docstrip(n)                Literate programming tool               docstrip(n)



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NAME
       docstrip - Docstrip style source code extraction

SYNOPSIS
       package require Tcl  8.4

       package require docstrip  ?1.2?

       docstrip::extract text terminals ?option value ...?

       docstrip::sourcefrom filename terminals ?option value ...?

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DESCRIPTION
       Docstrip is a tool created to support a brand of Literate Programming.
       It is most common in the (La)TeX community, where it is being used for
       pretty much everything from the LaTeX core and up, but there is nothing
       about docstrip which prevents using it for other types of software.

       In short, the basic principle of literate programming is that program
       source should primarily be written and structured to suit the
       developers (and advanced users who want to peek "under the hood"), not
       to suit the whims of a compiler or corresponding source code consumer.
       This means literate sources often need some kind of "translation" to an
       illiterate form that dumb software can understand.  The docstrip Tcl
       package handles this translation.

       Even for those who do not whole-hartedly subscribe to the philosophy
       behind literate programming, docstrip can bring greater clarity to in
       particular:

       o      programs employing non-obvious mathematics

       o      projects where separate pieces of code, perhaps in different
              languages, need to be closely coordinated.

       The first is by providing access to much more powerful typographical
       features for source code comments than are possible in plain text.  The
       second is because all the separate pieces of code can be kept next to
       each other in the same source file.

       The way it works is that the programmer edits directly only one or
       several "master" source code files, from which docstrip generates the
       more traditional "source" files compilers or the like would expect. The
       master sources typically contain a large amount of documentation of the
       code, sometimes even in places where the code consumers would not allow
       any comments. The etymology of "docstrip" is that this documentation
       was stripped away (although "code extraction" might be a better
       description, as it has always been a matter of copying selected pieces
       of the master source rather than deleting text from it).  The docstrip
       Tcl package contains a reimplementation of the basic extraction
       functionality from the docstrip program, and thus makes it possible for
       a Tcl interpreter to read and interpret the master source files
       directly.

       Readers who are not previously familiar with docstrip but want to know
       more about it may consult the following sources.

       [1]    The tclldoc package and class, http://ctan.org/tex-
              archive/macros/latex/contrib/tclldoc/.

       [2]    The DocStrip utility, http://ctan.org/tex-
              archive/macros/latex/base/docstrip.dtx.

       [3]    The doc and shortvrb Packages, http://ctan.org/tex-
              archive/macros/latex/base/doc.dtx.

       [4]    Chapter 14 of The LaTeX Companion (second edition), Addison-
              Wesley, 2004; ISBN 0-201-36299-6.

FILE FORMAT
       The basic unit docstrip operates on are the lines of a master source
       file. Extraction consists of selecting some of these lines to be copied
       from input text to output text. The basic distinction is that between
       code lines (which are copied and do not begin with a percent character)
       and comment lines (which begin with a percent character and are not
       copied).


                 docstrip::extract [join {
                   {% comment}
                   {% more comment !"#$%&/(}
                   {some command}
                   { % blah $blah "Not a comment."}
                   {% abc; this is comment}
                   {# def; this is code}
                   {ghi}
                   {% jkl}
                 } \n] {}

       returns the same sequence of lines as


                 join {
                   {some command}
                   { % blah $blah "Not a comment."}
                   {# def; this is code}
                   {ghi} ""
                 } \n

       It does not matter to docstrip what format is used for the
       documentation in the comment lines, but in order to do better than
       plain text comments, one typically uses some markup language. Most
       commonly LaTeX is used, as that is a very established standard and also
       provides the best support for mathematical formulae, but the
       docstrip::util package also gives some support for doctools-like
       markup.

       Besides the basic code and comment lines, there are also guard lines,
       which begin with the two characters '%<', and meta-comment lines, which
       begin with the two characters '%%'. Within guard lines there is
       furthermore the distinction between verbatim guard lines, which begin
       with '%<<', and ordinary guard lines, where the '%<' is not followed by
       another '<'. The last category is by far the most common.

