Text::Autoformat - Automatic and manual text wrapping and reformating formatting


NAME

Text::Autoformat - Automatic and manual text wrapping and reformating formatting


VERSION

This document describes version 1.04 of Text::Autoformat, released December 5, 2000.


SYNOPSIS

 # Minimal use: read from STDIN, format to STDOUT...
        use Text::Autoformat;
        autoformat;
 # In-memory formatting...
        $formatted = autoformat $rawtext;
 # Configuration...
        $formatted = autoformat $rawtext, { %options };
 # Margins (1..72 by default)...
        $formatted = autoformat $rawtext, { left=>8, right=>70 };
 # Justification (left by default)...
        $formatted = autoformat $rawtext, { justify => 'left' };
        $formatted = autoformat $rawtext, { justify => 'right' };
        $formatted = autoformat $rawtext, { justify => 'full' };
        $formatted = autoformat $rawtext, { justify => 'centre' };
 # Filling (does so by default)...
        $formatted = autoformat $rawtext, { fill=>0 };
 # Squeezing whitespace (does so by default)...
        $formatted = autoformat $rawtext, { squeeze=>0 };
 # Case conversions...
        $formatted = autoformat $rawtext, { case => 'lower' };
        $formatted = autoformat $rawtext, { case => 'upper' };
        $formatted = autoformat $rawtext, { case => 'sentence' };
        $formatted = autoformat $rawtext, { case => 'title' };
        $formatted = autoformat $rawtext, { case => 'highlight' };


BACKGROUND

The problem

Perl plaintext formatters just aren't smart enough. Given a typical piece of plaintext in need of formatting:

        In comp.lang.perl.misc you wrote:
        : > <CN = Clooless Noobie> writes:
        : > CN> PERL sux because:
        : > CN>    * It doesn't have a switch statement and you have to put $
        : > CN>signs in front of everything
        : > CN>    * There are too many OR operators: having |, || and 'or'
        : > CN>operators is confusing
        : > CN>    * VB rools, yeah!!!!!!!!!
        : > CN> So anyway, how can I stop reloads on a web page?
        : > CN> Email replies only, thanks - I don't read this newsgroup.
        : >
        : > Begone, sirrah! You are a pathetic, Bill-loving, microcephalic
        : > script-infant.
        : Sheesh, what's with this group - ask a question, get toasted! And how
        : *dare* you accuse me of Ianuphilia!

both the venerable Unix fmt tool and Perl's standard Text::Wrap module produce:

        In comp.lang.perl.misc you wrote:  : > <CN = Clooless Noobie>
        writes:  : > CN> PERL sux because:  : > CN>    * It doesn't
        have a switch statement and you have to put $ : > CN>signs in
        front of everything : > CN>    * There are too many OR
        operators: having |, || and 'or' : > CN>operators is confusing
        : > CN>    * VB rools, yeah!!!!!!!!!  : > CN> So anyway, how
        can I stop reloads on a web page?  : > CN> Email replies only,
        thanks - I don't read this newsgroup.  : > : > Begone, sirrah!
        You are a pathetic, Bill-loving, microcephalic : >
        script-infant.  : Sheesh, what's with this group - ask a
        question, get toasted! And how : *dare* you accuse me of
        Ianuphilia!

Other formatting modules -- such as Text::Correct and Text::Format -- provide more control over their output, but produce equally poor results when applied to arbitrary input. They simply don't understand the structural conventions of the text they're reformatting.

The solution

The Text::Autoformat module provides a subroutine named autoformat that wraps text to specified margins. However, autoformat reformats its input by analysing the text's structure, so it wraps the above example like so:

        In comp.lang.perl.misc you wrote:
        : > <CN = Clooless Noobie> writes:
        : > CN> PERL sux because:
        : > CN>    * It doesn't have a switch statement and you
        : > CN>      have to put $ signs in front of everything
        : > CN>    * There are too many OR operators: having |, ||
        : > CN>      and 'or' operators is confusing
        : > CN>    * VB rools, yeah!!!!!!!!! So anyway, how can I
        : > CN>      stop reloads on a web page? Email replies
        : > CN>      only, thanks - I don't read this newsgroup.
        : >
        : > Begone, sirrah! You are a pathetic, Bill-loving,
        : > microcephalic script-infant.
        : Sheesh, what's with this group - ask a question, get toasted!
        : And how *dare* you accuse me of Ianuphilia!

