Библиотека сайта или "Мой Linux Documentation Project"
Mixing languages is a knowledge-intensive (rather than coding-intensive) style of programming. To make it work, you have to have both working knowledge of a suitable variety of languages and expertise about what they're best at and how to fit them together. In this section, we will try to point you at references to help you with the first and an overview to convey the second. For each language surveyed we will include case studies of successful programs that exemplify its strengths.
Programs that must be portable across multiple operating systems may also be good candidates for C. Some of the alternatives to C that we shall discuss below are, however, increasingly penetrating major non-Unix operating systems; in the near future, portability may be less a distinguishing advantage of C.
Sometimes the leverage to be gained from existing programs like parser generators or GUI builders that generate C code is so great that it justifies C coding of the rest of a small application.
And, of course, C proved indispensable to the developers of all its alternatives. Dig down through enough implementation layers under any of the other languages surveyed here and you will find a core implemented in pure, portable C. These languages inherit many of the advantages of C.
One good reason to learn C, even if your programming needs are satisfied by a higher-level language, is that it can help you learn to think at hardware-architecture level. The best reference and tutorial on C for people who are already programmers is still The C Programming Language [Kernighan-Ritchie].
Porting C code between Unix variants is almost always possible and usually easy, but specific areas of variation (like signals and process control) can be tricky to get right. We highlight some of these issues in Chapter═17. Differing C bindings on other operating systems can of course cause C portability problems, although Windows NT at least theoretically supports an ANSI/POSIX-compliant C API.
High-quality C compilers are available as open-source software over the Internet; the best-known and most widely used is the Free Software Foundation's GNU C compiler (part of GCC, the GNU Compiler Collection), which has become the native C of all open-source Unix systems and many even in the closed-source world. GCC ports are even available for Microsoft's family of operating systems. GCC sources are available at the FSF's FTP site.
Summing up: C's best side is resource efficiency and closeness to the machine. Its worst side is that programming in it is a resource-management hell.
C Case Study: fetchmail
The best case study for C is the Unix kernel itself, for which a language that naturally supports hardware-level operations is actually a strong advantage. But fetchmail is a good example of the kind of user-land utility that is still best coded in C.
fetchmail does only the simplest kind of dynamic-memory management; its only complex data structure is a singly-linked list of per-mailserver control blocks built just once, at startup time, and changed only in fairly trivial ways afterwards. This substantially erodes the case against using C by sidestepping C's greatest weakness.
Finally, fetchmail requires the ability to parse a fairly complex specification syntax for per-mail-server control information. In the Unix world this sort of thing is classically handled by using C code generators that grind out source code for a tokenizer and grammar parser from declarative specifications. The existence of yacc and lex was a point in favor of C.
However, the real reason fetchmail is a C program is that it evolved by gradual mutation from an ancestor already written in C. The existing implementation has been extensively tested on many different platforms and against many odd and quirky servers. Carrying all that implicit knowledge through to a re-implementation in a different language would be messy and difficult. Furthermore, fetchmail depends on imported code for functions (like NTLM authentication) that don't seem to be available above C level.
fetchmail's interactive configurator, which did not have a C legacy problem, is written in Python; we'll discuss that case along with that language.
This has not happened. Part of the fault can be laid to problems in C++ itself; the requirement that it be backward-compatible with C forced a great many compromises on the design. Among other things, that requirement prevented C++ from going to fully automatic dynamic-memory management and addressing C's most serious problem. Later, feature arms races between different compiler implementers, unconstrained by a weak and premature standardization effort, pushed C++ to become rather baroque and excessively complicated.
It may be that C++'s realization of OO is particularly problem-prone. There is some evidence that C++ programs have higher life-cycle costs than equivalents in C, FORTRAN, or Ada. Whether this is a problem with OO or specifically with C++ or both remains unclear, though there is reason to suspect both are implicated [Hatton98].
In recent years, C++ has incorporated some important non-OO ideas. It has exceptions similar to those in Lisp; that is, it is possible to throw an object or value up the call stack until it is caught by a handler. STL (Standard Template Library) provides generic programming; that is, it is possible to code algorithms that are independent of the type signature of their data and have them compiled to do the right thing at runtime. (Only languages that do compile-time static type-checking need this; more dynamic languages simply pass around typeless references and support type identification at runtime.)
