Pod 6 Tables

The Good, the Bad, and the Ugly

The official specification for Perl 6 POD tables is located in the Documentation specification here: Tables. Although Pod 6 specifications are not completely handled properly yet, several projects are ongoing to correct the situation; one such project is ensuring the proper handling of Pod 6 tables.

As part of that effort, this document explains the current state of Pod 6 tables by example: valid tables, invalid tables, and ugly tables (i.e., valid tables that, because of sloppy construction, may result in something different than the user expects).

Restrictions

1. The only valid column separators are either visible (' | ' or ' + ') (note at least one space is required before and after the visible column separators) or invisible [two or more contiguous whitespace (WS) characters (e.g., ' ')]. Column separators are not normally recognized as such at the left or right side of a table, but one on the right side may result in one or more empty cells depending upon the number of the cells in other rows.

2. Mixing visible and invisible column separators in the same table is illegal.

3. The only valid row separator characters are '_', '-', '+', ' ', '|', and '='.

4. Consecutive interior row-separator lines are illegal.

5. Leading and trailing row-separator lines generate a warning.

HINT: During development, use of the environment variable RAKUDO_POD6_TABLE_DEBUG will show you how Rakudo interprets your pod tables before they are passed to renderers such as Pod::To::HTML, Pod::To::Text, and Pod::To::Markdown.

Best Practices

1. Use of WS for column separators is fragile, and they should only be used for simple tables. The Ugly Tables section below illustrates the problem.

2. Align table columns and rows carefully. See the examples in later best practices.

3. Don't use visual borders on the table.

4. For tables with a heading and single- or multi-line content, use one or more contiguous equal signs ('=') as the row separator after the heading, and use one or more contiguous hyphens ('-') as the row separator in the content portion of the table. For example,

=begin table
 hdr col 0 | hdr col 1
 ======================
 row 0     | row 0
 col 0     | col 1
 ----------------------
 row 1     | row 1
 col 0     | col 1
 ----------------------
=end table
=begin table
 hdr col 0   | hdr col 1
 ======================
 row 0 col 0 | row 0 col 1
 row 1 col 0 | row 1 col 1
=end table

4. For tables with no header and multi-line content, use one or more contiguous hyphens ('-') as the row separator in the content portion of the table. For example,

=begin table
 row 0       | row 0
 col 0       | col 1
 ----------------------
 row 1 col 0 | row 1 col 1
=end table

5. For tables with many rows and no multi-line content, using no row separators is fine. However, with one or more rows with multi-line content, it is easier to ensure proper results by using a row separator line (visible or invisible) between every content row.

6. Ensure intentionally empty cells have column separators, otherwise expect a warning about short rows being filled with empty cells. (Tables rows will always have the same number of cells as the row with the most cells. Short rows are padded on the right with empty cells and generate a warning.)

Note that not following best practices may require more table processing due to additional looping over table rows.

Good Tables

Following are examples of valid (Good) tables (taken from the current Specification Tests).

=begin table
        The Shoveller   Eddie Stevens     King Arthur's singing shovel
        Blue Raja       Geoffrey Smith    Master of cutlery
        Mr Furious      Roy Orson         Ticking time bomb of fury
        The Bowler      Carol Pinnsler    Haunted bowling ball
=end table
=table
    Constants           1
    Variables           10
    Subroutines         33
    Everything else     57
 
=for table
    mouse    | mice
    horse    | horses
    elephant | elephants
 
=table
    Animal | Legs |    Eats
    =======================
    Zebra  +   4  + Cookies
    Human  +   2  +   Pizza
    Shark  +   0  +    Fish
 
=table
        Superhero     | Secret          |
                      | Identity        | Superpower
        ==============|=================|================================
        The Shoveller | Eddie Stevens   | King Arthur's singing shovel
 
=begin table
 
                        Secret
        Superhero       Identity          Superpower
        =============   ===============   ===================
        The Shoveller   Eddie Stevens     King Arthur's
                                          singing shovel
 
        Blue Raja       Geoffrey Smith    Master of cutlery
 
        Mr Furious      Roy Orson         Ticking time bomb
                                          of fury
 
        The Bowler      Carol Pinnsler    Haunted bowling ball
 
=end table
=table
    X | O |
   ---+---+---
      | X | O
   ---+---+---
      |   | X
 
=table
    X   O
   ===========
        X   O
   ===========
            X
 
=begin table
 
foo
bar
 
=end table

Bad Tables

Following are examples of invalid (Bad) tables, and they should trigger an unhandled exception during parsing. They are taken from tests used in the table-pod-fix project mentioned above. After acceptance of the project's code into the Rakudo source, they will be added to the current Specification Tests. Note they may not trigger an exception at the moment, but they will after the project's code is integrated.

=begin table
r0c0 +  r0c1 | r0c3
=end table
=begin table
r0c0 +  r0c1 | r0c3
r1c0    r0c1   r0c3
=end table
=begin table
r0c0 |  r0c1
============
============
r1c0 |  r1c1
=end table

Ugly Tables

Following are examples of valid tables that are probably intended to be two columns, but the columns are not aligned well so each will parse as a single-column table.

Notice the second row has the two words separated by only one WS character, while it takes at least two adjacent WS characters to define a column separation. This is a valid table but will be parsed as a single-column table.

=begin table
r0c0    r0c1
 r1c0 r0c1
=end table

Notice the second row has the two words separated by a visible character ('|') but the character is not recognized as a column separator because it doesn't have an adjacent WS character on both sides of it. Although this is a legal table, the result will not be what the user intended because the first row has two columns while the second row has only one column, and it will thus have an empty second column.

=begin table
r0c0  |  r0c1
 r1c0 |r0c1
=end table