Note that the various quoting conventions have been observed. In fact, their structure has been used to determine where some paragraphs begin. Furthermore autoformat correctly distinguished between the leading '*' bullets of the nested list (which were outdented) and the leading emphatic '*' of ``*dare*'' (which was inlined).


DESCRIPTION

Paragraphs

The fundamental task of the autoformat subroutine is to identify and rearrange independent paragraphs in a text. Paragraphs typically consist of a series of lines containing at least one non-whitespace character, followed by one or more lines containing only optional whitespace. This is a more liberal definition than many other formatters use: most require an empty line to terminate a paragraph. Paragraphs may also be denoted by bulleting, numbering, or quoting (see the following sections).

Once a paragraph has been isolated, autoformat fills and re-wraps its lines according to the margins that are specified in its argument list. These are placed after the text to be formatted, in a hash reference:

        $tidied = autoformat($messy, {left=>20, right=>60});

By default, autoformat uses a left margin of 1 (first column) and a right margin of 72.

Normally, autoformat only reformats the first paragraph it encounters, and leaves the remainder of the text unaltered. This behaviour is useful because it allows a one-liner invoking the subroutine to be mapped onto a convenient keystroke in a text editor, to provide one-paragraph-at-a-time reformatting:

        % cat .exrc
        map f !Gperl -MText::Autoformat -e'autoformat'

(Note that to facilitate such one-liners, if autoformat is called in a void context without any text data, it takes its text from STDIN and writes its result to STDOUT).

To enable autoformat to rearrange the entire input text at once, the all argument is used:

        $tidied_all = autoformat($messy, {left=>20, right=>60, all=>1});

Bulleting and (re-)numbering

Often plaintext will include lists that are either:

        * bulleted,
        * simply numbered (i.e. 1., 2., 3., etc.), or
        * hierarchically numbered (1, 1.1, 1.2, 1.3, 2, 2.1. and so forth).

In such lists, each bulleted item is implicitly a separate paragraph, and is formatted individually, with the appropriate indentation:

        * bulleted,
        * simply numbered (i.e. 1., 2., 3.,
          etc.), or
        * hierarchically numbered (1, 1.1,
          1.2, 1.3, 2, 2.1. and so forth).

More importantly, if the points are numbered, the numbering is checked and reordered. For example, a list whose points have been rearranged:

        2. Analyze problem
        3. Design algorithm
        1. Code solution
        5. Test
        4. Ship

would be renumbered automatically by autoformat:

        1. Analyze problem
        2. Design algorithm
        3. Code solution
        4. Ship
        5. Test

The same reordering would be performed if the ``numbering'' was by letters (a. b. c. etc.) or Roman numerals (i. ii. iii.) or by some combination of these (1a. 1b. 2a. 2b. etc.) Handling disordered lists of letters and Roman numerals presents an interesting challenge. A list such as:

        C. Put cat in box.
        D. Close lid.
        E. Activate Geiger counter.

should be reordered as A. B. C., whereas:

        C. Put cat in box.
        D. Close lid.
        XLI. Activate Geiger counter.

should be reordered I. II. III.

The autoformat subroutine solves this problem by always interpreting alphabetic bullets as being letters, unless the full list consists only of valid Roman numerals, at least one of which is two or more characters long.