Efficient compiled language; upward-compatible with C; object-oriented platform; vehicle for cutting-edge techniques like STL and generics — C++ tries to be all things to all people, but the cost is more complexity than the mind of any individual programmer can handle. As we noted in Chapter═4, the language's principal designer has conceded that he doesn't expect any one programmer to grasp it all. Unix hackers do not react well to this; one anonymous but famous characterization is “C++: an octopus made by nailing extra legs onto a dog”.
When all is said and done, however, C++'s most fundamental problem is that it is basically just another conventional language. It confines the memory-management problem better than it did before the invention of the Standard Template Library, and a lot better than C does, but the confinement is brittle; it breaks unless your code uses objects and only objects. For many types of application its OO features are not significant, and simply add complexity to C without yielding much advantage. Open-source C++ compilers are available; if C++ were unequivocally superior to C it would now dominate.
Summing up: C++'s best side is its combination of compiled efficiency with facilities for OO and generic programming. Its worst side is that it is baroque and complex, and tends to encourage over-complex designs.
Consider using C++ if an existing C++ toolkit or service library offers powerful leverage for your application, or if you're in one of the application areas mentioned above for which an OO language is known to be a large win.
The classic C++ reference is Stroustrup's The C++ Programming Language [Stroustrup]. You will find an excellent beginner's tutorial on C++ and basic OO methods in C++: A Dialog [Heller]. C++ Annotations [Brokken] is a condensed introduction to C++ for expert C programmers.
The Gnu Compiler Collection includes a C++ compiler. The language is therefore universally available on Unix and on Microsoft operating systems; comments made under C above also apply here. Strong collections of open-source support libraries are available. However, portability is compromised by the fact that (as of mid-2003) actual C++ implementations implement widely varying subsets of the draft ISO standard now in preparation.
The Qt interface toolkit is one of the notable C++ success stories in today's open-source world. It provides a widget set and API for writing graphical user interfaces under X, one deliberately (and rather effectively) designed to emulate the visual look and feel of Motif, MacOS Platinum, or the Microsoft Windows interface. Qt actually provides more than just GUI services; it also provides a portable application layer, with classes for XML, file access, sockets, threads, timers, time/date handling, database access, various abstract data types, and Unicode.
The Qt toolkit is a critical and visible component of the KDE project, the senior of the open-source world's two efforts to produce a competitive GUI and integrated set of desktop productivity tools.
Qt's C++ implementation exhibits the strengths of an OO language for encapsulating user-interface components. In a language supporting objects, a visual hierarchy of interface widgets can be cleanly expressed in the code by a hierarchy of class instances. While this sort of thing can be simulated in C with explicit indirection through hand-rolled method tables, such code is much cleaner in C++. Comparison with the notoriously baroque C API of Motif is instructive.
The Qt source code and reference documentation are available at the Trolltech site.
Simple shell programs are extremely easy and natural to write. The Unix tradition of rapid prototyping in interpretive languages began with shell.
As program size gets larger, however, they tend to become rather ad-hoc. Some parts of shell syntax (notably its quoting and statement-syntax rules) can be very confusing. These drawbacks generally relate to compromises in the programming-language part of the shell's design made to preserve its utility as an interactive command-line interpreter.
Programs are described as being ‘in shell’ even when they are not pure shell but include heavy use of C filters like sort(1) and of standard text-processing minilanguages like sed(1) or awk(1). This sort of programming has been in decline for some years, however; nowadays such elaborate glue logic is generally written in Perl or Python, with shell being reserved for the simplest kinds of wrappers (for which these languages would be overkill) and system boot-time initialization scripts (which cannot assume they are available).
Such basic shell programming should be adequately covered in any introductory Unix book. The Unix Programming Environment [Kernighan-Pike84] remains one of the best sources on intermediate and advanced shell programming. Korn shell implementations or clones are present on every Unix.
Complex shellscripts often have portability problems, not so much because of the shell itself but because they make assumptions about what other programs are available as components. While Bourne and Korn-shell clones have been sporadically available on non-Unix operating systems, shell programs are not (practically speaking) at all portable off Unix.
Summing up: shell's best side is that it is very natural and quick for small scripts. Its worst side is that large shellscripts depend on lots of auxiliary commands that aren't necessarily identically behaved nor even present on all target machines. Nor is it easy to analyze the dependencies in a large shellscript.
It is almost never necessary to build or install a shell, since all Unix systems and Unix emulators come equipped with them. The standard shell on Linux and other leading-edge Unix variants is now bash.
