[manpage_begin rcs n 0.2]
[see_also struct]
[see_also textutil]
[keywords CVS]
[keywords {diff -n format}]
[keywords patching]
[keywords RCS]
[keywords {RCS patch}]
[keywords SCCS]
[keywords {text conversion}]
[keywords {text differences}]
[moddesc {RCS low level utilities}]
[copyright {2005, Andreas Kupries <andreas_kupries@users.sourceforge.net>}]
[copyright {2005, Colin McCormack <coldstore@users.sourceforge.net>}]
[titledesc {RCS low level utilities}]
[category  {Text processing}]
[require Tcl "8.5 9"]
[require rcs [opt 0.2]]
[description]
[para]

The [term {Revision Control System}], short [term RCS], is a set of
applications and related data formats which allow a system to persist
the history of changes to a text. It, and its relative SCCS are the
basis for many other such systems, like [term CVS], etc.

[para]

This package [emph {does not}] implement RCS.

[para]

It only provides a number of low level commands which should be useful
in the implementation of any revision management system, namely:

[list_begin enumerated]
[enum]

The conversion of texts into and out of a data structures which allow
the easy modification of such text by [term patches], i.e. sequences
of instructions for the transformation of one text into an other.

[enum]

And the conversion of one particular format for patches, the so-called
[term {RCS patches}], into and out of data structures which allow
their easy application to texts.

[list_end]
[comment {
	In the future we might add the generation and decoding
	of other patch formats as well. Like regular 'patch'
	patches, or also context and unified patches.
}]

[section {COMMANDS}]

[list_begin definitions]

[call [cmd ::rcs::text2dict] [arg text]]

Converts the argument [arg text] into a dictionary containing and
representing the same text in an indexed form and returns that
dictionary as its result.

More information about the format of the result can be found in
section [sectref {TEXT DICT DATA STRUCTURE}]. This command returns the
[term canonical] representation of the input.

[call [cmd ::rcs::dict2text] [arg dict]]

This command provides the complementary operation to

[cmd ::rcs::text2dict]. It converts a dictionary in the form described
in section [sectref {TEXT DICT DATA STRUCTURE}] back into a text and
returns that text as its result. The command does accept non-canonical
representations of the text as its input.

[call [cmd ::rcs::file2dict] [arg filename]]

This command is identical to [cmd ::rcs::text2dict], except that it
reads the text to convert from the file with path [arg filename]. The
file has to exist and must be readable as well.

[call [cmd ::rcs::dict2file] [arg filename] [arg dict]]

This command is identical to [cmd ::rcs::2dict2text], except that it
stores the resulting text in the file with path [arg filename]. The
file is created if it did not exist, and must be writable. The result
of the command is the empty string.

[call [cmd ::rcs::decodeRcsPatch] [arg text]]

Converts the [arg text] argument into a patch command list (PCL) as
specified in the section [sectref {RCS PATCH COMMAND LIST}] and
returns this list as its result.

It is assumed that the input text is in [term {diff -n format}], also
known as [term {RCS patch}] format, as specified in the section
[sectref rpf].

Please note that the command ignores no-ops in the input, in other
words the resulting PCL contains only instructions doing something.

[call [cmd ::rcs::encodeRcsPatch] [arg pcmds]]

This command provides the complementary operation to

[cmd ::rcs::decodeRcsPatch]. It convert a patch comand list (PCL) list
as specified in the section [sectref {RCS PATCH COMMAND LIST}] back
into a text in [sectref rpf] and returns that text as its result.

[para]

Note that this command and [cmd ::rcs::decodeRcsPatch] are not exactly
complementary, as the latter strips no-ops from its input, which the
encoder cannot put back anymore into the generated RCS patch. In other
words, the result of a decode/encode step may not match the original
input at the character level, but it will match it at the functional
level.

[call [cmd ::rcs::applyRcsPatch] [arg text] [arg pcmds]]

This operation applies a patch in the form of a PCL to a text given in
the form of a dictionary and returns the modified text, again as
dictionary, as its result.

[para]

To handle actual text use the commands [cmd ::rcs::text2dict] (or
equivalent) and [cmd ::rcs::decodeRcsPatch] to transform the inputs
into data structures acceptable to this command. Analogously use the
command [cmd ::rcs::dict2text] (or equivalent) to transform the
result of this command into actuall text as required.