Quoting

Another case in which contiguous lines may be interpreted as belonging to different paragraphs, is where they are quoted with distinct quoters. For example:

        : > CN> So anyway, how can I stop reloads on a web page?
        : > CN> Email replies only, thanks - I don't read this newsgroup.
        : > Begone, sirrah! You are a pathetic, Bill-loving,
        : > microcephalic script-infant.
        : Sheesh, what's with this group - ask a question, get toasted!
        : And how *dare* you accuse me of Ianuphilia!

autoformat recognizes the various quoting conventions used in this example and treats it as three paragraphs to be independently reformatted.

Block quotations present a different challenge. A typical formatter would render the following quotation:

        "We are all of us in the gutter,
         but some of us are looking at the stars"
                                -- Oscar Wilde

like so:

        "We are all of us in the gutter, but some of us are looking at
        the stars" -- Oscar Wilde

autoformat recognizes the quotation structure by matching the following regular expression against the text component of each paragraph:

        / \A(\s*)               # leading whitespace for quotation
          (["']|``)             # opening quotemark
          (.*)                  # quotation
          (''|\2)               # closing quotemark
          \s*?\n                # trailing whitespace after quotation
          (\1[ ]+)              # leading whitespace for attribution
                                #   (must be indented more than quotation)
          (--|-)                # attribution introducer
          ([^\n]*?\n)           # first attribution line
          ((\5[^\n]*?$)*)       # other attribution lines 
                                #   (indented no less than first line)
          \s*\Z                 # optional whitespace to end of paragraph
        /xsm

When reformatted (see below), the indentation and the attribution structure will be preserved:

        "We are all of us in the gutter, but some of us are looking
         at the stars"
                                -- Oscar Wilde

Widow control

Note that in the last example, autoformat broke the line at column 68, four characters earlier than it should have. It did so because, if the full margin width had been used, the formatting would have left the last two words by themselves on an oddly short last line:

        "We are all of us in the gutter, but some of us are looking at
         the stars"

This phenomenon is known as ``widowing'' and is heavily frowned upon in typesetting circles. It looks ugly in plaintext too, so autoformat avoids it by stealing extra words from earlier lines in a paragraph, so as to leave enough for a reasonable last line. The heuristic used is that final lines must be at least 10 characters long (though this number may be adjusted by passing a widow => minlength argument to autoformat).

If the last line is too short, the paragraph's right margin is reduced by one column, and the paragraph is reformatted. This process iterates until either the last line exceeds nine characters or the margins have been narrowed by 10% of their original separation. In the latter case, the reformatter gives up and uses its original formatting.

Justification

The autoformat subroutine also takes a named argument: {justify =E<gt> I<type>}, which specifies how each paragraph is to be justified. The options are: 'left' (the default), 'right', 'centre' (or 'center'), and 'full'. These act on the complete paragraph text (but not on any quoters before that text). For example, with 'right' justification:

        R3>     Now is the Winter of our discontent made
        R3> glorious Summer by this son of York. And all
        R3> the clouds that lour'd upon our house In the
        R3>              deep bosom of the ocean buried.

Full justification is interesting in a fixed-width medium like plaintext because it usually results in uneven spacing between words. Typically, formatters provide this by distributing the extra spaces into the first available gaps of each line:

        R3> Now  is  the  Winter  of our discontent made
        R3> glorious Summer by this son of York. And all
        R3> the  clouds  that  lour'd  upon our house In
        R3> the deep bosom of the ocean buried.

This produces a rather jarring visual effect, so autoformat reverses the strategy and inserts extra spaces at the end of lines:

        R3> Now is the Winter  of  our  discontent  made
        R3> glorious Summer by this son of York. And all
        R3> the clouds that lour'd  upon  our  house  In
        R3> the deep bosom of the ocean buried.

Most readers find this less disconcerting.

Implicit centring

Even if explicit centring is not specified, autoformat will attempt to automatically detect centred paragraphs and preserve their justification. It does this by examining each line of the paragraph and asking: ``if this line were part of a centred paragraph, where would the centre line have been?''

