CSE320/hw2/doc/par.1

.\"*********************
.\"* par.1             *
.\"* for Par 3.20      *
.\"* Copyright 1993 by *
.\"* Adam M. Costello  *
.\"*********************
.\"
.\" This is nroff -man (or troff -man) code.
.\"
.TH par 1 "1993" "Par 3.20" "USER COMMANDS"
.SH NAME
par \- filter for reformatting paragraphs
.SH SYNOPSIS
.ds O \fR[\fP
.ds C \fR]\fP
.de OP
.BI \*O\ \\$1 \\$2\ \*C
..
.HP
.na
.B par
.OP w width
.OP p prefix
.OP s suffix
.OP h \*Ohang\*C
.OP l \*Olast\*C
.OP m \*Omin\*C
.OP version
.ad
.LP 0.5i
Any option may be immediately
preceeded by a minus sign (\-).
.ie t .ds Q ``
.el .ds Q ""
.ie t .ds U ''
.el .ds U ""
.SH DESCRIPTION
.de IT
.LP
\h'-\w"\\$1\ "u'\\$1\ \\$2 \\$3 \\$4 \\$5 \\$6 \\$7 \\$8 \\$9
..
.LP
.B par
is a filter which copies its input to
its output, reformatting each paragraph.
Paragraphs are delimited by blank lines.
.LP
Each output paragraph is generated from
the corresponding input lines as follows:
.RS
.LP
.IT 1. An optional prefix and/or suffix
is removed from each input line.
.IT 2. The remainder is divided into
words (delimited by white space).
.IT 3. The words are joined into lines
to make an eye-pleasing paragraph.
.IT 4. The prefixes and suffixes are reattached.
.SH OPTIONS
.LP
All options except
.B version
are used to set values of variables. Values set by
command line options hold for all paragraphs in the
input. Unset variables are given default values
which are recomputed separately for each paragraph.
.LP
The approximate role of each
variable is described here. See the
.SM DETAILS
section for a much more complete and precise description.
.TP 1i
.BI w width
Sets the value of
.IR width,
the maximum width of the output paragraph, in characters,
not including the trailing newline characters.
Must be an unsigned decimal integer greater than
.I prefix
(see below). Defaults to 72. If
.I width
is 9 or more, the
.B w
is not needed.
.TP
.BI p prefix
Sets the value of
.IR prefix ,
the length of the prefix, in characters. Must be an unsigned
decimal integer. Defaults to 0 if there are no more than
.I hang
+ 1 lines in the input paragraph (see the
.B h
option). Otherwise defaults to the length
of the longest common prefix of all lines
in the input paragraph except the first
.I hang
of them. The first
.I prefix
characters of each output line are copied from the first
.I prefix
characters of the corresponding input line. If
.I prefix
is 8 or less, the
.B p
is not needed.
.TP
.BI s suffix
Sets the value of
.IR suffix ,
the length of the suffix, in characters. Must be an unsigned
decimal integer. Defaults to 0 if there is no more than
1 line in the input paragraph. Otherwise defaults to the
length of the longest common suffix of all lines in the
input paragraph, after this common suffix has been stripped
of all initial white characters save the last. The last
.I suffix
characters of each output line are copied from the last
.I suffix
characters of the corresponding input line.
.TP
.BI h\fR[ hang\fR]
Sets the value of
.IR hang .
Must be an unsigned decimal integer. Defaults
to 0. Mainly affects the default value of
.I prefix
(see the
.B p
option). If the
.B h
option is given without a number, the value 1 is assumed.
.TP
.BI l\fR[ last\fR]
Sets the value of
.IR last .
Must be 0 or 1. Defaults to 0. If
.I last
is 1,
.B par
tries to make the last line of the output paragraph
about the same length as the others. If the l option
is given without a number, the value 1 is assumed.
.TP
.BI m\fR[ min\fR]
Sets the value of
.IR min .
Must be 0 or 1. Defaults to
.IR last .
If
.I min
is 1,
.B par
will try to make the paragraph narrower
without shortening the shortest line. If the
.B m
option is given without a number, the value 1 is assumed.
.TP
.B version
Causes all other options to be ignored. No input is
read. \*Qpar 3.20\*U is printed on the output. Of
course, this will change in future releases of Par.
.LP 0.5i
If the value of any variable is set more than
once, the last value is used. For each paragraph,
default values for any variables not set by command
line options are computed in the following order:
.RS
.LP
.I width hang last min prefix suffix
.RE
.LP
No integer appearing in an option may exceed 9999.
.LP
It is an error if
.I width
<=
.I prefix
+
.IR suffix .
.SH ENVIRONMENT
.LP
If the environment variable
.SM PARINIT
is set,
.B par
will read command line options from it
before it reads them from the command line.
.SH DETAILS
.LP
The white characters are the space, formfeed,
newline, carriage return, tab, and vertical tab.