Case Study: xmlto
xmlto handles the details
of calling an XSLT engine with appropriate stylesheet, then handing
off the result to a postprocessor. For HTML and XHTML the XSLT
transformation does the entire job. For plain text, the XML is also
processed into HTML, but then handed to a postprocessor —
-dump mode, which renders HTML to flat text.
For PostScript, the XML is transformed to XML FO (formatting
objects) which a
postprocessor then massages into TeX macros, to DVI format via
and then finally to PostScript via the well-known
xmlto consists of a single front-end shellscript. It calls any one of several script plugins, each named after the target format. Each plugin is a shellscript. Depending on how it's called, it either supplies a stylesheet for the front end to apply, or calls the appropriate postprocessor(s) with various canned arguments.
This architecture means that all the information about a given output format lives in one place (the corresponding script plugin), so adding new output types can be done without disturbing the front-end code at all.
xmlto is a good example of a medium-sized shell application. Neither C nor C++ would have made sense because they are awkward for scripting. Any of the other scripting languages in this chapter could have been used for this job; but it's all simple command dispatching, with no internal data structures or complex logic, so shell is good enough. Shell has the significant advantage of being ubiquitous on the intended target systems.
In theory this script could run on any system supporting bash. The real constraint is the requirement for one of the XSLT engines and all the postprocessors needed to be present on the system. In practice, this script is not likely to run anywhere but under one of the modern open-source Unixes.
Sorcerer GNU/Linux is a Linux distribution that you install as a small, bootable foothold system just powerful enough to run bash(1) and a couple of download utilities. With this code in place, you can invoke Sorcery, the Sorcerer package system.
Sorcery handles installing, removing, and integrity-checking software packages. When you “cast spells”, Sorcery downloads the source code, compiles it, installs it, and saves a list of files that were installed (along with a build log and checksums for all the files). Installed packages can be “dispelled” or removed. Package listing and integrity checks are also available. More details are available at the Sorcery project site.
The Sorcery system is written entirely in shell. Program installation procedures tend to be small, simple programs for which shell is appropriate. In this particular application, the main drawback of shell is neutralized because Sorcery's authors can guarantee that the helper programs they need will be present in the foothold system.
Perl's strongest point is its extremely powerful built-in facilities for pattern-directed processing of textual, line-oriented data formats; it is unsurpassed at this. It also includes far stronger data structures than shell, including dynamic arrays of mixed element types and a ‘hash’ or ‘dictionary’ type that supports convenient and fast lookup of name-value pairs.
Perl's main drawback is that parts of it are irredeemably ugly, complicated, and must be used with caution and in stereotyped ways lest they bite (its argument-passing conventions for functions are a good example of all three problems). It is harder to get started in Perl than it is in shell. Though small programs in Perl can be extremely powerful, careful discipline is required to maintain modularity and keep a design under control as program size increases. Because some limiting design decisions early in Perl's history could not be reversed, many of the more advanced features have a fragile, klugey feel about them.
The definitive reference on Perl is Programming Perl [Wall2000]. This book has nearly everything you will ever need to know in it, but is notoriously badly organized; you will have to dig to find what you want. A more introductory and narrative treatment is available in Learning Perl [Schwartz-Christiansen].
Perl is universal on Unix systems. Perl scripts at the same major release level tend to be readily portable between Unixes (provided they don't use extension modules). Perl implementations are available (and even well documented) for the Microsoft family of operating systems and on MacOS as well. Perl/Tk provides cross-platform GUI capability.
Summing up: Perl's best side is as a power tool for small glue scripts involving a lot of regular-expression grinding. Its worst side is that it is ugly, spiky, and nigh-unmaintainable in large volumes.
The blq script is a tool for querying block lists (lists of Internet sites that have been identified as habitual sources of unsolicited bulk email, aka spam). You can find current sources at the blq project page.
blq is a good example of a small Perl script, illustrating both the strengths and weaknesses of the language. It makes intensive use of regular-expression matching. On the other hand, the Net::DNS Perl extension module it uses has to be conditionally included, because it is not guaranteed to be present in any given Perl installation.
blq is exceptionally clean and disciplined as Perl code goes, and I recommend it as an example of good style (the other Perl tools referenced from the blq project page are good examples as well). But parts of the code are unreadable unless you are familiar with very specific Perl idioms — the very first line of code, $0 =~ s!.*/!!;, is an example. While all languages have some of this kind of opacity, Perl has it worse than most.
Tcl and Python are both good for small scripts of this type, but both lack the Perl convenience features for regular-expression matching that blq uses heavily; an implementation in either would have been reasonable, but probably less compact and expressive. An Emacs Lisp implementation would have been even faster to write and more compact than the Perl one, but probably painfully slow to use.