The answer can be determined by adding the length of leading whitespace before the first word, plus half the length of the full set of words on the line. That is, for a single line:

        $line =~ /^(\s*)(.*?)(\s*)$/
        $centre = length($1)+0.5*length($2);

By making the same estimate for every line, and then comparing the estimates, it is possible to deduce whether all the lines are centred with respect to the same axis of symmetry (with an allowance of &plusminus;1 to cater for the inevitable rounding when the centre positions of even-length rows were originally computed). If a common axis of symmetry is detected, autoformat assumes that the lines are supposed to be centred, and switches to centre-justification mode for that paragraph.

Case transformations

The autoformat subroutine can also optionally perform case conversions on the text it processes. The {case => type} argument allows the user to specify five different conversions:

'upper'
This mode unconditionally converts every letter in the reformatted text to upper-case;

'lower'
This mode unconditionally converts every letter in the reformatted text to lower-case;

'sentence'
This mode attempts to generate correctly-cased sentences from the input text. That is, the first letter after a sentence-terminating punctuator is converted to upper-case. Then, each subsequent word in the sentence is converted to lower-case, unless that word is originally mixed-case or contains punctuation. For example, under {case => 'sentence'}:
        'POVERTY, MISERY, ETC. are the lot of the PhD candidate. alas!'

becomes:

        'Poverty, misery, etc. are the lot of the PhD candidate. Alas!'

Note that autoformat is clever enough to recognize that the period after abbreviations such as etc. is not a sentence terminator.

If the argument is specified as 'sentence ' (with one or more trailing whitespace characters) those characters are used to replace the single space that appears at the end of the sentence. For example, autoformat($text, {case=>'sentence '}) would produce:

        'Poverty, misery, etc. are the lot of the PhD candidate.  Alas!'

'title'
This mode behaves like 'sentence' except that the first letter of every word is capitalized:
        'What I Did On My Summer Vacation In Monterey'

'highlight'
This mode behaves like 'title' except that trivial words are not capitalized:
        'What I Did on my Summer Vacation in Monterey'


OTHER FEATURES

The form sub

The form() subroutine may be exported from the module. It takes a series of format (or ``picture'') strings followed by replacement values, interpolates those values into each picture string, and returns the result. The effect is similar to the inbuilt perl format mechanism, although the field specification syntax is simpler and some of the formatting behaviour is more sophisticated.

A picture string consists of sequences of the following characters:

<
Left-justified field indicator. A series of sequential <'s specify a left-justified field to be filled by a subsequent value.

>
Right-justified field indicator. A series of sequential >'s specify a right-justified field to be filled by a subsequent value.

^
Centre-justified field indicator. A series of sequential ^'s specify a centred field to be filled by a subsequent value.

>>>.<<<<
A numerically formatted field with the specified number of digits to either side of the decimal place. See Numerical formatting below.

[
Left-justified block field indicator. Just like a < field, except it repeats as required on subsequent lines. See below.

]
Right-justified block field indicator. Just like a > field, except it repeats as required on subsequent lines. See below.

|
Centre-justified block field indicator. Just like a ^ field, except it repeats as required on subsequent lines. See below.

]]].[[[[
A numerically formatted block field with the specified number of digits to either side of the decimal place. Just like a >>>.<<<< field, except it repeats as required on subsequent lines. See below.

\
Literal escape of next character (e.g. \| is formatted as '|', not a one character wide centre-justified block field).

Any other character
That literal character.

Any substitution value which is undef (either explicitly so, or because it is missing) is replaced by an empty string.

Controlling line filling.

Note that, unlike the a perl format, form preserves whitespace (including newlines) unless called with certain options.

The ``squeeze'' option (when specified with a true value) causes any sequence of spaces and/or tabs (but not newlines) in an interpolated string to be replaced with a single space.

The ``fill'' option causes newlines to also be squeezed.

