CL O X : Common Lisp Objects for XEmacs Motivation Alternatives - PowerPoint PPT Presentation

CL O X Didier Verna Introduction Context CL O X : Common Lisp Objects for XEmacs Motivation Alternatives Closette ELisp vs. Lisp The CL package Didier Verna Scoping λ -lists Type/Class didier@xemacs.org Types http://www.xemacs.org Generic Functions http://www.lrde.epita.fr/˜didier Project status Available Features Testing Performance ELS 2010 – Friday, May 7th Conclusion Thanks ! 1/33

Overview CL O X What is it ? Didier Verna ◮ An implementation of C LOS for XEmacs ◮ Including the Meta-Object Protocol (M OP ) Introduction Context What’s in it ? Motivation Alternatives ◮ A port of Closette to Emacs Lisp Closette ◮ Deeper type/class integration ELisp vs. Lisp The CL package ◮ A comprehensive test suite Scoping λ -lists Type/Class Types Generic Functions Project status Available Features Testing Performance Conclusion Thanks ! 2/33

Table of contents CL O X Didier Verna Introduction 1 Introduction Context Closette in Emacs Lisp Motivation 2 Alternatives Closette ELisp vs. Lisp Type/class integration 3 The CL package Scoping λ -lists Type/Class Project status 4 Types Generic Functions Project status Conclusion 5 Available Features Testing Performance Conclusion Thanks ! 4/33

Context The state of XEmacs CL O X About XEmacs Didier Verna ◮ Initially a fork of GNU Emacs v.19-to-be (1991) ◮ Greatly diverged since then Introduction Context ◮ User-level Emacs Lisp compatibility Motivation ◮ Internals compatibility Alternatives Closette About the internals ELisp vs. Lisp The CL package ◮ Very high level of abstraction Scoping ◮ 111 opaque Lisp types, 35 user-level λ -lists Type/Class ◮ Core in “C+”: data-abstraction and OO infrastructure Types Generic Functions Project status Available Features Testing Performance Conclusion Thanks ! 6/33

A couple of “C+” examples So why not use C++ directly ? *plonk* CL O X Polymorphism / Class-like abstraction Didier Verna Introduction struct console Context { Motivation Alternatives enum console_variant contype; void *console_data; Closette struct console_methods *conmeths; ELisp vs. Lisp The CL package / ∗ . . . ∗ / Scoping } λ -lists Type/Class Types Generic Functions Project status Dynamic method lookup Available Features Testing Performance MAYBE_CONMETH (console, mark_console, ...); Conclusion Thanks ! 7/33

Motivation Bring the same level of abstraction to the Lisp layer CL O X Why isn’t it the case already ? Didier Verna ◮ GNU Emacs compatibility ◮ Emacs Lisp backward compatibility Introduction ◮ Less “OO pressure” at the Lisp level Context Motivation • Glue to the C level Alternatives • Not the job of package authors Closette ELisp vs. Lisp • Requires more than the average coding skill The CL package • Ad-hoc abstraction easier to achieve in Lisp Scoping λ -lists What would be the benefits ? Type/Class Types ◮ C-based features: abstract away the Lisp glue Generic Functions ◮ Lisp features: improve maintainability / extensibility Project status ◮ Also for third-party packages ( e.g. Gnus) Available Features Testing Performance Conclusion Thanks ! 8/33

Why C LOS ? Arguments in favor of it CL O X 1 Emacs Lisp Didier Verna ◮ Close to MacLisp and Common Lisp ◮ Many developers familiar with Common Lisp Introduction Context ◮ CL package dependency: 16% files, 27% LoC Motivation Alternatives 2 C LOS Closette ◮ One of the most powerful object system around ELisp vs. Lisp The CL package ◮ Well documented Scoping ◮ No need to start from scratch λ -lists Type/Class 3 Porting Common Lisp libraries to Emacs Lisp Types Generic Functions 4 Attract more Common Lisp developers Project status Available Features 5 Gain expertise in C LOS and its M OP ;-) Testing Performance Conclusion Thanks ! 9/33