A Large Perl Case Study: keeper
keeper is the tool used to file incoming packages and maintain both FTP and WWW index files for the huge Linux free-software archives at ibiblio. You can find sources and documentation in the search tools subdirectory of the ibiblio archive.
keeper is a good example of a medium-to-large interactive Perl application. The command-line interface is line-oriented and patterned after a specialized shell or directory editor; note the embedded help facilities. The working parts make heavy use of file and directory handling, pattern matching, and pattern-directed editing. Note the ease with which keeper generates Web pages and electronic-mail notifications from programmatic templates. Note also the use of a canned Perl module to automate walking various functions over directory trees.
At about 3300 lines, this application is probably pushing the size and complexity limit of what one should attempt in a single Perl program. Nevertheless, most of it was written in a period of six days. In C, C++, or Java it would have taken a minimum of six weeks and been extremely difficult to debug or modify after the fact. It is way too large for pure Tcl. A Python version would probably be structurally cleaner, more readable, and more maintainable — but also more verbose (especially near the pattern-matching parts). An Emacs Lisp mode could readily do the job, but Emacs is not well suited for use over a telnet link that is often slowed to a crawl by server congestion.
Some facilities built on top of Tcl have achieved wide use outside the Tcl community itself. The two most important of these are:
- The Tk toolkit, a kinder and gentler X interface that makes it easy to rapidly build buttons, dialog boxes, menu trees, and scrolling text widgets and collect input from them.
- Expect, a language that makes it relatively easy to script fully interactive programs with widely variable responses.
The main advantage of Tcl itself is that it is extremely flexible and radically simple. The syntax is very odd (based on a positional parser) but totally consistent. There are no reserved words, and there is no syntactic distinction between a function call and ‘built in’ syntax; thus the Tcl language interpreter itself can be effectively redefined from within Tcl (which is what makes projects like Expect reasonable).
The oddities of the syntax can at first be a problem as well; the distinction between string quotes and braces will probably give you headaches for a while, and the rules for when things need to be quoted or braced are a bit tricky.
The Tcl world doesn't have one central repository run by a core group analogous to Perl's or Python's, but several excellent websites both point to each other and cover most Tcl tool and extension development. Look at the Tcl Developer Xchange first; among other things, it offers Tcl sources of an interactive Tcl tutorial. There is also a Tcl foundry at SourceForge.
Tcl scripts have portability problems similar to those of shell scripts; the language itself is highly portable, but the components it calls may not be. Tcl implementations exist for the Microsoft family of operating systems, MacOS, and many other platforms. Tcl/Tk scripts will run on any platform with GUI capabilities.
Summing up: Tcl's best side is its spare, compact design and the extensibility of the Tcl interpreter. Its worst side is the odd positional parser and the weakness of its data structures and namespace controls; the latter defect makes it scale poorly for large projects.
Case Study: TkMan
TkMan is a browser for Unix man pages and Texinfo documents. At roughly 1200 lines, it is quite large to be written in pure Tcl, but the code is unusually well-modularized and mature. It uses Tk to provide a GUI interface quite a bit nicer than either the stock man(1) or xman(1) utilities support.
TkMan makes a good case study because it exhibits almost the full gamut of Tcl techniques. Highlights include Tk integration, scripted control of other Unix applications (such as the Glimpse search engine), and the use of Tcl to parse Texinfo markup.
Any of the other languages would have made for a less direct interface to the Tk GUI that constitutes most of this code.
A Web search for “TkMan” should turn up sources and documentation.
The Moodss system is a graphical monitoring application for system administrators. It can watch logs and gather statistics for MySQL, Linux, SNMP networks, and Apache, and presents a digested view of them through spreadsheet-like GUI panels called ‘dashboards’. Monitoring modules can be written in Python or Perl as well as Tcl. The code is polished, mature, and considered an exemplar in the Tcl community. There is a project website.
The Moodss core consists of about 18,000 lines of Tcl. It uses several Tcl extensions including a custom object system; the Moodss author admits that without these “writing such a big application would not have been possible”.
Again, any of the other languages would have made for a less direct interface to the Tk GUI that constitutes most of this code.
The definitive Python reference is Programming Python [Lutz]. Extensive on-line documentation on Python extensions is also available at the Python website.