       Ordinary guard lines conditions extraction of the code line(s) they
       guard by the value of a boolean expression; the guarded block of code
       lines will only be included if the expression evaluates to true.  The
       syntax of an ordinary guard line is one of


                  '%' '<' STARSLASH EXPRESSION '>'
                  '%' '<' PLUSMINUS EXPRESSION '>' CODE

       where


                  STARSLASH  ::=  '*' | '/'
                  PLUSMINUS  ::=  | '+' | '-'
                  EXPRESSION ::= SECONDARY | SECONDARY ',' EXPRESSION
                               | SECONDARY '|' EXPRESSION
                  SECONDARY  ::= PRIMARY | PRIMARY '&' SECONDARY
                  PRIMARY    ::= TERMINAL | '!' PRIMARY | '(' EXPRESSION ')'
                  CODE       ::= { any character except end-of-line }

       Comma and vertical bar both denote 'or'. Ampersand denotes 'and'.
       Exclamation mark denotes 'not'. A TERMINAL can be any nonempty string
       of characters not containing '>', '&', '|', comma, '(', or ')',
       although the docstrip manual is a bit restrictive and only guarantees
       proper operation for strings of letters (although even the LaTeX core
       sources make heavy use also of digits in TERMINALs).  The second
       argument of docstrip::extract is the list of those TERMINALs that
       should count as having the value 'true'; all other TERMINALs count as
       being 'false' when guard expressions are evaluated.

       In the case of a '%<*EXPRESSION>' guard, the lines guarded are all
       lines up to the next '%</EXPRESSION>' guard with the same EXPRESSION
       (compared as strings). The blocks of code delimited by such '*' and '/'
       guard lines must be properly nested.


                 set text [join {
                    {begin}
                    {%<*foo>}
                    {1}
                    {%<*bar>}
                    {2}
                    {%</bar>}
                    {%<*!bar>}
                    {3}
                    {%</!bar>}
                    {4}
                    {%</foo>}
                    {5}
                    {%<*bar>}
                    {6}
                    {%</bar>}
                    {end}
                 } \n]
                 set res [docstrip::extract $text foo]
                 append res [docstrip::extract $text {foo bar}]
                 append res [docstrip::extract $text bar]

       sets $res to the result of


                 join {
                    {begin}
                    {1}
                    {3}
                    {4}
                    {5}
                    {end}
                    {begin}
                    {1}
                    {2}
                    {4}
                    {5}
                    {6}
                    {end}
                    {begin}
                    {5}
                    {6}
                    {end} ""
                 } \n

       In guard lines without a '*', '/', '+', or '-' modifier after the '%<',
       the guard applies only to the CODE following the '>' on that single
       line. A '+' modifier is equivalent to no modifier. A '-' modifier is
       like the case with no modifier, but the expression is implicitly
       negated, i.e., the CODE of a '%<-' guard line is only included if the
       expression evaluates to false.

       Metacomment lines are "comment lines which should not be stripped
       away", but be extracted like code lines; these are sometimes used for
       copyright notices and similar material. The '%%' prefix is however not
       kept, but substituted by the current -metaprefix, which is customarily
       set to some "comment until end of line" character (or character
       sequence) of the language of the code being extracted.


                 set text [join {
                    {begin}
                    {%<foo> foo}
                    {%<+foo>plusfoo}
                    {%<-foo>minusfoo}
                    {middle}
                    {%% some metacomment}
                    {%<*foo>}
                    {%%another metacomment}
                    {%</foo>}
                    {end}
                 } \n]
                 set res [docstrip::extract $text foo -metaprefix {# }]
                 append res [docstrip::extract $text bar -metaprefix {#}]

       sets $res to the result of


                 join {
                    {begin}
                    { foo}
                    {plusfoo}
                    {middle}
                    {#  some metacomment}
                    {# another metacomment}
                    {end}
                    {begin}
                    {minusfoo}
                    {middle}
                    {# some metacomment}
                    {end} ""
                 } \n

       Verbatim guards can be used to force code line interpretation of a
       block of lines even if some of them happen to look like any other type
       of lines to docstrip. A verbatim guard has the form '%<<END-TAG' and
       the verbatim block is terminated by the first line that is exactly
       '%END-TAG'.


                 set text [join {
                    {begin}
                    {%<*myblock>}
                    {some stupid()}
                    {   #computer<program>}
                    {%<<QQQ-98765}
                    {% These three lines are copied verbatim (including percents}
                    {%% even if -metaprefix is something different than %%).}
                    {%</myblock>}
                    {%QQQ-98765}
                    {   using*strange@programming<language>}
                    {%</myblock>}
                    {end}
                 } \n]
                 set res [docstrip::extract $text myblock -metaprefix {# }]
                 append res [docstrip::extract $text {}]

       sets $res to the result of


                 join {
                    {begin}
                    {some stupid()}
                    {   #computer<program>}
                    {% These three lines are copied verbatim (including percents}
                    {%% even if -metaprefix is something different than %%).}
                    {%</myblock>}
                    {   using*strange@programming<language>}
                    {end}
                    {begin}
                    {end} ""
                 } \n

       The processing of verbatim guards takes place also inside blocks of
       lines which due to some outer block guard will not be copied.

       The final piece of docstrip syntax is that extraction stops at a line
       that is exactly "\endinput"; this is often used to avoid copying random
       whitespace at the end of a file. In the unlikely case that one wants
       such a code line, one can protect it with a verbatim guard.

