Description | Status |
|---|---|---|
| Scanning | Breaks string into tokens, that can be useful in further analysis | Implemented |
| Parsing | Constructs abstract syntax tree from a string, allowing deep analysis of string or even performing evaluation | Not implemented |
| Managing formal languages | Currently C, C++, printf format string scanners are implemented. Also implemented simple lexer for english language. User-defined lexers and parser are going to be implemented in next releases. | Implemented partially |
Current language implementation status
| Language | Scanning | Parsing |
|---|---|---|
| Simple english | Implemented | Not implemented |
| C | Implemented | Not implemented |
| C++ | Implemented | Implemented partially |
| printf formatting string | Implemented | Not implemented |
Installation
To work CorrectWriting question type needs some additional components. They all need to be installed in order for question to work. You could download all them in one archive (from GoogleCode) or separately.
If you downloaded one archive, unpacking it you should found "question" and "blocks" folders. Copy them in the main directory of Moodle installation (the one containing config.php) - it will install everything in the correct places.
If you downloaded all parts separately (for example because Moodle plugins Directory don't allow them to be downloaded together), you should get 3 archives. Place "correctwriting" and "poasquestion" folders in the question/type folder of Moodle installation. "formal_langs" should be placed in the blocks folder.
After having files in place login as administrator and go to the notifications page.
User interface
After adding formal languages block to course, a teacher could manage language visibilty by clicking on eye icons. The dimmed languages with disabled visibility will not be shown in CorrectWriting or other plugins, that use API of formal language block.
Note, that language visibility can be inherited from site settings. So, when site setting is applied to current course, user will see label "(Site)" before name of language, and "(Course)" if setting is applied to course. Note, that block tries to keep settings in database as short as possible, so if current course setting for language matches site setting for langugage, it will be removed and visibility will be taken from site visibility setting. If it does not match, setting will be applied on course level.
Administrator also, can edit global visibility of formal languages, using global settings, located in administrator menu (see pictures for details).
A central part of admin page will look just like below.
API for developers
A main block class - block_formal_langs provides a two simple functions, that might be useful for someone, that want to use our API to perform string scanning (see CorrectWriting question type examples to see how it works).
- block_formal_langs::available_langs - returns array of languages, that could be used in current context. Receives current context ID.
- block_formal_langs::lang_object - returns language object by language ID.
After getting language object, you can use create_from_string or create_from_db to scan string without referring to descriptions in database or refer to them. This will return a special object, that can be used for working with lexemes.
If $a is object, returned by create_from_string or create_from_db, you can use $a->string to get scanned string, $a->stream->tokens to return array of scanned lexemes, $a->stream->errors to get array of errors.
Using scanned lexemes, you could use type() method to obtain special type of lexeme, or value() to obtain a semantic value for lexeme.
Example:
1. You can use following code to print names and ids of all available languages in system context.
$langs = block_formal_langs::available_langs( context_system::instance()->id );
foreach($langs as $id => $name)
{
echo 'id :' . $id . ' name: ' . $name . PHP_EOL;
}
2. You can use following code to print all tokens' text, scanned a string with C language lexer.
$lang = block_formal_langs::lang_object(2); // Id for C programming language in most databases will be 2
$string = $lang->create_from_string('int a;');
$tokens = $string->stream->tokens;
foreach($tokens as $token)
{
echo $token->value() . PHP_EOL;
}