Python programs tend to be quite portable between Unixes and even across other operating systems; the standard library is powerful enough to significantly cut the use of nonportable helper programs. Python implementations are available for Microsoft operating systems and for MacOS. Cross-platform GUI development is possible with either Tk or two other toolkits. Python/C applications can be ‘frozen’, quasi-compiled into pure C sources that should be portable to systems with no Python installed.
Summing up: Python's best side is that it encourages clean, readable code and combines accessibility with scaling up well to large projects. Its worst side is inefficiency and slowness, not just relative to compiled languages but relative to other scripting languages as well.
A Small Python Case Study: imgsizer
Imgsizer is a utility that rewrites WWW pages so that image-inclusion tags get the right image size parameters automatically plugged in (this speeds up page loading on many browsers). You can find sources and documentation in the URL WWW tools subdirectory of the ibiblio archive.
imgsizer was originally written in Perl, and was a nearly ideal example of the sort of small, pattern-driven text-processing tool at which Perl excels. It was later translated to Python to take advantage of Python's library support for HTTP fetching; this eliminated a dependency on an external page-fetching utility. Observe the use of file(1) and ImageMagick identify(1) as specialist tools for extracting the pixel sizes of images.
The dynamic string handling and sophisticated regular-expression matching required would have made imgsizer quite painful to write in C or C++; that version would also have been much larger and harder to read. Java would have solved the implicit memory-management problem, but is hardly more expressive than C or C++ at text pattern matching.
A Medium-Sized Python Case Study: fetchmailconf
In Chapter═11 we examined the fetchmail/fetchmailconf pair as an example of one way to separate implementation from interface. Python's strengths are well illustrated by fetchmailconf.
fetchmailconf uses the Tk toolkit to implement a multi-panel GUI configuration editor (Python bindings also exist for GTK+ and other toolkits, but Tk bindings ship with every Python interpreter).
In expert mode, the GUI supports editing of about sixty attributes divided among three panel levels. Attribute widgets include a mix of checkboxes, radio buttons, text fields, and scrolling listboxes. Despite this complexity, the first fully-functional version of the configurator took me less than a week to design and code, counting the four days it took to learn Python and Tk.
Python excels at rapid prototyping of GUI interfaces, and (as fetchmailconf illustrates) such prototypes are often deliverable. Perl and Tcl have similar strengths in this area (including the Tk toolkit, which was written for Tcl) but are hard to control at the complexity level (approximately 1400 lines) of fetchmailconf. Emacs Lisp is not suited for GUI programming. Choosing Java would have increased the complexity overhead of this programming task without delivering significant benefits for this nonspeed-intensive application.
PIL, the Python Imaging Library, supports the manipulation of bitmap graphics. It supports many popular formats, including PNG, JPEG, BMP, TIFF, PPM, XBM, and GIF. Python programs can use it to convert and transform images; supported transformations include cropping, rotation, scaling, and shearing. Pixel editing, image convolution, and color-space conversions are also supported. The PIL distribution includes Python programs that make these library facilities available from the command line. Thus PIL can be used either for batch-mode image transformation or as a strong toolkit over which to implement program-driven image processing of bitmaps.
The implementation of PIL illustrates the way Python can be readily augmented with loadable object-code extensions to the Python interpreter. The library core, implementing fundamental operations on bitmap objects, is written in C for speed. The upper levels and sequencing logic are in Python, slower but much easier to read and modify and extend.
The analogous toolkit would be difficult or impossible to write in Emacs Lisp or shell, which don't have or don't document a C extension interface at all. Tcl has a good C extension facility, but PIL would be an uncomfortably large project in Tcl. Perl has such facilities (Perl XS), but they are ad-hoc, poorly documented, complex, and unstable by comparison to Python's and use of them is rare. Java's Native Method Interface appears to provide a facility roughly comparable to Python's; PIL would probably have made a reasonable Java project.
The PIL code and documentation is available at the project website.
There is a particularly invidious problem, resembling Windows
DLL hell, with libraries. Java has no method to manage
different library versions. This can create huge problems in
environments like application servers, where the server might come
equipped with one version of (say) an XML library, but the application
ships with a different (usually newer) version. The only handle on
such problems is the
CLASSPATH environment variable,
a source of chronic deployment problems.
Furthermore, Sun's handling of the Java language has been both politically and technically obtuse. Java's first GUI toolkit, AWT, was a mess that had to be essentially replaced. Withdrawing the language from ECMA/ISO standardization further nettled many developers already upset by features of the Sun Community Source License (SCSL). Restrictions in the SCSL continue to hamper open-source implementations of Java 1.2 and their J2EE (Java 2 Enterprise Edition) specification. This compromises Java's original objective of universal portability.