.LP
Lines are terminated by newline characters, but the
newlines are not considered to be included in the lines.
If the last character of the input is a non-newline,
then a newline will be inferred immediately after
it (but if the input is empty, no newline will be
inferred; the number of input lines will be 0). Thus,
the input can always be viewed as a sequence of lines.
.LP
A line is called
.I blank
if and only if it contains no non-white characters.
A subsequence of non-blank lines is called
.I maximal
if and only if there is no non-blank
line immediately before or after it.
.LP
The process described in the remainder of this section
is applied independently to each maximal subsequence of
non-blank input lines. (Each blank line of the input
is transformed into an empty line on the output).
.LP
After the values of the variables are determined (see the
.SM OPTIONS
section), the first
.I prefix
characters and the last
.I suffix
characters of each input line are removed and remembered.
It is an error for any line to contain fewer than
.I prefix
+
.I suffix
characters.
.LP
The remaining text is treated as a sequence of
characters, not lines. The text is broken into words,
which are delimited by white characters. That is, a
.I word
is a maximal sub-sequence of non-white characters. If there
is at least one word, and the first word is preceeded only
by spaces (strictly spaces, not other white characters),
then the first word is expanded to include those spaces.
.LP
Let
.I L
=
.I width
\-
.I prefix
\-
.IR suffix .
.LP
Every word which contains more than
.I L
characters is broken, after each
.IR L th
character, into multiple words.
.LP
These words are reassembled, preserving their
order, into lines. Adjacent words within
a line are separated by a single space.
.LP
If all the words fit on a single line of no more than
.I L
characters, then no line breaks are inserted. Otherwise,
line breaks are placed in such a way that the
resulting paragraph satisfies certain properties. If
.I min
is 1, those properties are:
.RS
.LP
.IT 1. No line contains more than
.I L
characters.
.IT 2. The shortest line is as
long as possible, subject to 1.
.IT 3. The longest line is as short as possible,
subject to properties 1 and 2. Call its length
.IR newL .
.IT 4. The sum of the squares
of the differences between
.I newL
and the lengths of the lines is as small as
possible, subject to properties 1, 2, and 3.
.RE
.LP
If
.I last
is 0, then the last line does not count as a line
for the purposes of properties 2 and 4 above.
.LP
If
.I min
is 0, then property 3 is disregarded, and
.I newL
is set equal to
.IR L .
.LP
If the number of lines in the
resultant paragraph is less than
.IR hang ,
then empty lines are added at the end
to bring the number of lines up to
.IR hang .
.LP
If
.I suffix
is not 0, then each line is padded at the
end with spaces to bring its length up to
.IR newL .
.LP
To each line is prepended
.I prefix
characters. Let
.I n
be the number of input lines. The
characters which are prepended to the
.IR i th
line are chosen as follows:
.RS
.LP
.IT 1. If
.I i
<=
.IR n ,
then the characters are copied from the ones
that were removed from the beginning of the
.IR n th
input line.
.IT 2. If
.I i
>
.I n
>
.IR hang ,
then the characters are copied from the ones that were
removed from the beginning of the last input line.
.IT 3. If
.I i
>
.I n
and
.I n
<=
.IR hang ,
then the characters are all spaces.
.RE
.LP
Then to each line is appended
.I suffix
characters. The characters which are appended to the
.IR i th
line are chosen as follows:
.RS
.LP
.IT 1. If
.I i
<=
.IR n ,
then the characters are copied from the
ones that were removed from the end of the
.IR n th
input line.
.IT 2. If
.I i
>
.I n
> 0, then the characters are copied from the ones that
were removed from the end of the last input line.
.IT 3. If
.I n
= 0, then the characters are all spaces.
.RE
.LP
Finally, the lines are printed to the output.
.SH DIAGNOSTICS
.LP
If there are no errors,
.B par
returns
.SM EXIT_SUCCESS
(see
.BR <stdlib.h> ).
.LP
If there is an error, then an error
message will be printed to the output, and
.B par
will return
.SM EXIT_FAILURE\s0\.
If the error is local to a single paragraph, then the
preceeding paragraphs will have been output before the
error was detected. Line numbers in error messages are
local to the input paragraph in which the error occurred.
.LP
Of course, trying to print an error message would be
futile if an error resulted from an output function, so
.B par
doesn't bother doing any error checking on output functions.
.SH EXAMPLES
.de VS
.RS -0.5i
.LP
.nf
.ps -1
.cs R 20
..
.de VE
.cs R
.ps
.fi
.RE
..
.de CM
\&\*Q\fB\\$1\fP\\*U:
..
.LP
The superiority of
.BR par 's
dynamic programming algorithm over a
greedy algorithm (such as the one used by
.BR fmt )
can be seen in the following example:
.LP
Original paragraph (note that
each line begins with 8 spaces):
.VS
        We hold these truths to be self evident,
        that all men are created equal,
        that they are endowed by their creator
        with certain unalienable rights,
        that among these are
        life, liberty, and the
        pursuit of happiness.