Hence:

        $frmt = "# [[[[[[[[[[[[[[[[[[[[[";
        $data = "h  e\t \tl lo\nworld\t\t\t\t\t";
        print form $frmt, $data;
        # h  e            l lo
        # world
        print form {squeeze=>1}, $frmt, $data;
        # h e l lo
        # world
        print form {fill=>1}, $frmt, $data;
        # h  e            l lo world
        print form {squeeze=>1, fill=>1}, $frmt, $data;
        # h e l lo world

Whether or not filling or squeezing is in effect, form can also be directed to trim any extra whitespace from the end of each line it formats, using the ``trim'' option. If this option is specified with a true value, every line returned by form will automatically have the substitution s/[ \t]+$//gm applied to it.

Hence:

        print length form "[[[[[[[[[[", "short";
        # 11
        print length form {trim=>1}, "[[[[[[[[[[", "short";
        # 6

Temporary and permanent default options

If form is called with options, but no template string or data, it resets it's defaults to the options specified. If called in a void context:

        form { squeeze => 1, trim => 1 };

the options become permanent defaults.

However, when called with only options in non-void context, form resets its defaults to those options and returns an object. The reset default values persist only until that returned object is destroyed. Hence to temporarily reset form's defaults within a single subroutine:

        sub single {
                my $tmp = form { squeeze => 1, trim => 1 };
                # do formatting with the obove defaults
        } # form's defaults revert to previous values as $tmp object destroyed

How form hyphenates

Any line with a block field repeats on subsequent lines until all block fields on that line have consumed all their data. Non-block fields on these lines are replaced by the appropriate number of spaces.

Words are wrapped whole, unless they will not fit into the field at all, in which case they are broken and (by default) hyphenated. Simple hyphenation is used (i.e. break at the N-1th character and insert a '-'), unless a suitable alternative subroutine is specified instead.

Words will not be broken if the break would leave less than 2 characters on the current line. This minimum can be varied by setting the 'minbreak' option to a numeric value indicating the minumum total broken characters (including hyphens) required on the current line. Note that, for very narrow fields, words will still be broken (but unhyphenated). For example:

        print form '|', 'split';

would print:

        s
        p
        l
        i
        t

whilst:

        print form {minbreak=>1}, '|', 'split';

would print:

        s-
        p-
        l-
        i-
        t

Alternative breaking subroutines can be specified using the ``break'' option in a configuration hash. For example:

        form { break => \&my_line_breaker }
             $format_str,
             @data;

form expects any user-defined line-breaking subroutine to take three arguments (the string to be broken, the maximum permissible length of the initial section, and the total width of the field being filled). The hypenate sub must return a list of two strings: the initial (broken) section of the word, and the remainder of the string respectively).

For example:

        sub tilde_break = sub($$$)
        {
                (substr($_[0],0,$_[1]-1).'~', substr($_[0],$_[1]-1));
        }
        form { break => \&tilde_break }
             $format_str,
             @data;

makes '~' the hyphenation character, whilst:

        sub wrap_and_slop = sub($$$)
        {
                my ($text, $reqlen, $fldlen) = @_;
                if ($reqlen==$fldlen) { $text =~ m/\A(\s*\S*)(.*)/s }
                else                  { ("", $text) }
        }
        form { break => \&wrap_and_slop }
             $format_str,
             @data;

wraps excessively long words to the next line and ``slops'' them over the right margin if necessary.

The Text::Autoformat package provides three functions to simplify the use of variant hyphenation schemes. The exportable subroutine Text::Autoformat::break_wrap generates a reference to a subroutine implementing the ``wrap-and-slop'' algorithm shown in the last example, which could therefore be rewritten:

        use Text::Autoformat qw( form break_wrap );
        form { break => break_wrap }
             $format_str,
             @data;

The subroutine Text::Autoformat::break_with takes a single string argument and returns a reference to a sub which hyphenates with that string. Hence the first of the two examples could be rewritten:

        use Text::Autoformat qw( form break_wrap );
        form { break => break_with('~') }
             $format_str,
             @data;

