About panda

Panda is a Pandoc Lua filter that works on internal Pandoc’s AST.

It provides several interesting features:

• variable expansion (minimalistic templating)
• conditional blocks
• file inclusion (e.g. for source code examples)
• script execution (e.g. to include the result of a command)
• diagrams (Graphviz, PlantUML, ditaa, Asymptote, blockdiag, mermaid…)

Panda is heavily inspired by abp reimplemented as a Pandoc Lua filter.

If you need a more generic text preprocessor, UPP may be a better choice.

Open source

Panda is an Open source software. Anybody can contribute on GitHub to:

• suggest or add new features
• report or fix bugs
• improve the documentation
• add some nicer examples
• find new usages
• …

Installation

1. Download the sources: git clone https://github.com/CDSoft/panda.
2. Run make test to run tests.
3. Run make install to install panda and panda.lua to ~/.local/bin (see INSTALL_PATH in Makefile).

panda and panda.lua can also be installed anywhere. Nothing else is required (except from Pandoc obviously).

Usage

panda.lua is a Pandoc Lua filter and is not meant to be called directly. panda is just a shell script that calls pandoc -L panda.lua ....

$ pandoc -L panda.lua ...

or

$ panda ...

A complete example is given as a Makefile in the doc directory.

Cheat sheet

Commented blocks

Div blocks with the comment class are commented:

::: comment
This block is a comment and is discarded by panda.
:::

String expansion

panda stores variables in an environment used to expand strings. Variables can be defined by a Lua script with the meta class. The include attribute can also be used to point to an external file. Variables can only contain inline elements, not blocks.

The initial environment contains:

• the environment variables
• the document metadata (title, author, date)

Variable names are enclosed between double curly brackets.

E.g.:

```meta
foo = "bar (note: this is parsed as **Markdown**)"
```

foo is {{foo}}.

```{.meta include=foo.lua}
This text is ignored, definitions are in foo.lua.
```

foo is defined in `foo.lua` and is {{foo}}.

Conditional blocks

Blocks can be conditionally kept or omitted. The condition is described with attributes.

:::{.if name="value"}
This block is emitted only if the value of the variable "name" is "value"
:::

Div inclusion

Fragments of documents can be imported from external files. The include attribute contains the name of the file to include. The content of the file is parsed according to its format (deduced from its name) and replaces the div block content.

:::{include=file.md shift=n}
This text is optional and will be replaced by the content of file.md.
Section title levels are shifted by n (0 if not specified).
:::

The included file can be in a different format (e.g. a markdown file can include a reStructuredText file).

Block inclusion

Code examples can be imported from external files. The include attribute contains the name of the file to include. The content of the file replaces the code block content.

```{.c include=foo.c fromline=3 toline=10 pattern="Lua string pattern" format="%1"}
This text is optional and will be replaced by the content of foo.c.
```

The optional fromline and toline defines the first and last lines to be included.

The optional pattern describes the part of the text that will be rendered. The format uses the captures defined by the pattern to format the content of the block ("%1" if not defined).

Scripts

Scripts can be executed by inline or code blocks. The cmd attribute defines the command to execute. The content of the block is in a temporary file which name is added to the command. If the command contains the %s char, it is replaced by the temporary file name. If the command does not contain any %s, the file name is appended to the command. The result replaces the content of the code block.

icmd can be used instead of cmd to let Pandoc parse the result of the command and include it in the document as a Span or Div node.

```{.python cmd=python}
print("Hello from Python!")
```

Hello from Python!

Lua says `print "Hello from Lua!"`{icmd=lua}

Diagrams

Code blocks containing diagrams are replaced with an image resulting from the diagram source code.

The render command is the render field. The output image can be a hash computed from the diagram source code or the value of the img field. The optional out field overloads img to change the output directory when rendering the diagram.

The description of the image is in the caption and alt fields. caption is the caption of the diagram. alt is the alternative description of the diagram. The optional target field is a URL pointed by the image.

In the render command, %i is replaced by the name of the input document (generated from the content of the code block) and %o by the name of the output image file (generated from the img field).

The img field is optional. The default value is a name generated in the directory given by the environment variable PANDA_CACHE (.panda if PANDA_CACHE is not defined).

If img contains %h, it is replaced by a hash computed from the diagram source.

The file format (extension) must be in the render field, after the %o tag (e.g.: %o.png), not in the img field.

``` { render="{{plantuml}}"
      img="img/panda_plantuml_demo"
      out="{{build}}/img"
      caption="Caption"
      alt="Alternative description" }
@startuml
Alice -> Bob: hello
@enduml
```

Some render commands are predefined:

Notes:

• dot: GraphViz support also includes dot, neato, twopi, circo, fdp, sfdp, patchwork and osage.

• plantuml: PLANTUML can be defined as an environment variable. Its default value is the directory of the panda.lua script appended with "plantuml.jar".

• ditaa: DITAA can be defined as an environment variable. Its default value is the directory of the panda.lua script appended with "ditaa.jar".

• blockdiag: Blockdiag support also includes actdiag, blockdiag, nwdiag, packetdiag, rackdiag and seqdiag.

• renderers without an explicit image format are built differently according to the output document format.

  • For PDF (LaTeX) documents, the default format is PDF
  • For other documents, the default format is SVG
  • The file extension is added to the img field

E.g.:

```{.dot render="dot -Tsvg -o %o.svg %i"
         img="img/panda_diagram_example"
         out="./img" }
digraph {
    rankdir=LR;
    input -> pandoc -> output
    pandoc -> panda -> {pandoc, diagrams}
    { rank=same; pandoc, panda }
    { rank=same; diagrams, output }
}
```

```{ render="gnuplot -e 'set terminal svg' -e 'set output "%o.svg"' -c %i"
     img="img/panda_gnuplot_example"
     out="./img" }
set xrange [-pi:pi]
set yrange [-1.5:1.5]
plot sin(x) lw 4, cos(x) lw 4
```

Filters can be combined. E.g.: a diagram can be stored in an external file, included and rendered by panda.

The file `hello.dot` contains:

```{.dot include="./hello.dot"
         pattern="digraph%s*%b{}" }
```

digraph {
    rankdir=LR;
    Hello -> World;
}

and is rendered as:

```{ render="dot -Tsvg -o %o.svg %i"
     img="img/hello"
     out="./img"
     include="./hello.dot" }
```

The img and out fields are optional. This is especially useful in self-contained documents. The image name is generated from a hash value of the diagram.

E.g.:

```{ render="dot -Tsvg -o %o.svg %i"
     include="./hello.dot" }
```

Makefile dependencies

It is sometimes useful to build a dependency list on the fly. panda can generate a dependency list for make, in the same vein than the gcc -M option. The environment variable PANDA_TARGET must be defined with the target name. panda will generate a file named ${PANDA_TARGET}.d containing the dependencies of ${PANDA_TARGET}.

The dependency filename can be redefined with the environment variable PANDA_DEP_FILE (e.g. to save the dependency file in a different directory).

E.g.:

PANDA_TARGET=index.html panda index.md -o index.html

This will produce a file named index.html.d containing index.html: ....

Licenses

Panda

Panda is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

Panda is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with Panda.  If not, see <https://www.gnu.org/licenses/>.

For further information about Panda you can visit
http://cdelord.fr/panda

Feedback

Your feedback and contributions are welcome. You can contact me at cdelord.fr.