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Lisphp is a Lisp dialect written in PHP.

branch: master
README.markdown

Lisphp

Lisphp is a Lisp dialect written in PHP. It was created to be embedded in web services or to be distributed within web applications. For that reason, it implements sandbox environment for security issues and multiple environment instances.

Requirements

It requires PHP 5.2.5 or higher version. When it works on PHP 5.3 or higher, it is integrated with lambda functions well. It also requires SPL which is available and compiled by default in PHP 5.

Standalone command line interface

There is lis.php, a standalone command line interface. It can take one parameter, the filename of the Lisphp program to be executed.

$ php lis.php program.lisphp

You can run the program in sandbox with the option -s.

$ php lis.php -s program.lisphp

REPL

If there is no filename in arguments to lis.php, it enters REPL mode.

$ php lis.php
>>> (form to evaulate)

Similarly you can specify -s to enter REPL mode in sandbox.

$ php lis.php -s
  • >>> is a prompt.
  • ==> is a returned value of evaluation.
  • !!! is a thrown exception.

Simple tutorial

>>> (+ 12 34)
==> 46
>>> (- 1 2)
==> -1
>>> (* 5 6)
==> 30
>>> (/ 30 5)
==> 6
>>> (/ 30 4)
==> 7.5
>>> (% 30 4)
==> 2
>>> (. "hello" "world")
==> 'helloworld' 
>>> (define pi 3.14)
==> 3.14
>>> pi
==> 3.14
>>> (float? pi)
==> true
>>> (string? "abc")
==> true
>>> (* pi 10 10)
==> 314

Embed in your app

In order to execute a Lisphp program, an environment instance is required. Environment represents a global state for the program. It includes global symbols, built-in functions and macros. A program to be executed starts from the initialized environment. You can initialize the environment with Lisphp_Environment class.

require_once 'Lisphp.php';
$env = Lisphp_Environment::sandbox();
$program = new Lisphp_Program($lisphpCode);
$program->execute($env);

There are two given environment sets in Lisphp_Environment. One is the sandbox, which is created with the method Lisphp_Environment::sandbox(). In the sandbox mode, programs cannot access the file system, IO, etc. The other set is the full environment of Lisphp, which is initialized with Lisphp_Environment::full(). This environment provides use macro for importing native PHP functions and classes. File system, IO, socket, etc. can be accessed in this full environment. Following code touches file a.txt and writes some text.

(use fopen fwrite fclose)

{let [fp (fopen "a.txt" "w")]
     (fwrite fp "some text")
     (fclose fp)}

Macro use and from

The full environment of Lisphp provides use macro. It can import native PHP functions and classes.

(use strrev array_sum array-product [substr substring])

It imports by taking function identifiers. Hyphens in identifiers are replaced by underscores. If you supply a list as an argument to use macro, the second symbol becomes the alias of the first function identifier.

(strrev "hello")                #=> "olleh"
(array_sum [array 1 2 3])       #=> 6
(array-product [array 4 5 6])   #=> 120
(substring "world" 2)           #=> "rld"

Wrap identifiers with angle brackets in order to import class. According to the PEAR naming convention for classes, slashes are treated as hierarchical separators, so it gets replaced by underscores.

(use <PDO> Lisphp/<Program>)

Imported classes are applicable and act as instantiating functions. Static methods in imported classes are also imported as well.

(<PDO> "mysql:dbname=testdb;host=127.0.0.1" "dbuser" "dbpass")
(Lisphp/<Program>/load "program.lisphp")

There's also a macro called from. It simplifies the step of importing objects and resolving their names.

(from Lisphp [<Program> <Scope>])

It has the same behavior as the following code which utilizes use.

(use Lisphp/<Program> Lisphp/<Scope>)
(define <Program> Lisphp/<Program>)
(define <Scope> Lisphp/<Scope>)
(define Lisphp/<Program> nil)
(define Lisphp/<Scope> nil)

Define custom functions

There is a macro lambda that creates a new function. It takes parameter list as its first argument, and then a trailing function body.