The subroutine Text::Autoformat::break_TeX returns a reference to a sub which hyphenates using Jan Pazdziora's TeX::Hyphen module. For example:

        use Text::Autoformat qw( form break_wrap );
        form { break => break_TeX }
             $format_str,
             @data;

Note that in the previous examples there is no leading '\&' before break_wrap, break_with, or break_TeX, since each is being directly called (and returns a reference to some other suitable subroutine);

The form formatting algorithm

The algorithm form uses is:

        1. split the first string in the argument list
           into individual format lines and add a terminating
           newline (unless one is already present).
        2. for each format line...
                2.1. determine the number of fields and shift
                     that many values off the argument list and
                     into the filling list. If insufficient
                     arguments are available, generate as many 
                     empty strings as are required.
                2.2. generate a text line by filling each field
                     in the format line with the initial contents
                     of the corresponding arg in the filling list
                     (and remove those initial contents from the arg).
                2.3. replace any <,>, or ^ fields by an equivalent
                     number of spaces. Splice out the corresponding
                     args from the filling list.
                2.4. Repeat from step 2.2 until all args in the
                     filling list are empty.
        3. concatenate the text lines generated in step 2
        4. repeat from step 1 until the argument list is empty

form examples

As an example of the use of form, the following:

        $count = 1;
        $text = "A big long piece of text to be formatted exquisitely";
        print form q
        {
                ||||  <<<<<<<<<<
                ----------------
                ^^^^  ]]]]]]]]]]\|
                                =
                ]]].[[[

        }, $count, $text, $count+11, $text, "123 123.4\n123.456789";

produces the following output:

                 1    A big long
                ----------------
                 12     piece of|
                      text to be|
                       formatted|
                      exquisite-|
                              ly|
                                =
                123.0
                123.4
                123.456

Picture strings and replacement values can be interleaved in the traditional format format, but care is needed to ensure that the correct number of substitution values are provided. For example:

        $report = form
                'Name           Rank    Serial Number',
                '====           ====    =============',
                '<<<<<<<<<<<<<  ^^^^    <<<<<<<<<<<<<',
                 $name,         $rank,  $serial_number,
                ''
                'Age    Sex     Description',
                '===    ===     ===========',
                '^^^    ^^^     [[[[[[[[[[[',
                 $age,  $sex,   $description;

How form consumes strings

Unlike format, within form non-block fields do consume the text they format, so the following:

        $text = "a line of text to be formatted over three lines";
        print form "<<<<<<<<<<\n  <<<<<<<<\n    <<<<<<\n",
                    $text,        $text,        $text;

produces:

        a line of
          text to
            be fo-

not:

        a line of
          a line 
            a line

To achieve the latter effect, convert the variable arguments to independent literals (by double-quoted interpolation):

        $text = "a line of text to be formatted over three lines";
        print form "<<<<<<<<<<\n  <<<<<<<<\n    <<<<<<\n",
                   "$text",      "$text",      "$text";

Although values passed from variable arguments are progressively consumed within form, the values of the original variables passed to form are not altered. Hence:

        $text = "a line of text to be formatted over three lines";
        print form "<<<<<<<<<<\n  <<<<<<<<\n    <<<<<<\n",
                    $text,        $text,        $text;
        print $text, "\n";

will print:

        a line of
          text to
            be fo-
        a line of text to be formatted over three lines

To cause form to consume the values of the original variables passed to it, pass them as references. Thus:

        $text = "a line of text to be formatted over three lines";
        print form "<<<<<<<<<<\n  <<<<<<<<\n    <<<<<<\n",
                    \$text,       \$text,       \$text;
        print $text, "\n";

will print:

        a line of
          text to
            be fo-
        rmatted over three lines

Note that, for safety, the ``non-consuming'' behaviour takes precedence, so if a variable is passed to form both by reference and by value, its final value will be unchanged.

