[parenscript-devel] Proposal: Package System

[Vladimir Sedach]

This sounds like the right way to go. I am also in agreement with
Henrik that providing a protocol into the relevant parts of the
package system would be a very valuable addition. The one thing I
think is critical is that ParenScript's current semantics with respect
to naming be preserved if you choose not to use the package system.

Vladimir

On 6/26/07, Red Daly <reddaly at gmail.com> wrote:
> Dear Fellow Parenscripters,
>
> Here I detail a proposed package system for Parenscript to ease modular
> development.  This is a feature intended to make up for the many hacks
> Javascript programmers use to write libraries.  The proposed system takes
> after and integrates with the Lisp package system.  Its implementation will
> constitute a hearty advancement of the current Parenscript compiler.
>
> The proposed system should introduce new concepts and should be robust
> enough to lay the foundation for a lot of future work in a coherent way.
> Different packages can introduce new special forms--that is, modify the
> language at the lowest level.  With this, a "javascript2" package can
> introduce Parenscript forms that compile to the latest version of ECMAScript
> without implicating the rest of the project.  The additional semantic
> analysis of Parenscript programs will pave the way for cropped, minified, or
> obfuscated scripts.  In addition, a formal package specification will lead
> to asdf-installable script libraries with better deployment characteristics
> than current package systems for web development in other languages.
>
> A Parenscript package (or "script package" or simply "package," as opposed
> to a "Lisp package") has a few main properties: a name and list of
> nicknames, an primary associated Lisp package, a list of exported
> identifiers, and a collection of macros defined in the associated Lisp
> package.  We must also introduce and formalize a two other concepts:
> Parenscript identifiers (analog of Lisp symbols), and a compilation
> environment.
>
> A Parenscript package is defined and exists in the context of a compilation
> environment.  A compilation environment simply keeps track of compiler
> state; when any Parenscript code is compiled, a new compilation environment
> is created or an existing one is passed to the compiler.  The environment is
> modified to reflect the lexical scope as forms are processed.  Specifically,
> the compilation environment will consist of a stack of Parenscript
> identifiers (introduced by defun and defvar forms); a stack of macros and
> symbol macros; a list of defined script packages; and the current script
> package.
>
> An identifier in Parenscript is analogous to a Lisp symbol, but it only
> exists during compile time.   An identifier has a string value and
> associated Parenscript package.
>
> Now I will run through a simple example to demonstrate these new
> developments:
>
> Script packages are primarily defined using a Parenscript form analogous to
> the Lisp defpackage:
>
> (defpackage friendly-script
>    (:use parenscript psos)
>    (:export hello-world)
>    (:lisp-package friendly)
>    (:documentation "Scripts for issuing greetings."))
>
> This introduces a new package into the compilation environment.  We enter
> the package system after it is defined as in Lisp:
>
> ;; enter the friendly-script package
> ; changes the current package in the compilation environment to
> :friendly-script
> (in-package :friendly-script)
>
> ;; define the hello-world function, which we export
> ; adds friendly-script::hello-world to the identifier stack in the
> compilation env.
> (defun hello-world ()
>    (alert "hello world."))
>
> ;; enter the user package
> ; changes current package in compilation environment
> (in-package :parenscript-user)
>
> ;; call the friendly-script's hello-world function
> ; the compiler recognizes that friendly-script::hello-world is an e
> (friendly-script:hello-world)
>
>
> To give you an idea, this will all compile to something like the following
> Javascript:
>
>
> function friendlyScript_helloWorld() { alert("hello world."); }
>
> friendlyScript_helloWorld();
>
>
> In terms of implementation, the package system will introduce a few new
> classes (script-package, identifier, and compilation-environment); uproot
> existing parsing procedures and replant them around the package system; and
> add a semantic analysis phase into the compilation pipeline.  I will fill in
> details and announce problems with the implementation as it moves forward.
>
> Hopefully this is an exciting prospect for the community.  The package
> system should empower those who want to build large programs or share
> Parenscript extensions/libraries.  It should also preserve the
> javascript-in-sexps Parenscript we know and love.
>
> Anyhow, I look forward to comments on this proposal.  Happy hacking!
>
> Red
>
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