COMMANDS
       The package defines two commands.

       docstrip::extract text terminals ?option value ...?
              The extract command docstrips the text and returns the extracted
              lines of code, as a string with each line terminated with a
              newline. The terminals is the list of those guard expression
              terminals which should evaluate to true.  The available options
              are:

              -annotate lines
                     Requests the specified number of lines of annotation to
                     follow each extracted line in the result. Defaults to 0.
                     Annotation lines are mostly useful when the extracted
                     lines are to undergo some further transformation. A first
                     annotation line is a list of three elements: line type,
                     prefix removed in extraction, and prefix inserted in
                     extraction. The line type is one of: 'V' (verbatim), 'M'
                     (metacomment), '+' (+ or no modifier guard line), '-' (-
                     modifier guard line), '.' (normal line). A second
                     annotation line is the source line number. A third
                     annotation line is the current stack of block guards.
                     Requesting more than three lines of annotation is
                     currently not supported.

              -metaprefix string
                     The string by which the '%%' prefix of a metacomment line
                     will be replaced. Defaults to '%%'. For Tcl code this
                     would typically be '#'.

              -onerror keyword
                     Controls what will be done when a format error in the
                     text being processed is detected. The settings are:

                     ignore Just ignore the error; continue as if nothing
                            happened.

                     puts   Write an error message to stderr, then continue
                            processing.

                     throw  Throw an error. The -errorcode is set to a list
                            whose first element is DOCSTRIP, second element is
                            the type of error, and third element is the line
                            number where the error is detected. This is the
                            default.

              -trimlines boolean
                     Controls whether spaces at the end of a line should be
                     trimmed away before the line is processed. Defaults to
                     true.

              It should be remarked that the terminals are often called
              "options" in the context of the docstrip program, since these
              specify which optional code fragments should be included.

       docstrip::sourcefrom filename terminals ?option value ...?
              The sourcefrom command is a docstripping emulation of source. It
              opens the file filename, reads it, closes it, docstrips the
              contents as specified by the terminals, and evaluates the result
              in the local context of the caller, during which time the info
              script value will be the filename. The options are passed on to
              fconfigure to configure the file before its contents are read.
              The -metaprefix is set to '#', all other extract options have
              their default values.

DOCUMENT STRUCTURE
       The file format (as described above) determines whether a master source
       code file can be processed correctly by docstrip, but the usefulness of
       the format is to no little part also dependent on that the code and
       comment lines together constitute a well-formed document.

       For a document format that does not require any non-Tcl software, see
       the ddt2man command in the docstrip::util package. It is suggested that
       files employing that document format are given the suffix ".ddt", to
       distinguish them from the more traditional LaTeX-based ".dtx" files.

       Master source files with ".dtx" extension are usually set up so that
       they can be typeset directly by latex without any support from other
       files. This is achieved by beginning the file with the lines


                 % \iffalse
                 %<*driver>
                 \documentclass{tclldoc}
                 \begin{document}
                 \DocInput{filename.dtx}
                 \end{document}
                 %</driver>
                 % \fi

       or some variation thereof. The trick is that the file gets read twice.
       With normal LaTeX reading rules, the first two lines are comments and
       therefore ignored. The third line is the document preamble, the fourth
       line begins the document body, and the sixth line ends the document, so
       LaTeX stops there ? non-comments below that point in the file are never
       subjected to the normal LaTeX reading rules. Before that, however, the
       \DocInput command on the fifth line is processed, and that does two
       things: it changes the interpretation of '%' from "comment" to
       "ignored", and it inputs the file specified in the argument (which is
       normally the name of the file the command is in).  It is this second
       time that the file is being read that the comments and code in it are
       typeset.

       The function of the \iffalse ... \fi is to skip lines two to seven on
       this second time through; this is similar to the "if 0 { ... }" idiom
       for block comments in Tcl code, and it is needed here because (amongst
       other things) the \documentclass command may only be executed once. The
       function of the <driver> guards is to prevent this short piece of LaTeX
       code from being extracted by docstrip.  The total effect is that the
       file can function both as a LaTeX document and as a docstrip master
       source code file.

       It is not necessary to use the tclldoc document class, but that does
       provide a number of features that are convenient for ".dtx" files
       containing Tcl code. More information on this matter can be found in
       the references above.

SEE ALSO
       docstrip_util

KEYWORDS
CATEGORY
       Documentation tools

COPYRIGHT
       Copyright (c) 2003?2010 Lars Hellstrom <Lars dot Hellstrom at residenset dot net>




docstrip                              1.2                          docstrip(n)