Numerical formatting

The ``>>>.<<<'' and ``]]].[[['' field specifiers may be used to format numeric values about a fixed decimal place marker. For example:

        print form '(]]]]].[[)', <<EONUMS;
                   1
                   1.0
                   1.001
                   1.009
                   123.456
                   1234567
                   one two
        EONUMS

would print:


        (    1.0 )
        (    1.0 )
        (    1.00)
        (    1.01)
        (  123.46)
        (#####.##)
        (?????.??)
        (?????.??)

Fractions are rounded to the specified number of places after the decimal, but only significant digits are shown. That's why, in the above example, 1 and 1.0 are formatted as ``1.0'', whilst 1.001 is formatted as ``1.00''.

You can specify that the maximal number of decimal places always be used by giving the configuration option 'numeric' a value that matches /\bAllPlaces\b/i. For example:

        print form { numeric => AllPlaces },
                   '(]]]]].[[)', <<'EONUMS';
                   1
                   1.0
        EONUMS

would print:


        (    1.00)
        (    1.00)

Note that although decimal digits are rounded to fit the specified width, the integral part of a number is never modified. If there are not enough places before the decimal place to represent the number, the entire number is replaced with hashes.

If a non-numeric sequence is passed as data for a numeric field, it is formatted as a series of question marks. This querulous behaviour can be changed by giving the configuration option 'numeric' a value that matches /\bSkipNaN\b/i in which case, any invalid numeric data is simply ignored. For example:

        print form { numeric => 'SkipNaN' }
                   '(]]]]].[[)',
                   <<EONUMS;
                   1
                   two three
                   4
        EONUMS

would print:


        (    1.0 )
        (    4.0 )

Filling block fields with lists of values

If an argument corresponding to a field is an array reference, then form automatically joins the elements of the array into a single string, separating each element with a newline character. As a result, a call like this:

        @values = qw( 1 10 100 1000 );
        print form "(]]]].[[)", \@values;

will print out

         (   1.00)
         (  10.00)
         ( 100.00)
         (1000.00)

as might be expected.

Note however that arrays must be passed by reference (so that form knows that the entire array holds data for a single field). If the previous example had not passed @values by reference:

        @values = qw( 1 10 100 1000 );
        print form "(]]]].[[)", @values;

the output would have been:

         (   1.00)
         10
         100
         1000

This is because @values would have been interpolated into form's argument list, so only $value[0] would have been used as the data for the initial format string. The remaining elements of @value would have been treated as separate format strings, and printed out ``verbatim''.

Note too that, because arrays must be passed using a reference, their original contents are consumed by form, just like the contents of scalars passed by reference.

To avoid having an array consumed by form, pass it as an anonymous array:

        print form "(]]]].[[)", [@values];

Headers, footers, and pages

The form subroutine can also insert headers, footers, and page-feeds as it formats. These features are controlled by the ``header'', ``footer'', ``pagefeed'', ``pagelen'', and ``pagenum'' options.

The ``pagenum'' option takes a scalar value or a reference to a scalar variable and starts page numbering at that value. If a reference to a scalar variable is specified, the value of that variable is updated as the formatting proceeds, so that the final page number is available in it after formatting. This can be useful for multi-part reports.

The ``pagelen'' option specifies the total number of lines in a page (including headers, footers, and page-feeds).

If the ``header'' option is specified with a string value, that string is used as the header of every page generated. If it is specified as a reference to a subroutine, that subroutine is called at the start of every page and its return value used as the header string. When called, the subroutine is passed the current page number.

Likewise, if the ``footer'' option is specified with a string value, that string is used as the footer of every page generated. If it is specified as a reference to a subroutine, that subroutine is called at the start of every page and its return value used as the footer string. When called, the footer subroutine is passed the current page number. If the option is specified as a hash, it acts as described above for the ``header'' option.

Both the header and footer options can also be specified as hash references. In this case the hash entires for keys ``left'', ``centre'' (or ``center''), and ``right'' specify what is to appear on the left, centre, and right of the header/footer. The entry for the key ``width'' specifies how wide the footer is to be. The ``left'', ``centre'', and ``right'' values may be literal strings, or subroutines (just as a normal header/footer specification may be.) See the second example, below.

