In the interpreter pattern you define a language, parse requests in that language, and assign the appropriate class(es), method(s), etc to handle each request.
In this example, the Interpreter class can handle strings in the following formats: "book author #", "book title #", or "book author title #". The # must be a numeric which must correlate to a book in the list of books we have.
. PHP Design Patterns . PHP Design Patterns Interpreter
PHP Design Patterns Interpreter
About the Intrepreter
Interpreter.php
//copyright Lawrence Truett and FluffyCat.com 2005, all rights reserved
include_once('BookList.php');
class Interpreter {
private $bookList;
public function __construct($bookListIn) {
$this->bookList = $bookListIn;
}
public function interpret($stringIn) {
$arrayIn = explode(" ",$stringIn);
$returnString = NULL;
//go through the array validating
// and if possible calling a book method
//could use refactoring, some duplicate logic
if ('book' == $arrayIn[0]) {
if ('author' == $arrayIn[1]) {
if (is_numeric($arrayIn[2])) {
$book = $this->bookList->getBook($arrayIn[2]);
if (NULL == $book) {
$returnString = 'Can not process, there is no book # '.
$arrayIn[2];
} else {
$returnString = $book->getAuthor();
}
} elseif ('title' == $arrayIn[2]) {
if (is_numeric($arrayIn[3])) {
$book = $this->bookList->getBook($arrayIn[3]);
if (NULL == $book) {
$returnString = 'Can not process, there is no book # '.
$arrayIn[3];
} else {
$returnString = $book->getAuthorAndTitle();
}
} else {
$returnString =
'Can not process, book # must be numeric.';
}
} else {
$returnString = 'Can not process, book # must be numeric.';
}
}
if ('title' == $arrayIn[1]) {
if (is_numeric($arrayIn[2])) {
$book = $this->bookList->getBook($arrayIn[2]);
if (NULL == $book) {
$returnString = 'Can not process, there is no book # '.
$arrayIn[2];
} else {
$returnString = $book->getTitle();
}
} else {
$returnString = 'Can not process, book # must be numeric.';
}
}
} else {
$returnString = 'Can not process, '.
'can only process book author #, book title #, or book author title #';
}
return $returnString;
}
}
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BookList.php
//copyright Lawrence Truett and FluffyCat.com 2005, all rights reserved
include_once('Book.php');
class BookList {
private $books = array();
private $bookCount = 0;
public function __construct() {
}
public function getBookCount() {
return $this->bookCount;
}
private function setBookCount($newCount) {
$this->bookCount = $newCount;
}
public function getBook($bookNumberToGet) {
if ( (is_numeric($bookNumberToGet)) &&
($bookNumberToGet <= $this->getBookCount())) {
return $this->books[$bookNumberToGet];
} else {
return NULL;
}
}
public function addBook(Book $book_in) {
$this->setBookCount($this->getBookCount() + 1);
$this->books[$this->getBookCount()] = $book_in;
return $this->getBookCount();
}
public function removeBook(Book $book_in) {
$counter = 0;
while (++$counter <= $this->getBookCount()) {
if ($book_in->getAuthorAndTitle() ==
$this->books[$counter]->getAuthorAndTitle())
{
for ($x = $counter; $x < $this->getBookCount(); $x++) {
$this->books[$x] = $this->books[$x + 1];
}
$this->setBookCount($this->getBookCount() - 1);
}
}
return $this->getBookCount();
}
}
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Book.php
//copyright Lawrence Truett and FluffyCat.com 2005, all rights reserved
class Book {
private $author;
private $title;
function __construct($title_in, $author_in) {
$this->author = $author_in;
$this->title = $title_in;
}
function getAuthor() {return $this->author;}
function getTitle() {return $this->title;}
function getAuthorAndTitle() {
return $this->getTitle() . ' by ' . $this->getAuthor();
}
}
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testInterpreter.php
//copyright Lawrence Truett and FluffyCat.com 2006, all rights reserved
include_once('Interpreter.php');
include_once('BookList.php');
include_once('Book.php');
define('BR', '<'.'BR'.'>');
echo 'BEGIN TESTING INTERPRETER PATTERN'.BR;
echo BR;
//load BookList for test data
$bookList = new BookList();
$inBook1 = new Book('PHP for Cats','Larry Truett');
$inBook2 = new Book('MySQL for Cats','Larry Truett');
$bookList->addBook($inBook1);
$bookList->addBook($inBook2);
$interpreter = new Interpreter($bookList);
echo 'test 1 - invalid request missing "book"'.BR;
echo $interpreter->interpret('author 1');
echo BR.BR;
echo 'test 2 - valid book author request'.BR;
echo $interpreter->interpret('book author 1');
echo BR.BR;
echo 'test 3 - valid book title request'.BR;
echo $interpreter->interpret('book title 2');
echo BR.BR;
echo 'test 4 - valid book author title request'.BR;
echo $interpreter->interpret('book author title 1');
echo BR.BR;
echo 'test 5 - invalid request with invalid book number'.BR;
echo $interpreter->interpret('book title 3');
echo BR.BR;
echo 'test 6 - invalid request with nuo numeric book number'.BR;
echo $interpreter->interpret('book title one');
echo BR.BR;
echo 'END TESTING INTERPRETER PATTERN'.BR;
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output of testInterpreter.php
BEGIN TESTING INTERPRETER PATTERN
test 1 - invalid request missing "book" Can not process, can only process book author #, book title #, or book author title #
test 2 - valid book author request Larry Truett
test 3 - valid book title request MySQL for Cats
test 4 - valid book author title request PHP for Cats by Larry Truett
test 5 - invalid request with invalid book number Can not process, there is no book # 3
test 6 - invalid request with nuo numeric book number Can not process, book # must be numeric.
END TESTING INTERPRETER PATTERN
References
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