(lambda (a b) (+ a b))

Functions are also values, so in order to name the function, use define.

(define fibonacci
        {lambda [n]
                (if (= n 0) 0
                    {if (/= n 1)
                        (+ (fibonacci (- n 1))
                           (fibonacci (- n 2)))
                        1})})

Following code defines the same function.

(define (fibonacci n)
        (if (= n 0) 0
            {if (/= n 1)
                (+ (fibonacci (- n 1))
                   (fibonacci (- n 2)))
                1}))

Function body can contain one or more forms. All forms are evaluated sequentially then the evaluated value of the last form is returned.

Plus, of course, it implements lexical scope (that is also known as closure) also.

(define (adder n)
        {lambda [x]
                (setf! n (+ n x))
                n})

Special form define defines global variables (and functions), but setf! modifies local variables. See also let form.

Define custom macros

The built-in macros in Lisphp such as eval, define, lambda, let, if, and, or do not evaluate the form of their arguments'. For example, define takes the name to define as its first argument, but it does not evaluate the name. In the same way, if takes three forms as arguments, but always evaluates only two of those arguments and ignores the other. It is impossible to implement if as a function, because then every argument would have to be evaluated. If you have a case like this, you can try defining a macro.

(define if*
        {macro [let {(cond (eval (car #arguments)
                                 #scope))}
                    (eval (at #arguments (or (and cond 1) 2))
                          #scope)]})

(define quote*
        [macro (car #arguments)])

Quote

There are two ways to quote a form in Lisphp. First is the macro quote, and the other is quote syntax :. (You cannot use the traditional single quotation because it is already being used as a string literal.)

(quote abc)
:abc
(quote (+ a b))
:(+ a b)

Playing with objects

In order to get an attribute of an object, use -> macro. It takes an object as its first argument, and the name of the attribute follows.

(use [dir <dir>])
(define directory (<dir> "/tmp"))
(define handle (-> directory handle))

There is also a syntactic sugar for object attribute chaining.

(-> object attribute names go here)

This form is equivalent to the following PHP expression.

$object->attribute->names->go->here

Instance methods can also be invoked by ->.

((-> object method) method arguments)

This form is equivalent to the following PHP expression.

$object->method($method, $arguments)

Because -> does not call but gets method as a function object, the expression above is equivalent to the following code.

call_user_func(array($object, 'method'), $method, $arguments)

About lists and nil

Lisphp implements lists in primitive, but it has some differences between original Lisp. In original Lisp, lists are made from cons pairs. But lists in Lisphp is just an instance of Lisphp_List class, a subclass of ArrayObject. So it is not exactly a linked list but is similar to an array. In the same manner, nilis also not an empty list in Lisphp unlike in the original Lisp. It is a just synonym for PHP null value.

About value types and reference types

In PHP, primitive types such as boolean, integer, float, string, and array behave as value types. They are always copied when they are passed as arguments or returned from a called function. For example, arr is empty from the beginning to the end in the following code.

(define arr (array))
(set-at! arr "element")

Such behavior is not a problem for scalar types like boolean, integer, float, and string because they are immutable. Yet this can be problematic for native arrays.

In PHP, objects behave as reference types, and there exists class ArrayObject which has the same interface as PHP's native array. Lisphp_List is a subclass of ArrayObject and you can use these classes instead of arrays.

(use <ArrayObject>)
(define arr (<ArrayObject>))
(set-at! arr "element")
(define lis (list))
(set-at! arr "element")

Mailing list

There is the mailing list to discuss about Lisphp: lisphp@googlegroups.com.

The web archive for this mailing list: http://groups.google.com/group/lisphp.

Author and license

Lisphp was written by Hong Minhee http://dahlia.kr/.

Lisphp is distributed under the MIT license.

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