The ``pagefeed'' option acts in exactly the same way, to produce a pagefeed which is appended after the footer. But note that the pagefeed is not counted as part of the page length.

All three of these page components are recomputed at the start of each new page, before the page contents are formatted (recomputing the header and footer makes it possible to determine how many lines of data to format so as to adhere to the specified page length).

When the call to form is complete and the data has been fully formatted, the footer subroutine is called one last time, with an extra argument of 1. The string returned by this final call is used as the final footer.

So for example, a 60-line per page report, starting at page 7, with appropriate headers and footers might be set up like so:

        $page = 7;
        form { header => sub { "Page $_[0]\n\n" },
               footer => sub { return "" if $_[1];
                               "-"x50 . "\n" . form ">"x50", "...".($_[0]+1);
                             },
               pagefeed => "\n\n",
               pagelen  => 60
               pagenum  => \$page,
             },
             $template,
             @data;

Note the recursive use of form within the ``footer'' option.

Alternatively, to set up headers and footers such that the running head is right justified in the header and the page number is centred in the footer:

        form { header => { right => "Running head" },
               footer => { centre => sub { "Page $_[0]" } },
               pagelen  => 60
             },
             $template,
             @data;

The tag sub

The tag subroutine may be exported from the module. It takes two arguments: a tag specifier and a text to be entagged. The tag specifier indicates the indenting of the tag, and of the text. The sub generates an end-tag (using the usual ``/tag'' variant), unless an explicit end-tag is provided as the third argument.

The tag specifier consists of the following components (in order):

An optional vertical spacer (zero or more whitespace-separated newlines)
One or more whitespace characters up to a final mandatory newline. This vertical space is inserted before the tag and after the end-tag

An optional tag indent
Zero or more whitespace characters. Both the tag and the end-tag are indented by this whitespace.

An optional left (opening) tag delimiter
Zero or more non-``word'' characters (not alphanumeric or '_'). If the opening delimiter is omitted, the character '<' is used.

A tag
One or more ``word'' characters (alphanumeric or '_').

Optional tag arguments
Any number of any characters

An optional right (closing) tag delimiter
Zero or more non-``word'' characters which balance some sequential portion of the opening tag delimiter. For example, if the opening delimiter is ``<-('' then any of the following are acceptible closing delimiters: ``)->'', ``->'', or ``>''. If the closing delimiter is omitted, the ``inverse'' of the opening delimiter is used (for example, ``)->''),

An optional vertical spacer (zero or more newlines)
One or more whitespace characters up to a mandatory newline. This vertical space is inserted before and after the complete text.

An optional text indent
Zero or more space of tab characters. Each line of text is indented by this whitespace (in addition to the tag indent).

For example:

        $text = "three lines\nof tagged\ntext";
        print tag "A HREF=#nextsection", $text;

prints:

        <A HREF=#nextsection>three lines
        of tagged
        text</A>

whereas:

        print tag "[-:GRIN>>>\n", $text;

prints:

        [-:GRIN>>>:-]
        three lines
        of tagged
        text
        [-:/GRIN>>>:-]

and:

        print tag "\n\n   <BOLD>\n\n   ", $text, "<END BOLD>";

prints:

 

           <BOLD>
              three lines
              of tagged
              text
           <END BOLD>

 

(with the indicated spacing fore and aft).


AUTHOR

Damian Conway (damian@conway.org)


BUGS

There are undoubtedly serious bugs lurking somewhere in code this funky :-) Bug reports and other feedback are most welcome.


COPYRIGHT

Copyright (c) 1997-2000, Damian Conway. All Rights Reserved. This module is free software. It may be used, redistributed and/or modified under the terms of the Perl Artistic License (see http://www.perl.com/perl/misc/Artistic.html)

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