-*- outline -*- * Copyright (C) 2010, 2011 Didier Verna This file is part of Clon. Copying and distribution of this file, with or without modification, are permitted in any medium without royalty provided the copyright notice and this notice are preserved. * Introduction In the Lisp family of languages, one of the key components is the so-called REPL, the Read-Eval-Print Loop, which blends the runtime, compilation and development phases together, allowing for a very high level of interaction with the program. The importance of this paradigm explains why it is still rare to find "standalone" applications written in Lisp: most Lisp application clients are lispers themselves, and they prefer to live in the REPL. On the other hand, many contemporary Common Lisp compilers provide ways of creating standalone Common Lisp programs, using either shebang technology or by directly dumping executables. This process is getting easier to achieve every day. For instance, with SBCL, all it takes is one function call (save-lisp-and-die) and one command-line option to the compiler (--script). The (big) size of a Lisp image has been considered a showstopper in creating standalone applications for a long time, but nowadays, it doesn't really matter anymore (if you are not convinced, just figure out the average size of an application bundle under Mac OS X). This, along with the fact that Common Lisp compilers can generate very efficient code today, makes the perspective of standalone Common Lisp applications very tempting again. When it comes to preserving interaction with the user, one of the key components in a standalone application is the handling of the command-line. Clon is a library designed to do just that. * Overview Clon provides traditional features one might expect from a command-line options management library, but what makes it somewhat unique in its conception is that it has been designed with both the application developer and the application user in mind: many aspects of the command-line management usually imposed by the program are in fact under the control of the application user. The idea is that all Clon-enabled applications behave in a uniform way, and that it is the user who gets to decide, not the developper. The most important features of Clon are listed below. ** Command-Line Syntax Clon imposes a particular yet flexible syntax for the command-line. Options have short and/or long names, beginning with either one or two dashes. Options may take an argument. In that case, the argument may be optional or mandatory. Option names may be abbreviated and one-character options may be grouped together in a single call. There is an additional call syntax for Boolean or Boolean-based options. Finally, the command-line may have a "postfix", that is, a non-option part. ** Option Types Clon comes with a set of predefined option types, including "flags" (option without arguments), "switches" (Boolean options), simple Lisp objects, simple strings, enumerations, pathnames etc. Clon is also extensible: it is possible to define new option types, either from scratch or by subclassing an existing one. ** Value Retrieval The traditional approach to command-line analysis is to process it sequentially, and Clon lets you do that. However, Clon also provides an explicit retrieval mechanism by which you can directly request the value of a specific option, regardless of its position, or even its presence on the command-line. An option's value can be retrieved from different sources: a command-line argument, a "fallback" value (for optional arguments), a default value or an environment variable associated with the option. The retrieval process is completely automated, hence removing this burden from the developer's shoulders. ** Error Management Another cumbersome task already taken care of is error management. Clon provides two built-in error management schemes, in case something is wrong on the command-line. The simplest one is to quit the application with an informative error message. The other one is to enter an interactive dialog with the user, in which it is possible to fix the problem (correct a typo, discard an option call, provide a missing argument or value etc.). A unique feature of Clon is that the application user may choose his or her preferred error management scheme. ** Help String Contents The "help string" is typically what you expect from the output of a --help option. Maintaining an up-to-date help string is a very boring task, so Clon completely automates this for you (another burden removed from the developer's shoulders). However, the application programmer still has control over the help string's contents, notably the order in which options are displayed, and also by having the possibility of grouping options together and inserting arbitrary text in the output. ** Help String Format Clon also completely automates the help string typesetting process. For instance, it can automatically format the output for 80 columns, but it is also aware of the tty geometry and will use it when appropriate. Clon also supports help string "fontification" (or "highlighting") through ISO/IEC 6429 SGR escape sequences on tty's that support it. Another unique feature of Clon is that the exact format and highlight specification for the help string is under the control of the application user, via the notion of "theme". Clon comes with a set of predefined themes (for instance, standard, with heavy fontification, refcard for quick reference etc.) and application users can define their own. As a matter of fact, a theme not only controls the format and highlight of the help string, but also its contents.