Alternatives Other available object systems CL O X 1 E OOPS (Emacs Lisp Object Oriented Programming System) Didier Verna ◮ Message passing (Smalltalk style) ◮ No activity since 1992 Introduction Context ◮ No known Emacs Lisp package using it Motivation Alternatives 2 E IEIO (Enhanced Implementation of Emacs Interpreted Objects) Closette ◮ Active ELisp vs. Lisp The CL package ◮ Part of the C EDET package (70,000 LoC) Scoping ◮ C LOS -like λ -lists Type/Class ◮ Additional features ( e.g. debugging support) Types ◮ Doesn’t aim at being fully compliant Generic Functions Project status Available Features Testing Performance Conclusion Thanks ! 10/33

Emacs Lisp vs. Common Lisp All them dialects, they make my head swim CL O X Fundamental differences Didier Verna ◮ Dynamic vs. lexical scope ◮ No package system, Limited λ -list syntax Introduction Context ◮ Different types, condition system, printing facilities etc. Motivation Alternatives Less obvious ones Closette ◮ Different function names ELisp vs. Lisp The CL package ◮ Similar functions with different semantics Scoping λ -lists ◮ function is different Type/Class (X)Emacs Lisp evolution Types Generic Functions ◮ Self-evaluating keywords since 1996 Project status ◮ #’ syntax since XEmacs 19.8 Available Features Testing ◮ Primitive character type since XEmacs 19.20 Performance ◮ Built-in multiple values since a couple of months Conclusion Thanks ! ◮ XEmacs no later than 21.5 beta 29 \ today is required 12/33

The CL package Common Lisp emulation layer CL O X Provide missing standard utility functions or macros Didier Verna ( e.g. loop ) Introduction Extend existing but limited ones Context Motivation ( e.g. mapcar* ) Alternatives Closette Support full λ -list syntax ELisp vs. Lisp ( defun* , defmacro* etc. ) The CL package Scoping λ -lists typep Type/Class setf / defsetf (no setf functions) Types Generic Functions Project status Available Features Testing Performance Conclusion Thanks ! 13/33

Dynamic vs. lexical scope A CL O X work Orange CL O X CL ’s lexical-let to the rescue Didier Verna Not necessary in most cases Introduction ◮ Local use of let bindings or function parameters Context ◮ “Downward funargs” situations Motivation Alternatives ◮ “Upward funargs” situations in some cases Closette ELisp vs. Lisp ◮ Only 6 actual uses of lexical-let The CL package Scoping λ -lists Type/Class Types Generic Functions Project status Available Features Testing Performance Conclusion Thanks ! 14/33

Downward funargs: example Look at the required-classes argument CL O X Didier Verna (defun compute-applicable-methods-using-classes (gf required-classes) Introduction #| . . . |# Context Motivation (remove-if-not #’(lambda (method) Alternatives (every #’subclassp Closette required-classes ELisp vs. Lisp (method-specializers method))) The CL package Scoping (generic-function-methods gf)) λ -lists #| . . . |# ) Type/Class Types Generic Functions Project status Available Features Testing Performance Conclusion Thanks ! 15/33

Upward funargs: example Look at the next-emfun argument CL O X Didier Verna (defun compute-primary-emfun (methods) (if (null methods) Introduction nil Context Motivation Alternatives ; ; Common Lisp version : Closette (let ((next-emfun (compute-primary-emfun (cdr methods)))) ELisp vs. Lisp #’(lambda (args) The CL package Scoping (funcall (method-function (car methods)) λ -lists args next-emfun))) Type/Class Types ; ; P a r t i a l l y evaluated Emacs Lisp version : Generic Functions (let ((next-emfun (compute-primary-emfun (cdr methods)))) Project status ‘(lambda (args) Available Features (funcall (method-function ’,(car methods)) Testing Performance args ’,next-emfun))) Conclusion Thanks ! 17/33

Upward funargs: explanation Look at the next-emfun argument CL O X Didier Verna ; ; P a r t i a l l y evaluated Emacs Lisp version : (let ((next-emfun (compute-primary-emfun (cdr methods)))) Introduction ‘(lambda (args) Context Motivation (funcall (method-function ’,(car methods)) Alternatives args ’,next-emfun))) Closette ELisp vs. Lisp The CL package Scoping lambda is self-quoting λ -lists Type/Class (lambda ...) is a function designator Types Generic Functions e.g. (funcall ’(lambda (x) x) 1) Project status function ⇐ ⇒ quote + byte-compiler hint Available Features Testing Performance Note: use byte-compile on the resulting form Conclusion Thanks ! 18/33