Sources for Kaffe, an open-source Java implementation with class libraries conforming to most of JDK 1.1 and portions of JDK 1.2, are available at the Kaffe project site.
There is a Java front end for GCC. GCJ can compile Java code to either Java bytecode or native code, and can compile Java bytecode to native code as well. It comes packaged with open-source class libraries that implement most of JDK 1.2, and a Java bytecode interpreter called gij. Details are at the GCJ project page.
There is a Java IDE for Emacs at the JDEE project site.
Java portability is excellent at the language level. Incomplete library implementations (especially older JDK 1.1 versions that don't support the newer JDK 1.2) can be an issue.
Java's best side is that it comes close enough to achieving write-once-run-anywhere to be useful as an OS-independent environment of its own. Its worst side is that the Java 1/Java 2 split compromises that goal in deeply frustrating ways.
Freenet is a peer-to-peer networking project that is intended to make censorship and content suppression impossible. Freenet developers envision the following applications:
- Uncensorable dissemination of controversial information: Freenet protects freedom of speech by enabling anonymous and uncensorable publication of material ranging from grassroots alternative journalism to banned exposИs.
- Efficient distribution of high-bandwidth content: Freenet's adaptive caching and mirroring is being used to distribute Debian Linux software updates.
- Universal personal publishing: Freenet enables anyone to have a website, without space restrictions or compulsory advertising, even if the would-be webmaster doesn't own a computer.
Freenet addresses these goals by providing a virtual space in which to publish documents that is not tied to any specific machine. Published information and Freenet's own internal data indexes are replicated and distributed across the network in such a way that even Freenet administrators don't know at any given time where all the physical copies are located. Privacy for people browsing or submitting to Freenet is protected by strong cryptography.
Java was a good choice for this project for at least two reasons. First: the goals of the project put a heavy premium on having compatible implementations on the widest possible variety of machines, so Java's high portability is a dominating advantage. Second: the nature of the project is such that the network API is important, and Java has a strong one built in.
C is traditional for infrastructure projects of this kind that have high performance demands, but the lack of a standardized network API would have made porting a significant difficulty. C++ would have had the same difficulty. Tcl, Perl, or Python might have reduced the porting burden, but at a greater cost in performance. Emacs Lisp would have been painfully slow and totally inappropriate.
Emacs Lisp is not a general-purpose language in quite the same way as the others surveyed in this chapter; while it is powerful enough to theoretically be used as such, it is traditionally employed only to write control programs for the Emacs editor itself and does not communicate as fluently with other software as would a modern scripting language.
More generally, Emacs is to pattern- or syntax-directed interactive editing what Perl is to pattern-directed batch editing. Any application that involves interactively hacking a special file format or text database is an excellent candidate to be prototyped (and possibly delivered) as an Emacs mode (an Emacs Lisp program that specializes the editor's behavior).
Emacs Lisp is also valuable for building applications that have to be closely integrated with a text editor, or that function primarily as text browsers with some editing capability. User agents for email and Usenet news fall in this category. So do certain kinds of database front ends.
Emacs Lisp is a Lisp. It follows as the night the day that it manages memory automatically and is far more elegant and powerful than most conventional languages, or indeed most unconventional languages; it can compete with Java or Python on this level and laugh at C or C++, Perl, shell or Tcl. Lisp's perennial problem of lacking a standardized OS binding for portability is solved by the Emacs core, which in effect is its OS binding.
Lisp's other perennial problem — being a resource hog — is no longer a real issue on modern machines. Parody expansions like ‘Emacs Makes A Computer Slow’ and ‘Eventually Munches All Computer Storage’ used to be common (in fact the Emacs distribution itself includes a list of them). But many other commonly used categories of programs (such as Web browsers) have nowadays grown larger and more complex than Emacs, which has come to appear rather moderate by comparison.
The definitive Emacs Lisp reference is The GNU Emacs Lisp Reference Manual, which may be browseable through your Emacs's ‘info’ help system. If not, it can be downloaded from the FSF FTP site. If you find that impenetrable, Writing GNU Emacs Extensions [Glickstein] may help.
Summing up: Emacs Lisp's best point is that it combines an excellent base language, Lisp, with powerful domain primitives for text manipulation. Its worst point is poor performance and difficulties using it in communication with other programs.
For more information, see the discussion of Emacs under editors in the next chapter.
Только зарегистрированные пользователи могут оценивать и комментировать статьи.