.VE
.LP
After a greedy algorithm with width = 61:
.VS
        We hold these truths to be self evident, that all men
        are created equal, that they are endowed by their
        creator with certain unalienable rights, that among
        these are life, liberty, and the pursuit of
        happiness.
.VE
.LP
After
.CM "par 61"
.VS
        We hold these truths to be self evident, that all
        men are created equal, that they are endowed by
        their creator with certain unalienable rights, that
        among these are life, liberty, and the pursuit of
        happiness.
.VE
.LP
The line breaks chosen by
.B par
are clearly more pleasing.
.LP
I use
.B par
in conjunction with the !} command of the
.B vi
editor. Other editors probably provide
a similar feature for filtering text.
.LP
The rest of this section is a series of
before-and-after pictures showing some typical uses of
.BR par .
.LP
Before:
.VS
          Four score and seven years ago, our fathers brought
        forth on this continent
        a new nation.
.VE
.LP
After
.CM "par 42"
.VS
          Four score and seven years ago,
        our fathers brought forth on this
        continent a new nation.
.VE
.LP
Before:
.VS
        /* Four score and seven years */
        /* ago, our */
        /* fathers brought forth on this continent */
        /* a new nation. */
.VE
.LP
After
.CM "par 42"
.VS
        /* Four score and seven years   */
        /* ago, our fathers brought     */
        /* forth on this continent a    */
        /* new nation.                  */
.VE
.LP
Or after
.CM "par l 42"
.VS
        /* Four score and seven    */
        /* years ago, our fathers  */
        /* brought forth on this   */
        /* continent a new nation. */
.VE
.LP
Or after
.CM "par l 42 m0"
.VS
        /* Four score and seven         */
        /* years ago, our fathers       */
        /* brought forth on this        */
        /* continent a new nation.      */
.VE
.LP
Before:
.VS
        Gettysburg Address: Four score
                            and seven years ago,
                            our fathers brought forth on
                            this continent
                            a new nation.
.VE
.LP
After
.CM "par h 56"
.VS
        Gettysburg Address: Four score and seven years
                            ago, our fathers brought
                            forth on this continent a
                            new nation.
.VE
.LP
Before:
.VS
        1  Four score and
        2  seven years ago,
        3  our fathers brought
        4  forth on this continent
        5  a new nation.
.VE
.LP
After
.CM "par p11 44"
.VS
        1  Four score and seven years ago,
        2  our fathers brought forth on this
        3  continent a new nation.
.VE
.SH SEE ALSO
.LP
.B par.doc
.SH LIMITATIONS
.LP
If you like two spaces between sentences, too
bad. Differentiating between periods that end
sentences and periods used in abbreviations
is a complex problem beyond the scope of this
simple filter. Consider the following tough case:
.VS
        I calc'd the approx.
        Fermi level to 3 sig. digits.
.VE
.LP
Suppose that that should be reformatted to:
.VS
        I calc'd the approx. Fermi
        level to three sig. digits.
.VE
.LP
The program has to decide whether to put 1 or 2 spaces
between \*Qapprox.\*U and \*QFermi\*U. There is no obvious
hint from the original paragraph because there was a line
break between them, and \*QFermi\*U begins with a capital
letter. The program would apparently have to understand
English grammar to determine that the sentence does not
end there (and then it would only work for English text).
.LP
If you use tabs, you probably won't like the way
.B par
handles
(or doesn't handle) them. It treats them just like spaces.
I didn't bother trying to make sense of tabs because they
don't make sense to begin with. Not everyone's terminal
has the same tab settings, so text files containing
tabs are sometimes mangled. In fact, almost every text
file containing tabs gets mangled when something is
inserted at the beginning of each line (when quoting
e-mail or commenting out a section of a shell script, for
example), making them a pain to edit. In my opinion, the
world would be a nicer place if everyone stopped using
tabs (so I'm doing my part by not supporting them in
.BR par .)
.LP
There is currently no way for the length of the
output prefix to differ from the length of the
input prefix. Ditto for the suffix. I may consider
adding this capability in a future release, but
right now I'm not sure how I'd want it to work.
.SH BUGS
.LP
If I knew of any bugs, I wouldn't have released the package.
Of course, there may be bugs that I haven't yet discovered.
.LP
If you find any bugs, or if you have
any suggestions, please send e-mail to:
.RS
.LP
amc@wuecl.wustl.edu
.RE
.LP
or send paper mail to:
.RS
.LP
.nf
Adam M. Costello
Campus Box 1045
Washington University
One Brookings Dr.
St. Louis, MO 63130
USA
.fi
.RE
.LP
Note that both addresses could
change anytime after June 1994.
.LP
When reporting a bug, please include the exact input and
command line options used, and the version number of
.BR par ,
so that I can reproduce it.