[list_end]

[section {TEXT DICT DATA STRUCTURE}]

A text dictionary is a dictionary whose keys are integer numbers and
text strings as the associated values. The keys represent the line
numbers of a text and the values the text of that line.  Note that one
text can have many representations as a dictionary, as the index
values only have to be properly ordered for reconstruction, their
exact values do not matter. Similarly the strings may actually span
multiple physical lines.

[para]

The text

[para]
[example {Hello World,
how are you ?
Fine, and you ?}]
[para]

for example can be represented by

[para]
[example {{{1 {Hello World,}} {2 {how are you ?}} {3 {Fine, and you ?}}}}]
[para]

or

[para]
[example {{{5 {Hello World,}} {8 {how are you ?}} {9 {Fine, and you ?}}}}]
[para]

or

[para]
[example {{{-1 {Hello World,
how are you ?}} {4 {Fine, and you ?}}}}]
[para]

The first dictionary is the [term canonical] representation of the
text, with line numbers starting at [const 1], increasing in steps of
[const 1] and without gaps, and each value representing exactly one
physical line.

[para]

All the commands creating dictionaries from text will return the
canonical representation of their input text. The commands taking a
dictionary and returning text will generally accept all
representations, canonical or not.

[para]

The result of applying a patch to a text dictionary will in general
cause the dictionary to become non-canonical.

[section {RCS PATCH FORMAT} rpf]

A [term patch] is in general a series of instructions how to transform
an input text T into a different text T', and also encoded in text
form as well.

[para]

The text format for patches understood by this package is a very
simple one, known under the names [term {RCS patch}] or

[term {diff -n format}].

[para]

Patches in this format contain only two different commands, for the
deletion of old text, and addition of new text. The replacement of
some text by a different text is handled as combination of a deletion
following by an addition.

[para]

The format is line oriented, with each line containing either a
command or text data associated with the preceding command.

The first line of a [term {RCS patch}] is always a command line.

[para]
The commands are:

[list_begin definitions]
[def "\"\""]

The empty line is a command which does nothing.

[def "\"a[var start] [var n]\""]

A line starting with the character [const a] is a command for the
addition of text to the output. It is followed by [var n] lines of
text data. When applying the patch the data is added just between the
lines [var start] and [var start]+1. The same effect is had by
appending the data to the existing text on line [var start]. A
non-existing line [var start] is created.

[def "\"d[var start] [var n]\""]

A line starting with the character [const d] is a command for the
deletion of text from the output. When applied it deletes [var n]
lines of text, and the first line deleted is at index [var start].

[list_end]

Note that the line indices [var start] always refer to the text which
is transformed as it is in its original state, without taking the
precending changes into account.

[para]

Note also that the instruction have to be applied in the order they
occur in the patch, or in a manner which produces the same result as
in-order application.

[para]

This is the format of results returned by the command
[cmd ::rcs::decodeRcsPatch] and accepted by the commands
[cmd ::rcs::encodeRcsPatch] and [cmd ::rcs::appplyRcsPatch]
resp.

Note however that the decoder will strip no-op commands, and the
encoder will not generate no-ops, making them not fully complementary
at the textual level, only at the functional level.

[para]

And example of a RCS patch is

[para]
[example {d1 2
d4 1
a4 2
The named is the mother of all things.

a11 3
They both may be called deep and profound.
Deeper and more profound,
The door of all subtleties!}]

[section {RCS PATCH COMMAND LIST}]

Patch command lists (sort: PCL's) are the data structures generated by
patch decoder command and accepted by the patch encoder and applicator
commands. They represent RCS patches in the form of Tcl data
structures.

[para]

A PCL is a list where each element represents a single patch
instruction, either an addition, or a deletion. The elements are lists
themselves, where the first item specifies the command and the
remainder represent the arguments of the command.

[list_begin definitions]
[def a]

This is the instruction for the addition of text. It has two
arguments, the index of the line where to add the text, and the text
to add, in this order.

[def d]

This is the instruction for the deletion of text. It has two
arguments, the index of the line where to start deleting text, and the
number of lines to delete, in this order.

[list_end]

[para]

This is the format returned by the patch decoder command and accepted
as input by the patch encoder and applicator commands.

[para]

An example for a patch command is shown below, it represents the
example RCS patch found in section [sectref rpf].

[para]
[example {{{d 1 2} {d 4 1} {a 4 {The named is the mother of all things.

}} {a 11 {They both may be called deep and profound.
Deeper and more profound,
The door of all subtleties!}}}}]

[vset CATEGORY rcs]
[include ../common-text/feedback.inc]
[manpage_end]
